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New World Wine Maker Blog - Technical Articles

An Introduction to Red Wine Blending

By: Denise M. Gardner

Wine blending is often highlighted as the artistic portion of wine production.  However, blending can also be used for practical or economical purposes.  This blog post will explore some of the common introductory reasons for using wine blending to craft red wines.

Why do winemakers blend wines?

Wine blending is a wine production technique that can be used for a multitude of purposes in order to finish a wine.  Some of these reasons include, but are not limited to:

  • Creating a house style
  • Improving vintage consistency
  • Highlighting vineyard terroir
  • Enhancing a wine’s positive sensory characteristics
  • Minimizing a wine’s undesirable sensory components
  • Balancing oak flavors
  • Altering a wine’s chemistry
  • Managing wine inventory
  • Blending out (i.e., getting rid) of problem wines
  • Additional reasons…

House style and vintage consistency can be very important for a brand’s marketability and reliability amongst consumers.

Many Champagne producers rely on blending to create a house style cuvee associated with their sparkling wines.  While these are not red wines, creating a house style is often based on specific sensory or taste characteristics that are desirable by the winemaker and contribute to major blending decisions.  These blending decisions help minimize vintage-to-vintage variation and variation in grower supplies of fruit while enhancing consistency for their brand.

The same concept can be applied to red wines, but with the use of red wine grape varieties.  House blends can be represented with blending names such as “Proprietor’s Red” or “Winery’s Name House Blend.”  Having wines that are labeled as a blend provides flexibility for the winemaker to create a wine that is of a similar style on a year-to-year basis while altering the wine grape varieties that go into the blend every year.

The other advantage of creating house blends is that these wines allow winemakers to work with variations in varietal inventory.  If we take the last example above, Cupcake Vineyard’s Red Velvet wine, while three different varieties make up the blend, the percentages of each variety contributing to the blend can vary from year-to-year.  This may help mediate changes in yield each harvest season.

Improving Annual Wine Consistency or Highlighting Vintage Variation

Blending can a winemaker’s best tool in enhancing vintage consistency, especially in cooler growing regions where vintage-to-vintage variation is prevalent.  There are a couple of ways that winemakers have been able to accomplish this practice.

  1. Reserving previous vintage wines for blending into future vintages.
  2. Purchasing bulk grapes/juice/wine from warmer climatic regions and blending in small amounts to each vintage.

While neither of these practices may be ideal for terroir expression of certain wine blends, these blending practices provide opportunities to expand a winery’s product portfolio and enhance wine style variation associated with the brand.

In contrast, blending can be used as a tool to illustrate and celebrate vintage variation, which is an inherent component of winemaking.  Not only do these wines offer unique educational and marketing opportunities, this is a tactic that can be used to differentiate premium products within a brand and cater to those consumers that are wine enthusiasts or have a greater interest in vintage-to-vintage variations for a particular brand.  This practice can also better capture the brand’s terroir, which can be a key marketing feature for wineries with estate vineyards.  Additionally, these wines offer exceptional tasting experiences for consumers that enjoy vertical tastings of multiple vintage years, and can be used for various sale promotions over several years.

A common example of this practice is demonstrated by Allegro Winery & Vineyards in Brogue, PA.  The Cadenza and Bridge wines are designed as premium brands, vintage dated, and blended to a particular style in those years that produce the best quality red wine blends.

Wine blending to fix problem wines

While less artistic and perhaps a bit less creative, blending can also be used to help minimize the impact of problem wines or wines that have noticeable defects, flaws or quality shortcomings.  Minor problems can often be partially masked by being blended into aromatically rich varieties like Concord, Niagara, or Catawba.   Noiret, a red hybrid variety, also has a relatively rich aroma/flavor of black pepper which may be an alternative aromatically rich blending variety, as well as the utilization of formula wines with strong added flavors.

Wines suffering from minor oxidation problems can often be added to richer, fresher, younger wines at minimal levels without hindering the fresher or younger red wine.  Additionally, wines with a slightly elevated VA (~0.50 – 0.70 g/L acetic acid) can be added to wines with a lower VA (<0.40 g/L) after the high VA wines have been properly treated and stabilized to avoid contaminating a clean wine.

Allegro Winery’s winemaker, Carl Helrich, worked with Penn State Extension Enologist, Denise Gardner, to improve some of the Penn State-produced problem wines with use of wine blending.

Allegro Winery’s winemaker, Carl Helrich, worked with Penn State Extension Enologist, Denise Gardner, to improve some of the Penn State-produced problem wines with use of wine blending.

The key thing to remember when blending clean-wines with problem-wines is that winemakers want to avoid creating a series of lower quality wines in order to get rid of a problem wine.  Keep in mind that it is not likely that one will be able to create a “unique blend” by using problem wines to any degree.  Winemakers are more likely to create a “good enough” or “commercially acceptable” wine when utilizing blending for this purpose.

All wines that have issues should be analytically and sensorially evaluated before and after blending to ensure chemical and microbiological stability.

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When microbiology is a data problem: Putting science together to make better pictures of yeast

By Erika Szymanski of The Winoscope

Short: A Portuguese-based group is suggesting that winemakers could have more useful information about choosing a yeast strain if scientists did a better job of putting together data from different kinds of experiments.

Longer:

Scientific research generates a lot of different shapes and sizes of data. How does anyone make it work together?

Contemporary scientific research has a lot of big challenges, but here are three: funding, replicability, and integration. Funding is a great big gory topic for another day.

Replicability has seen a lot of attention in recent science news: scientists across disciplines have been reporting difficulty duplicating their colleagues’ results when they try to repeat the same experiments. This is worrisome. (Most) science is supposed to be about making observations about the world that remain the same independent of who is making the observations. Two careful people should be able to do the same experiment in two different places and obtain the same results. Well-trained scientists, however, are finding themselves unable to replicate the results described in scientific papers, and the community isn’t sure what to do about it.

Integration – how to fit together large amounts of lots of different kinds of data – looks like a separate kind of problem. Scientists (microbiologists, biochemists, systems biologists, geneticists, physicists…) study a thing – yeast, say – in many, many different ways. They generate data in many different shapes and sizes, using all manner of different kinds of instruments to make numbers that don’t just tidily line up with each other. But, at least in theory, all of those data are about the same thing – the same yeast – and so finding ways to integrate data from different kinds of experiments should massively improve our understanding of how yeast works as a whole.

The problem is a bit like trying to compile lots of different kinds of images of a large building – photos from outside and from inside, satellite images, historic accounts of parties hosted there, watercolors of the grounds, plumber’s bills, paint chips from the last remodel – into a single detailed, coherent model of the structure. You might be happy deciding to rent a house on the basis of a floor plan and a picture of the outside sometimes, but occasionally you’re going to move in and realize that the living room is wallpapered pink or that every room smells like cigar smoke and that you have a disaster on your hands that could have been averted by having more information.

Portuguese-based group of molecular biologists and biotechnologists has suggested that winemakers might have fewer fermentation disasters if scientists did a better job of integrating the different kinds of pictures they take of wine yeast. This, they note, is a “data resource” problem. Solutions lie not necessarily in doing better or different scientific research,* but in using computational or informatic tools to find points of alignment across existing kinds of data. The method they offer is unique because they can find correlations across not just two kinds of data, but three or more, and lots of it. One of the interesting things about their example for demonstrating that method is that it aligns data about yeast behavioral characteristics – qualities like low hydrogen sulfide production** – with data about genetic variability. This kind of information might help wine yeast developers increase genetic variability in yeast strains by making it easier to assess large number of potential yeast strains for the right combination of good winemaking characteristics and genetic diversity. And, consequently, their analyses could help winemakers have more complete ideas about what to expect from the yeast they choose to use.

What’s most interesting about this paper, though, is the way it points out that integration and replicability aren’t entirely separate issues. Yes, scientists doing precisely the same thing should arrive at precisely the same results. But how often do scientists do precisely the same thing? Even in trying to repeat “the same experiment,” unaccounted-for differences might interfere and yield different results. And maybe those kinds of differences are more troublesome when other living things – like yeast cells – are also participating in the experiment, compelled or willing to cooperate with the scientist to some extent but still also doing their own thing. So, a different but related question is: can the results of multiple sets of experiments make sense together? Having better computational methods for lining up different kinds of data makes it easier to find out.

*Though experiments could surely be designed so that results are easier to put together with the results of other experiments, which is very much a scientific problem.

**Important if you want to avoid making wine that smells like rotten eggs.

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2017 Pre-Bloom Disease Management Review and Discussion

Another season of grape growing is upon us and it’s a good time to review important disease management principles and be aware of some of the tools to consider integrating into your vineyard management programs this spring.

First is your annual reminder to check out the NEWA website (Network for Environment and Weather Applications) found at http://newa.cornell.edu. On the home page is a map of the Northeastern U.S. marked with the locations of hundreds of weather stations where historical and ‘up to the hour’ weather data can be viewed. Although is provided free on the internet, it is funded through the New York State IPM program. Click on a weather station near enough to you (denoted by a leaf/rain drop icon) to get weather, insect pest, and disease information you need to make important management decisions that could save you time and money. Clicking on ‘grapes’ under ‘crop pages’ will give you access to forecasting models for all the major diseases, as well as the grape berry moth degree day model that will improve your timing of grape berry moth insecticide sprays later this summer. Each model forecast is accompanied by helpful disease management messages and explanations.

Next, let’s move our minds into the upcoming pre-bloom disease management season. It’s important to recognize that the threat of disease this spring (pre-bloom) is largely determined by the amount of overwintering inoculum in your blocks. The amount of overwintering inoculum is dependent on the amount of disease that developed in your vineyard last year or in previous years. In other words, if you have kept diseases well under control in the past, especially last year, then there will be relatively little for pathogen populations to build on and cause damage, at least initially, this year. Some very practical research by Wayne Wilcox at Cornell nicely illustrates this point with powdery mildew (pm) development in susceptible wine varieties. In blocks where pm was well controlled all season, fewer overwintering structures of the fungal pathogen (chasmothecia) were available the following spring to jump start disease cycles. Early disease pressure was relatively low and early sprays were less critical to good commercial control than in blocks where disease control was poor the previous year. Where there was poor control the previous year, more of the pathogen overwintered to start disease cycles the following spring and early sprays were critical to maintaining successful commercial control. This is not to say that a bad year of pm will automatically be followed by another bad year. But it certainly tilts the odds in favor of the pathogen, especially if for some reason, you can’t manage the timely application of your early disease control program (stuff happens). It also doesn’t mean you can slack off this year if you had good control last year. Remember, there’s the weather. The weather ALWAYS plays an important role too. A good illustration of this is an experience by an organic grape grower who, in an extremely wet season, developed a serious, economically damaging case of black rot. In conventionally managed vineyards there are several very effective chemistries to control black rot, but in organic production there are no real effective fungicides, and control of this disease in organic vineyards must rely heavily on cultural measures that reduce the pathogen’s overwintering population. Of course, the grower did everything he could to sanitize the trellis of overwintering fruit mummies and bury mummies that had fallen to the ground to reduce overwintering inoculum. But fortunately, the following year was bone dry during the fruit susceptibility period and black rot was not even an issue. Had the previous wet season been followed by another wet one, I’m quite certain, the battle for control of black rot in that organic vineyard would have required ‘the kitchen sink’ to avoid losses. Unfortunately, we have no control over the weather and accurate forecasts, especially long term, are not something to rely on. But, we can (and should) strive to control overwintering inoculum levels every year and the best way to do that is good, practical, season-long disease control.

So, begin to wrap your minds around the campaign ahead. If you had poor disease control in some blocks last season, have you reviewed your spray records where control failed AND where it worked well? Where it failed, did you use the wrong material at a critical time?  I’ve had growers discuss their control failures with me only to discover that their timing was fine, but their choice of material did not cover the disease(s) they intended to control. The number of spray materials, what disease each one controls, and how well each one controls each disease, can be bewildering at times…and the list keeps growing and changing. Also, materials that used to be good choices may have become ineffective due to the development of resistance by the pathogens. For example, materials like the strobilurins (Abound, Sovran, Flint, Pristine) are no longer effective at controlling powdery and downy mildew in many parts of the east. In vineyards where this has occurred, using them during the critical fruit protection period (which used to be a great idea!) can now prove disastrous. The sterol inhibitor fungicides (Rally, Elite, Orius, Mettle, Tebusol, Tebustar, Procure, Viticure, etc) are also exhibiting the effects of resistance by the powdery mildew fungus. Though in most cases they still work on powdery to some extent, they are not appropriate for the critical fruit protection period anymore, around and shortly after bloom (products that include the more active difenoconazole are an exception on less susceptible varieties). However, they may be acceptable for maintaining a clean vineyard outside the critical period. Do you have an accurate grasp on that?

Do you have a firm grasp on the critical fruit protection period? The critical period for fruit protection from all diseases generally extends from ‘just before bloom’ to about 4 weeks later. This is the period when you need to be especially vigilant about minimizing spray intervals, using your best materials that cover all the major diseases (Phomopsis, black rot, powdery and downy mildew), focus on good coverage, etc. It is never profitable to try to cut corners during the critical period. However, if you had heavy amounts of black rot in your vineyard the year before, you should assume you have an unhealthy dose of overwintering inoculum in your vineyard this spring, and prevention of leaf lesions in the fruit zone (which would need to be addressed during the first 3-12” of shoot growth, well before the fruit protection period) would also prove to be critical. This goes for other diseases as well (refer back to the previous example with Wayne Wilcox’ powdery mildew experiment). The pre-bloom presence of visible disease in the fruit zone is a big red flag; it means you’ve got potential for serious fruit loss ahead, especially if weather conditions favor the pathogen (wet, warm, humid, calm, cloudy) during the fruit protection period that follows.

Did you record the relative levels of disease that developed in years past for each of your blocks? In order to do this, you need to be able to identify the various diseases and then scout regularly for them. This takes up valuable time but you can streamline your scouting efforts in many ways. Do you know when you would expect to first see each disease? Downy mildew doesn’t become active until about the 5-6 leaf stage. So, you know you can’t expect to see it until about that time or shortly after that. In which blocks are diseases most likely to occur first? Your block or rows next to the woods would be a good place to start, or perhaps your most susceptible variety. Blocks with the most disease last year would be a good place to start. On which parts of the vine do you expect to see diseases appear first? Can recent weather data help you to determine where to look for the disease? For example, if a black rot infection period occurred 2 weeks ago (and you can find this out easily by searching the NEWA website), would you examine the newest growth, the oldest growth, or would you look for lesions on leaves that were currently expanding and most susceptible 2 weeks ago? The answers to these questions can help you streamline your scouting efforts, save time, and improve your expertise.

Do you fully comprehend the susceptibilities of all the varieties you’re growing? You cannot spray premium Vitis vinifera like the hybrids or natives and expect the same results. What are you going to change this year to address disease control breaches in your vinifera? If you had good control last year, are you ready to do it again this year? OR, do you feel lucky and plan to back off until close to bloom to apply your first spray? I always plan for the worst when it comes to the weather and assume it’s going to be wet, cloudy, and warm; ideal for fungal disease epidemics. Consider that here in the east we are growing a highly vulnerable, susceptible host (wine grapes) on the pathogen’s ‘turf’ (the wet, humid eastern U.S.). The good news is that disease control during the pre-bloom period is generally easier (good spray coverage not a problem, low initial disease/inoculum levels, etc.) and cheaper (can use lower fungicide rates, lower spray gallonage, less expensive materials, less time, etc) than in the post bloom period, and a well prepared pre-bloom disease management program will provide extra insurance against problems during bloom and early fruit set, when your fruit ($) is most vulnerable. Now let’s review the common diseases with some of these questions and concepts in mind.

Phomopsis cane and leaf spot is often the first disease problem we face in the pre-bloom period, particularly where trellis systems maintain lots of old and/or dead wood. That’s because old and/or dead wood is where the pathogen overwinters. Therefore, the more old wood you have in your trellis, the more inoculum you can expect to be battling with this spring. Conversely, cane pruned systems have fewer problems with Phomopsis, and cane pruning/minimizing older wood is an important cultural control for this disease. Fortunately, many areas of PA and other parts of the east experienced a relatively dry spring in 2016, helping to minimize new overwintering infections on year-old wood. But, older cordons and especially dead wood and pruning stubs, can carry overwintering inoculum into many subsequent springs. So, if there was little opportunity for new Phomopsis infections to occur last year, you can still be carrying a fair amount of overwintering inoculum in old cordons and pruning stubs.

During early spring rains, Phomopsis spores flush from lesions on wood and are splashed about to invade any new shoot, leaf, and inflorescence they land on…provided the wetting period/temperature combination falls within a minimum range for infection. The basal-most (oldest) internodes of new shoots are the most susceptible to shoot infections simply because they are closest to the inoculum source; wood. In every trial where I have rated shoot infection of Phomopsis, the most severe lesion development was ALWAYS found (on average) on the first (oldest) internode region of the shoot. Lesion development typically got less severe as my rating progressed through internodes 2, 3, 4, and 5. However, once these internodes become fully expanded after the first few weeks in the season, they are no longer susceptible to lesion development. I rarely see Phomopsis lesion development beyond the fifth internode region. That’s why this disease is best dealt with preventatively, very early, during the first few inches of shoot growth. Infections that occur on the first few internodes of new shoots are not only the most likely to occur, but also the most critical; infections of inflorescences (generally on nodes 2-5) can lead to crop loss early (parts of the inflorescence may be ‘bitten off’ by the pathogen) or later during ripening (cluster stem infections in spring move into berries and cause fruit rot and shelling after veraison). And, infections that occur on the basal-most internodes, can’t all be eliminated by judicious hand pruning during the dormant season. So, in blocks where you suspect any risk of early Phomopsis infections, applications of a fungicide (mancozeb or captan are good choices) at no later than 3-6” of shoot growth are a good investment, particularly if you are not cane pruning. Following up with fungicides at 8-12” shoots and immediate pre-bloom are also important pre-bloom applications. Below are some pics from last year’s blog (Figures 1, 2) to help you get a handle on the appearance of lesions on year-old canes. Unfortunately, determining the presence of Phomopsis on older wood generally involves more than just a visual assessment.

Figure 1. Dark brown lesions on the first few internodes on these Chancellor canes are from Phomopsis infections that occurred during early shoot growth in the previous year (when these were green shoots). The buds present are just ready to burst open with new shoot growth that will be very vulnerable to infection during subsequent rain periods.

Figure 2. Although the 1” shoot stage can be vulnerable to damage from this pathogen, the more critical stage is at 3-6” shoots, when more shoot, leaf, and cluster tissue is exposed and is highly susceptible (below). Note the inflorescence in the upper right picture from which Phomopsis has “bitten off” whole branches, dramatically limiting yield potential for that cluster.

Pre-bloom fungicide applications for Powdery mildew are also prudent during early shoot growth for Vitis vinifera cultivars and highly susceptible hybrids, especially in vineyards where control of this disease may have slipped last year (again, because of lots of overwintering inoculum). The primary inoculum for this pathogen generally comes from overwintering structures of the fungus that are lodged within cracks in the bark of cordons and trunks. Spring rain periods of at least 0.1” of precipitation and temperatures of 50 F or more, are the requirements for release of primary inoculum (ascospores) from the overwintering structures. The more mildew that was allowed to develop the year before, the larger the release of spores in early spring, the more primary infections that are likely to occur, and the more critical the need to control the disease early. Sulfur, oils, monopotassium phosphate, and potassium bicarbonate materials can be good choices for mildew management early on. All of these materials can eradicate small existing powdery mildew infections on leaves and cluster stems. Most do not generally offer any protection from future infections and therefore work best if applied often. Sulfur is an exception, and has the added benefit of providing a week or more of protection against future infections. Many of the more experienced growers like to utilize a mancozeb/sulfur combination to control all diseases during the pre-bloom period. This combination is relatively inexpensive, there are no resistance issues, and it works. Remember to read labels and be aware that you can’t mix sulfur and oils, or oils and captan. The tebuconazole products can be used during early pre-bloom to control powdery mildew as well, especially at the 8-10” shoot stage. These materials are very inexpensive and generally provide enough powdery mildew control to keep vines healthy until the immediate pre-bloom spray (they will also nicely control early black rot infections). At immediate pre-bloom and first post bloom, you want to apply your best powdery mildew chemistries like quinoxyfen (Quintec), difenoconazole (Revus Top), metrafenone (Vivando), fluopyram/tebuconazol (Luna Experience), etc. For native juice grapes, powdery mildew is rarely a concern during the early shoot growth stages, especially in the cooler Lake Erie region of Pennsylvania.

A note about fungicide resistance management and powdery mildew: It’s important to plan your powdery mildew management choices ahead of time with resistance management in mind. The easiest way to do this is to become familiar with FRAC (fungicide resistance action committee) codes listed prominently on the first page of fungicide labels. Fungicides with the same FRAC group number can be considered similar enough in their mode of action/chemistry that resistance to one is resistance to all others within that group. Therefore when you rotate fungicides for resistance management, you’re essentially rotating FRAC groups. Some good rules to remember are to avoid using the same FRAC group consecutively, or more than twice in a given season. The development of powdery mildew resistance is always a concern when using materials like the strobilurins (FRAC 11), the sterol inhibitors (FRAC 3), Quintec (FRAC 13), Vivando (FRAC U8), Luna Experience (FRAC 7, 3), Torino (FRAC U6), and Endura (FRAC 7) to name a few. Resistance is generally not a concern for uses of sulfur, oils, bicarbonates, and the potassium salts (mentioned above), or copper.

Next, black rot: One of the best ways to reduce overwintering inoculum of black rot is to scout your vineyard for old fruit mummies and eliminate them from the trellis. Black rot infected fruit mummies that have overwintered in the trellis are the most potent source of inoculum for infections the following spring. No matter how cold it gets over the winter, the pathogen survives just beautifully in colonized fruit remaining in the trellis. But, dropping this inoculum source to the soil, allows microbial degradation/weathering to reduce the potential for mummies to release spores the following spring. It also places the inoculum source much farther from new, susceptible plant tissue up in the trellis. The best time to ‘sanitize’ the trellis is during dormant pruning; weathering has already accomplished some of the removal of last season’s infected fruit from the trellis, and what remains is relatively easy to see and remove by hand. Experiments we conducted several years ago clearly showed that the earlier the mummies are knocked to the ground during the dormant period, the more time for decomposition to break them down before the next season, and the fewer spores released from the ground the following spring to start new disease cycles. Nevertheless, some inoculum on the ground will survive to release spores in spring, and burial of mummies with cultivation will go a step further to eliminate the threat. Removal of ALL old cluster material from the trellis before bud break is important to maintaining good control of this disease.

It may not be necessary to apply a fungicide for black rot at early shoot stages IF good control of this disease was achieved the previous year AND conscientious scouting and trellis sanitation has been implemented. However, the importance of early shoot infections should not be underestimated as I mentioned above, especially if they result in leaf lesions in the fruit zone. For example, inoculations we performed from early May to early June (simulating wet weather and an overwintering inoculum source (mummies) in the trellis) resulted in leaf and shoot lesions in the cluster zone (Figure 3). Those lesions went on to release spores during the critical fruit protection period, resulting in crop loss of 47-77% on those shoots with infected leaves!

An application of mancozeb, ziram, or captan for Phomopsis will also provide control of early black rot infections. The sterol inhibitor fungicides and strobilurins are also good materials for black rot that are more rainfast than mancozeb, ziram, and captan. The sterol inhibitors also provide excellent post infection activity that can be very useful at terminating an infection that has already occurred (but not yet manifested itself).

Figure 3. Early (pre-bloom) black rot leaf infections in the cluster zone provide inoculum that can add to problems with controlling fruit infection after capfall. The two small tan lesions on the leaf at node 2 are just inches from the developing inflorescence found at node 3 (picture on the right). These lesions will release spores during rainfall periods that could easily be splashed to highly susceptible cluster stems pre-bloom, and developing fruit after capfall. Resulting fruit infections will lead to crop loss.

Downy mildew and the 5-6 leaf stage: This stage marks the point at which the downy mildew pathogen first becomes active and is capable of releasing primary spores from inoculum sources that have overwintered on the ground (leaves and other plant material that was infected during the previous season). As with all other diseases, vineyards that developed a fair amount of downy mildew leaf/cluster infection last year will be at higher risk this spring than vineyards that were kept clean. However, overwintering structures of the downy mildew pathogen can survive more than one season in the soil.

Periods of rainfall with temperatures of at least 52 F meet the requirements of spore release and the first infections; plant surfaces must be wet for infection to occur. While scouting for this disease, expect to see it first in wetter areas of your acreage and pay close attention to leaves near the ground (sucker growth, grape seedlings that germinated from shelled berries last fall) which are most likely to become infected first. Therefore, keeping such low growth to a minimum in spring is a prudent control measure that can delay the development of the disease. It also suggests that if you’re planning vine trunk renewal from sucker growth, you will need to apply fungicides to protect that growth from the ground up as the pathogen becomes active.

Spring leaf infections are identified by the yellow ‘oil-spots’ seen on the tops of leaves (Figure 4), coinciding with white, downy sporulation of the pathogen on the undersides of leaves. Inflorescences can be blighted and show sporulation as well. Sporulation occurs during darkness under high relative humidity, and can typically be seen during a morning scout of the vineyard following a wet/humid night. Under optimum temperatures (70-75F), only an hour or two of plant surface wetness may be required for infection to occur, and new infections can produce their own spores with just 5 days.

Many parts of the northeast experienced drought conditions last year, which severely inhibited the development of this disease. Up in Erie County PA, the disease basically took a vacation in 2016, and I could barely find a handful of lesions on unsprayed ‘Chancellor’ leaves and fruit near the ground all summer: it was the perfect year to start renewal trunks! It wasn’t until later in August that rains finally returned and we began to see a few more infections, but for the most part the disease literally could not get off the ground in Erie county PA in 2016. What does this mean for 2017? The great lack of downy mildew in drought hit areas last year means that pre-bloom disease cycles this year will have to rely on overwintering inoculum from previous years (although spores of downy mildew can travel long distances between vineyards, the first infections will arise from inoculum within your vineyard). I have not found any detailed information as to how long the pathogen can survive in the soil, but I guarantee that if you’ve had downy mildew before, then it’s still there. Whether your area was wet or dry last spring, the principle described earlier still applies: vineyards devoid of downy mildew last year (whether from drought or just plain good control) will be easier to keep ‘clean’ in the pre-bloom period this year.

Mancozeb products are good options for the first downy mildew, Phomopsis, and black rot sprays in the pre-bloom period. Ziram and Captan have a similar spectrum of control, but Ziram is a little weaker on downy mildew, and Captan a little weak on black rot.  However, these may be a viable option if these diseases are not a huge threat early on (that is if you had good control last year). These materials are all surface protectants subject to wash-off by rainfall, which means that under heavy, frequent rainfall conditions, application intervals will need to be minimized (7-10 days?) especially for highly susceptible varieties. For that more critical ‘immediate pre-bloom’ spray (and the first post bloom spray), there are other materials like Presidio, Revus, Revus Top, and Zampro that are quite rainfast, very effective, and will provide longer range protection under wet conditions (when you need the protection most and are least likely to be able to stick to shorter spray intervals). However, products like Presidio also require a second active ingredient (like mancozeb) in a tank mix for resistance management purposes (which isn’t a bad idea at this critical spray timing in any case). Other materials like the phosphonates, Ranman, and the strobies /Reason, are probably best utilized outside the critical two sprays around bloom (especially for V. vinifera and highly susceptible hybrids), unless they’re used as tank mix partners with other effective materials. They’re very good materials, but they’re just not the ‘best of the best’.

Figure 4. Yellow oil-spot symptoms of downy mildew on young spring leaves.

One more time for emphasis: the immediate pre bloom and first post bloom (7-14 days later) fungicide applications are the most important you’ll make all year, regardless of variety grown and disease pressure. These two sprays protect your fruit from all the major fungal diseases (Phomopsis, black rot, downy and powdery mildew). Make sure sprayers are properly calibrated and adjusted for best coverage on a bloom-period canopy, spray every row at full rates and shortest intervals, and NEVER extend the interval between these sprays beyond 14 days.

‘Newer’ Fungicides: Aprovia (solatenol) may be worth a try for powdery mildew control (received federal registration in 2015). The active ingredient is related (same FRAC group) to Boscalid (found in Endura and Pristine) and Fluopyram (found in Luna Experience). It also has activity against black rot, but should not be expected to control this disease under high pressure on a susceptible variety.

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Social microbes and Schizosaccharomyces pombe

By Erika Szymanski of  The Winoscope

If there’s been a theme to the wine microbiology research of the past few years, it’s been microbial communities. Don’t just study one yeast or bacteria at once; look at an environment’s microbial population. And if there’s been a supporting theme, it’s been non-Saccharomyces yeast. Don’t just look at Saccharomyces cerevisiae; pay attention to at least some of the other, marginalized members of the microbial community, and ask what they can do for you.

Those two themes are obviously related. Studying microbial communities means noticing all of the auxiliary players in the environment. Noticing those players usually leads to asking what they’re doing and then to asking how you can exploit them. In another way, though, those two themes don’t overlap half often enough. Plenty of studies of non-Saccharomyces organisms keep on plodding on in the old microbiology tradition of poking and prodding at one or a few species as though they’ll work alone outside the lab.

Very forgivable in one sense. When we don’t know much about an organism in the first place, sussing out its individual characteristics before querying how it behaves in mixed company doesn’t seem unreasonable. It’s also fair to say that plenty of winemaking involves making an effort to kill all existing microbes before inoculating one selected S. cerevisiae strain that’s supposed to work alone. Then again, single-microbe studies remind me of studies of individual primates held in solitary captivity, which are not only deeply unethical but not very useful. What primate, humans included, is going to behave normally when held in solitary confinement? I’m not claiming that solitary microbe studies are unethical, or that they do harm to the microbes involved, but we have plenty of evidence that microbes are social.* Data from solitary confinement studies is limited.

So a new study on Schizosaccharomyces pombe is heading in an interesting direction, but yields data with some limitations for winemaking.

Is S. pombe a spoilage organism? That’s like asking whether dandelions are weeds: yes, in the lawns of a golf course; no, when you’re growing them for salad greens. S. pombe produces unpleasant quantities of acetic acid. It also efficiently (and even completely) metabolizes malic acid. Scott Labs sells S. pombe“teabags” that can be dropped into overly acidic tanks or barrels and then fished back out again, after malic acid has been degraded but before volatile acidity gets out of hand. New research (open-access article) has considered whether some S. pombe strains, carefully selected for low acetic acid production, might be suitable as primary fermentation organisms to be used instead of S. cerevisiae rather than afterwards. The team was able to find several low acetic-producers, able to ferment a must to dryness (albeit they tested final alcohol concentrations in the 12-12.5% range), and still able to simultaneously metabolize malic acid. Their perfunctory sensory testing, however, pretty much only judged for major faults: acidity, reduction, acceptable aroma. So when the researchers conclude that these strains might be a good option for high-acidity musts instead of malolactic fermentation, they’ve yet to account for whether that solution produces a delicious product or merely an acceptable one. Still, these strains might be incredibly useful in combination, or when a vat of something undrinkably acidic needs to be made inoffensive enough to be blended away into something else. But how do these microbes behave in company, when asked to cooperate on the job of making a drinkable wine?

I hope that this project steps forward in two directions. One: better sensory analysis. Two: what happens when S. pombe and S. cerevisiae (and perhaps some other bugs) are asked to play together.

*The Foster Lab at Oxford is up to interesting research on cooperation between microbes and other species. Here’s another (albeit dated; 2007) excellent resource on microbial sociability, from Annual Reviews in Ecology, Evolution, and Systematics. Unfortunately, it’s also behind an academic publisher’s paywall.

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Reviewing YAN and Hydrogen Sulfide: Part 2

By: Denise M. Gardner

In a previous post, we discussed ways in which nutrient management during primary fermentation can affect hydrogen sulfide formation and the overall “health” of the wine.  This week, we’re going to explore how to mediate hydrogen sulfide aromas and flavors in a finished wine.

Sulfur-Containing Off Aromas

In general, many wine sensory scientists and wine experts will agree that is relatively a bad habit to use the term “sulfur” to describe off-odors associated with hydrogen sulfide or “stinky” aromas that are usually described by the term “reduced.”  One of the main arguments for avoiding “sulfur” as a description term for an aroma is due to the fact that there are actually several forms of aromatic sulfur-containing compounds found in wine, and they can have very different aromas (smells, odors) associated with that one compound.  The most common groups of aromatic sulfur-containing compounds in wine are:

  • Sulfur dioxide (SO2)
  • Hydrogen sulfide (H2S)
  • Mercaptans or Thiols
  • Disulfides

Additionally, many sensory experts will advise further to avoid using the chemical names as descriptors for describing an aroma found in wine (e.g., using the term “hydrogen sulfide” to describe the hard-boiled or rotten egg aroma).  It is typically recommended to use an actual descriptor when describing an aroma (e.g., using the term “rotten eggs” when that smell exists in wine).

Sulfur Dioxide (SO2)

Sulfur dioxide is an antioxidant and antimicrobial preservative frequently used in wine production.  However, it is also produced by yeast during primary fermentation, which is why wines (and other fermented products) cannot be sulfur dioxide-free (commonly referred to as “sulfite free” in the mass media).  The aromatic descriptor commonly associated with a high concentration of sulfur dioxide is termed “burned match,” but a high concentration of sulfur dioxide can also cause a nasal irritation that many will describe as nasal burning.

Hydrogen Sulfide (H2S)

Hydrogen sulfide is an aromatic compound that is commonly described as having a “rotten egg” or “hard-boiled egg” aroma.  Like many sulfur-containing compounds, hydrogen sulfide has a low sensory threshold (<1 – 1 part per billion, ppb), indicating that about 50% of the population could sense this compound at that concentration without being able to identify it, specifically, as hydrogen sulfide.

As we saw in our previous post, hydrogen sulfide development can result as a component of poor nutrient management during primary fermentation.  Residual elemental sulfur from pesticide sprays has also been linked to latent development of hydrogen sulfide in wines.  In a 2016 edition of Appellation Cornell, Dr. Gavin Saks’ lab provided a detailed and practical report on how hydrogen sulfide can be a problem for winemakers post-bottling and the potential links to hydrogen sulfide development as a function of residual sulfur from the vineyard (Jastrzembski and Saks, 2016).

Occasionally, winemakers may also experience hydrogen sulfide formation during a sur lie aging period; a time in which the finished wine remains on the lees when lees are stirred in the wine.  It is also common for sparkling wines, produced in the traditional method, to exhibit a small perception of hydrogen sulfide when the bottle is first opened.

Mercaptans/Thiols and Disulfides

Finally, mercaptans or thiols, sulfur-containing compounds that contain the functional group –SH, and disulfides, sulfur-containing compounds that contain a S-S bond, can also be problematic for winemakers when found at high concentrations.

The presence of sulfur-containing volatile compounds is not always considered detrimental to wine quality.  For some wine grape varieties (e.g., Sauvignon Blanc), these classes of compounds can make up their varietal aroma.  In very small concentrations, sulfur-containing compounds can also be aroma enhancers, indicating that their presence can actually make the wine smell fruitier than if they were not present in the wine.  However, when at substantial concentrations, volatile sulfur-containing compounds can also produce various “stink” aromas that mask a wine’s fruitiness, freshness, and make the wine generally unappealing.  This is phenomena is dependent on the concentration of the sulfur-containing compound and the chemical makeup of the solution (i.e., wine) it is in.

Mercaptans or thiols and disulfides have a variety of descriptors associated with them, and their perception is largely based on concentration.  When we’re discussing the negatively-associated descriptors, common terms include: garlic, onion, canned asparagus, canned corn, cooked cabbage, putrefaction, burnt rubber, natural gas, and molasses amongst others.

Are There Sulfur-Containing Off-Aromas in Your Wine?

To identify if hydrogen sulfide, mercaptans/thiols, or disulfide-based off-odors exist in your wine, it may be best to use a copper screen as a bench trial.  While analytical identification of these compounds is possible, it is often expensive and leaves the winemaker guessing on what to do next.

For a quick assessment of a wine’s aroma, winemakers can drop 1-2 pre-1985 copper pennies into a glass of wine to see if the aroma freshens.  The freshening aroma is due to the fact that the copper from the penny is reacting with the sulfur-containing compounds in the wine and making them aromatically inactive.

The "penny test" is often used to quickly determine if a wine is suffering from reduction, the presence of several types sulfur-containing off-odors. Photo by: Denise M. Gardner

The “penny test” is often used to quickly determine if a wine is suffering from reduction, the presence of several types sulfur-containing off-odors. Photo by: Denise M. Gardner

A technical copper screen takes a bit more work and should be conducted in a quiet and aromatically-neutral environment.  It is recommended to do this outside of the cellar.

Copper addition, in the form of copper sulfate, is often used to remediate aromas/flavors associated with hydrogen sulfide. One-percent and 10% copper sulfate solutions can be purchased through your local wine supplier.  The basic protocol associated with a copper screen is as follows:

  1. Add 50 milliliters of wine to two glasses.
  2. Label one glass “control” and the other “copper addition” (see image below).
  3. Add 1 mL of 1% copper sulfate to the “copper addition” glass.
  4. Cap both glasses for 15 minutes.  Sniff the aroma of each wine.

Setting up a copper screen can help determine if a wine is suffering from aromas caused by sulfur-containing compounds. Photo by: Denise M. Gardner

Setting up a copper screen can help determine if a wine is suffering from aromas caused by sulfur-containing compounds. Photo by: Denise M. Gardner

Sniff (smell only!) both glasses. Most people start with the “control” and smell the treated wine (wine containing copper sulfate) second.  If the aroma/flavor of the “copper addition” glass has improved, or the hydrogen sulfide aroma has subsided, then a copper addition trial should follow to determine the exact concentration of hydrogen sulfide needed to clean up the wine in question.  Remember that the legal limit for copper allowed in a finished wine is 0.5 ppm.

Treatment of Sulfur-Containing Compound Off-Aromas

Sulfur-containing compounds are quite reactive, which can make dealing with them fairly difficult.  Many educators agree that the best way to treat sulfur-containing compounds, especially those that stink, is to prevent their existence as best as possible.

In the Appellation Cornell newsletter that focused on sulfur pesticide residues, Jastrzembski and Saks (2016) recommended that sulfur residue concentrations should not exceed 1 mg/kg at harvest in order to avoid latent hydrogen sulfide or sulfur-containing off-aromas later in processing and storage.  Additionally, many experts recommend appropriately treating fermenting musts with nutrient management strategies based on the starting YAN concentration to minimize the incidence of hydrogen sulfide formation during primary fermentation.

As described above, winemakers may also opt to treat the wine with copper sulfate to try to reduce the perception of hydrogen sulfide or other sulfur-containing aromas.  It should be noted that aromas caused by disulfides cannot be mediated with a copper sulfate addition.

There has been more conversation in the academic community regarding the reemergence of hydrogen sulfide or sulfur-containing off-aromas after a wine has been treated with copper and post-bottling.   The theory around this appears to circulate around residual copper initiating reactions in the wine that lead to more sulfur-containing off-odors.  This continues to be an ongoing discussion amongst researchers and will likely be a hot topic within with the wine industry.  For now, it is important for winemakers to understand that there may be a risk of off-odors reemerging post-copper treatment and post-bottling.  This topic will also be discussed to some degree at the 2017 PA Wine Marketing and Research Board Symposium on March 29, 2017 in State College, PA, and winemakers are encouraged to attend.

Some hydrogen sulfide or sulfur-containing off-odors can sometimes be mediated with use of fresh lees stirred in the wine or the addition yeast lees-like products.  Winemaking products like Lallemand’s Reduless, yeast hulls, or some cellulose-based products can help reduce or eliminate the intensity of these off-odors.  As with any other product additions, it is recommended that wineries always do bench trials first and before adding to the entire volume of wine.  Additionally, Enartis USA (Vinquiry) has previously distributed a fact sheet to help winemakers troubleshoot reduced wines and determine how to best treat a problem wine.

The incidence of reduction, sulfur-containing off-odors, or hydrogen sulfide can be a frustrating circumstance for winemakers.  However, adequate vineyard care and proper nutrient management during primary fermentation can help minimize the incidence rate of sulfur-containing off-odors from occurring in their wines.  Of course, problems with wines do occur, and we hope that the recommendations above will help winemakers solve wine problems pertaining to sulfur-containing off-odors.

 

Resources

Jastrzembski, J. and G. Sacks. 2016. Sulfur Residues and Post-Bottling Formation of Hydrogen Sulfide. Appellation Cornell, 3a.

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Reviewing YAN and Hydrogen Sulfide: Part 1

By: Denise M. Gardner

Yeast assimilible nitrogen (YAN) is the sum of the amino acid and ammonium concentrations available in the grape juice at the start of fermentation.  Typically, the amino acid proline is not included in the reported amino acid content as it is not readily utilizable by yeast cells.

The amino acid component of YAN is often referred to as the “organic” YAN form.  In contrast, the ammonium ion content is referred to as the “inorganic” YAN form and may be written in its ionic abbreviation: NH4+.  Due to the fact that ammonium is only connected to a series of protons (H+ions), it tends to be easier to move in and throughout the yeast cell to be consumed during fermentation (Mansfield, 2014). When these two components (organic + inorganic) are added together, the resultant value is the YAN, written with the units: mg N/L.

The winemaking challenge associated with YAN is the fact that it is quite variable, and current research has not identified ways to change the YAN, predictively, in fruit through the manipulation of vineyard practices.  YAN varies by vintage year, grape variety, cultivar, and with the use of various vineyard management practices.  In Penn State’s research vineyards, ~1 acre in size and containing 20 different wine grape varieties, YAN values ranged dramatically each vintage year amongst the various wine grape varieties.  On any given vintage year YAN values ranged from low (<100 mg N/L) to high (>300 mg N/L) amongst the varieties grown in that one site.

The variability associated with YAN provides a secondary challenge to winemakers: the lack of predictability associated with hydrogen sulfide formation during primary fermentation due to unfulfilled nitrogen needs by wine yeasts.

What does YAN have to do with Hydrogen Sulfide?

Winemakers often talk about YAN in relation to hydrogen sulfide (H2S) as the two have been associated with one another throughout primary fermentation.  Although there are several potential causes of hydrogen sulfide formation during wine production, some of which we will talk about in our Part 2 series, nitrogen imbalance has been one of the factors that winemakers can influence through production.  Unfortunately, there is no way to ensure that a wine will not produce hydrogen sulfide by the end of fermentation, but treating wines with proper nutrient supplementation can help minimize the incidence of hydrogen sulfide production during primary fermentation.

Hydrogen sulfide is produced by the yeast cell via the sulfate reduction pathway (Figure 1).  While I know this figure looks scientifically daunting, we can try to simplify its purpose to discuss how hydrogen sulfide is released into wine.  Sulfate (SO42-), naturally abundant in grape juice (Eschenbruch 1974), is transported into the yeast cell for amino acid (cysteine and methionine) development, which are naturally lacking in concentration in grape juice (Bell and Henschke, 2005).  Energy is used by the yeast (represented as ATP in Figure 1) to chemically alter the structure of sulfate in order to make it useable by the yeast cell.  This useable form can be seen as sulfide (S2-) in the image below.  Using nitrogen, which is required to make an amino acid, the sulfide content is depleted as cysteine and methionine amino acids get produced.  Therefore, as sulfide reserves are depleted, cysteine and methionine contents generally increase to be used for building proteins that will be needed by the existing or new yeast cells.

Figure 1: A simplified version of the sulfate reduction pathway.

Figure 1: A simplified version of the sulfate reduction pathway.

Sulfur dioxide (SO2) plays a role in the sulfate reduction pathway in that it bypasses the transport mechanism required to bring sulfur into the yeast cell.  It other words, it can diffuse across the cell membrane and into the internal parts of the yeast cell.  Sulfur dioxide will get chemically altered to be made into the useable sulfide , S2-, form as well.  Therefore, fermentations that contain a high concentration of sulfur dioxide at the start of fermentation have the potential to increase the utilization of sulfur dioxide during yeast metabolism.

These processes function normally until a depletion of nitrogen (from the nitrogen pool) or an accumulation of sulfide develops in the yeast cell.

If there is not enough nitrogen (low YAN fermentations) available to make the sulfur-containing amino acids (cysteine and methionine) then, eventually, the yeast cell will not be able to continue manufacturing these amino acids.  In this situation, the sulfide concentration generally starts to increase within the yeast cell.

The chemical form sulfide, however, is toxic to the yeast cell and thus, the yeast will try to eliminate it from its internal structures.  Therefore, when sulfide concentrations get too high, the yeast will diffuse this across its cell membrane into the surrounding media: the fermenting juice.  When hydrogen sulfide concentrations get high enough in the fermenting juice, winemakers can often sense the rotten or hardboiled egg aroma associated with the compound.

What if there is too much nitrogen?

In contrast, too much nitrogen (high YAN fermentations) can also be problematic.  Higher concentrations of the inorganic component of YAN can lead to a high initial biomass (population) of yeast.  The rapid increase in yeast populations can lead to nutrient starvation by a majority of the yeast when the wine is about almost finished completing fermentation.  With a large biomass of yeast incapable of obtaining the proper nutrient (nitrogen) content to grow and reproduce, hydrogen sulfide development can result.  This is due to the fact that there is a large population of yeast in situations in which there is not enough nitrogen to support their growth (i.e., there is not a lot of food to go around for all of the yeast cells).  With hydrogen sulfide development occurring late in primary fermentation, it is obvious that the winemaker would become concerned with hydrogen sulfide retention by the time fermentation is fully complete.

Too much nitrogen can also cause other quality problems.  Due to the excess amount of available nutrients, yeast can grow and reproduce quickly, which often leads to very rapid or very hot fermentations.  The speed of fermentation, of course, can affect the aromatics and quality of the wine (i.e., fast fermentations often lead to simpler aroma and flavor profiles).  This may not be an issue with some styles of wine, but for many white wine or fruit (other than grapes)-based fermentations, aromatic retention is often a priority by the winemaker.

Due to the fact the initial YAN is so high, all of the nitrogen contents may not be utilized by the yeast population by the end of fermentation, and could remain in suspension in the finished wine.  As yeasts begin to autolyze, all of their inner components, including the remaining nitrogen content, will become available in the wine.  The excess “food” could be available for other microorganisms (like acetic acid bacteria, lactic acid bacteria, or Brettanomyces), which could potentially lead to spoilage problems if the wine is not properly stabilized.  Such spoilage is, obviously, detrimental to wine quality and undesirable by the winemaker.  Alternatively, remaining nutrients could be utilized by malolactic bacteria or those wines that will be given tirage for sparkling production (Bell and Henschke, 2005).

Finally, higher YAN concentrations can lead to an increased risk of ethyl carbamate production in wine; ethyl carbamate is a known carcinogen that can give susceptible individuals headaches, or even respiratory illness.  Ethyl carbamate is produced in a reaction between ethanol and urea (Bell and Henschke, 2005).  The heavy use of DAP has also been linked to a higher potential risks of ethyl carbamate due to the fact that DAP inhibits the transport of amino acids into the yeast cells, and therefore, leaves a higher concentration of amino acids available that can potentially be altered into urea, a precursor for ethyl carbamate (Bell and Henschke, 2005).

The fact that excess nitrogen can be problematic during wine production should provide insight to winemakers to avoid over-supplementing their fermentations.  Hence, it is often recommended to that winemakers measure and identify their starting concentration of YAN and supplement accordingly.

Nitrogen Supplementation

Nitrogen (nutrient) management and supplementation is not uncommon during primary fermentation as nutrients are an important component of yeast cell growth and metabolism.  In the yeast cell, nitrogen is a required nutrient in the synthesis of amino acids and to build proteins that are used in the yeast cell walls and organelles, as discussed above.  Without protein development, the yeast cell cannot live.

Winemakers can supplement their fermentations with nitrogen by adding nutrient supplements in the form of:

  • Hydration nutrients (e.g., GoFerm, Nutriferm)
  • Complex nutrients (e.g., Fermaid K, Nutriferm)
  • Diammonium phosphate (DAP)

DAP is considered an inorganic form of nitrogen, while the complex nutrients may contain additional organic yeast components that contribute organic forms of nitrogen.  Recall, above, that the inorganic form of nitrogen is more readily consumed by yeast, and it can be easily absorbed by yeast cells even as alcohol concentrations rise during primary fermentation.  Amino acids, on the other hand, require energy expenditure in order to be brought into the cell through transport proteins located on the cell membrane.  The presence of both alcohol and ammonium ions inhibit the transfer of amino acids from the juice into the yeast cell (Santos, 2014).  Therefore, it is often recommended to avoid the addition DAP or products that contain DAP (i.e., Fermaid K, Nutriferm Advance) at inoculation and until after yeasts have the opportunity to best absorb amino acids.

Starting YAN Concentrations

Nonetheless, nutrient supplementation strategies are often based on starting YAN concentrations in the fruit.  Due to the regular variability of YAN concentrations, winemakers are encouraged to measure YAN for each lot of grapes every year.  This is often problematic for winemakers whom do not have the time to run the appropriate analyses associated with YAN or the financial resources to send samples to an analytical lab.  Such challenges force many winemakers into a situation in which all fermentation lots are treated with the same repeated nutrient supplementation regardless of the starting concentration of YAN.

In previous Extension workshops, research from Cornell University on Riesling wine grapes found that they could accurately predict the harvest YAN when good field samples were taken within 2 weeks from harvest (Nisbet et al., 2013).  In 2016, Cornell released a second publication that focused on YAN prediction models for Cabernet Franc, Chardonnay, Merlot, Noiret, Pinot Noir, Riesling, and Traminette.  While the prediction models were not recommended for regions outside of the Finger Lakes (where the data was sourced from for this study), they found that in some cases, YAN data could be obtained within 5 weeks of harvest (Nisbet et al., 2014).  This extra flexibility in time can aid in obtaining accurate YAN results before the grapes reach the crush pad, which ultimately helps winemakers prepare for nutrient supplementation before the start of fermentation.

Until further research can provide predictive modeling for other wine regions, it is generally accepted that winemakers should measure YAN at or as close to harvest as possible.

YAN can be measured using the following the analytical procedures:

  • Enzymatic methods for both primary amino acids and ammonium.
  • Probe for ammonium ions.
  • Formol titration

While the Formol titration is often preferred by many small wineries due to the lower start-up investment, the use of formaldehyde, a known carcinogen and lung irritant, in this protocol does require some consideration for laboratory safety.  Additionally, the proper disposal of formaldehyde, a hazardous substance, can be an issue for many wineries.

Enzymatic methods by spectrophotometer definitely require a bit of experience in order to become more efficient in their use, which can be problematic for those operations that find measuring YAN too timely.  Additionally, enzymatic kits have to be purchased fresh and have a small shelf life.  The advantage of investing in a spectrophotometer, however, is that other enzymatic kits can be purchased to measure additional wine components including residual sugar, malic acid, and acetic acid.

Nonetheless, measuring YAN should be a consideration for wineries that struggle with hydrogen sulfide aromas by the end of primary fermentation.  It is through the starting numerical value that winemakers can better manage and adjust nutrient supplementation strategies to help minimize the reoccurrence of hydrogen sulfide at the end of fermentation.

Nutrient availability during primary fermentation is only one potential contributor to hydrogen sulfide formation in wines.  In the next blog post, we’ll explore other potential causes of hydrogen sulfide formation and how to best mediate the problem when it exists.

 

References

Eschenbruch. R. 1974. Sulfite and sulfide formation during winemaking – a review. Am. J. Enol. Vitic. 25(3): 157-161.

Bell, S.-J. and P.A. Henschke. 2005. Implications of nitrogen nutrition for grapes, fermentation and wine. Aust. J. Grape and Wine Res. 11:242-295.

Mansfield, A.K. Are you feeding your yeast?: The importance of YAN in healthy fermentation. Webinar. Feb. 2014.

Nisbet, M.A., T.E. Martinson, and A.K. Mansfield. 2013. Preharvest prediction of yeast assimilable nitrogen in Finger Lakes Riesling using linear and multivariate modeling. Am. J. Enol. Vitic. 64(4): 485-494.

Nisbet, M.A., T.E. Martinson, and A.K. Mansfield. 2014. Accumulation and prediction of yeast assimilible nitrogen in New York winegrape cultivars. Am. J. Enol. Vitic. 65(3): 325-332.

Santos, J. Getting Ready for Harvest: Yeast Nutritional Needs. Workshop Seminar. July 2014.

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