It’s that time of year again: bottling time! The past year’s vintage is slowly starting to take up too much room in the cellar and now is the time for decision making in terms of preparing for the pending vintage. Finalizing a good bottling schedule before harvest starts is an essential good winemaking practice, but bottling comes with its own set of challenges.
It is not uncommon for winemakers to express feelings of “not being able to sleep at night” when wines get bottled, as they are worried about possible re-fermentation issues. As wine naturally changes through its maturity, it is easy to feel insecure about bottling wines, especially those wines that may have had challenges associated with it throughout production.
However, there are several analytical tests that winemakers can add to their record books every year to ensure they are bottling a sound product. The following briefly describes a series of analytical tests that provide information to the winemaker about stability and potential risks associated with the product when it goes in bottle.
Bottling comes with its own set of challenges and risks, but several analytical tests can help put a winemaker’s mind to ease regarding bottle stability. Photo by: Denise M. Gardner
Basic Wine Analysis Pre-Bottling:
This first list is the bare minimum data that should be measured and recorded for each wine getting bottled, regardless of the wine’s variety or style. Keeping accurate records of these chemistries is also helpful in case something goes wrong while the bottle is in storage or after it is purchased by a customer.
pH is essential to know as it gives an indication for the wine’s stability in relation to many chemical factors including sulfur dioxide, color, and tannin. For example, high pH (>3.70) wines provide an indication that more free sulfur dioxide is needed to obtain a 0.85 ppm molecular free sulfur dioxide content. At the 0.85 ppm molecular level, growth of any residual yeast and bacteria in the wine should be adequately inhibited.
High pH wines tend to have issues with color stability. At this point, color stability can be addressed by blending or with use of color concentrates (e.g.,Mega Purple). Keep in mind that if the wine is blended with another wine, all chemical analyses, including pH, should be completed on the blend (as opposed to average individual parts) prior to bottling.
Free and Total Sulfur Dioxide Concentration
In the United States, total sulfur dioxide is regulated and must fall under 350 mg/L for all table wines (CFR: https://www.ecfr.gov/cgi-bin/text-idx?SID=eddaa2648775eb9b2423247641bf5758&mc=true&node=pt27.1.24&rgn=div5#sp27.1.24.a).
However, the free sulfur dioxide concentration provides an indication to the winemaker regarding antioxidant strength and perceived antimicrobial protection. To inhibit growth of yeast and bacteria during bottle storage, a 0.85 ppm molecular free sulfur dioxide concentration must be obtained. The free sulfur dioxide concentration required to meet the molecular level is dependent on pH. Therefore, free sulfur dioxide additions should be altered and based on a wine’s pH for optimal antimicrobial protection.
Analytically, it can be daunting to measure free sulfur dioxide as the wet chemistry set up looks intimidating. However, many small commercial wineries have benefited from the integration of a modified aeration-oxidation (AO) system, and with a little practice, have been relatively successful at monitoring free sulfur dioxide concentrations. A few wineries have worked to validate use of Vinmetrica’s analyzer (https://vinmetrica.com/), and found results comparable to those obtained by use of the AO system.
Residual (or Added) Sugar
Any remaining sugar in the bottle, whether through an arrested fermentation or direct addition, can pose a risk for re-fermentation post-bottling. This is especially true if the winery lacks good cleaning and sanitation practices. Nonetheless, it is a good idea to assess the sugar content pre-bottling to record a baseline value of the sugar concentration going into bottle. If bottles were to start re-fermenting, a sugar concentration could be analyzed and used to compare against the baseline value in order to assess the potential of yeast re-fermentation.
For wineries with minimal residual sugar concentrations, a glucose-fructose analysis (often abbreviated glu-fru) is often used to help determine accurate sugar content. For wines with added sugar an inverted glucose-fructose analysis may be required.
If you are concerned about potential risk for Brettanomyces (Brett) bloom post-bottling, it is usually encouraged to reduce the sugar content in the finished wine below 1% (<10 g/L sugar) in the bottle.
Malic Acid Concentration
While using paper chromatography to monitor malolactic fermentation (MLF) is useful, it does not give an accurate reflection of residual malic acid concentration. In fact, some winemakers find that a paper chromatogram may show a MLF has been “completed,” but would prefer to have lower residual malic acid concentrations remaining in the wine.
During my time at an analytical company, 0.3 g/L of malic acid and below was considered “dry.” This is typically a safe level of residual malic acid to avoid post-bottling MLF.
Volatile acidity (VA) is federally regulated, and levels are indicated in the Code of Federal Regulations (CFR: https://www.ecfr.gov/cgi-bin/text-idx?SID=eddaa2648775eb9b2423247641bf5758&mc=true&node=pt27.1.24&rgn=div5#sp27.1.24.a). For most states, with California as an exception, the maximum allowable VA for red wines is 1.40 g/L acetic acid (0.14 g/100 mL acetic acid) and for white wines is 1.20 g/L acetic acid (0.12 g/100 mL acetic acid).
Monitoring VA through production is a good indicator of acetic acid bacteria spoilage. At minimum, wineries should record VA
- immediately post-primary fermentation,
- periodically through storage (e.g., every 2-3 months) and
Whiling monitoring VA, sharp increases in VA should alarm the winemaker of some sort of contamination. Typically, these increases are caused by acetic acid bacteria, which can only grow with available oxygen.
As a general rule of thumb, knowing the final alcohol concentration is a good idea. Alcohol content helps determine a tax class for the wine and is required for the label.
Titratable Acidity (TA)
All wines are acidic in nature as they fall under the pH 7.00. However, titratable acidity (TA) acts as an indicator for the sour sensory perception associated with a given wine. For example, two wines, Wines 1 and 2, with a pH of 3.40 may have different TAs. If Wine 1 has a TA of 8.03 g/L tartaric acid while Wine 2 has a TA of 6.89 g/L tartaric acid, Wine 1 would likely taste more acidic (assuming all other variables are the same).
Titrations are an easy analytical testing method to learn and understand when testing wine’s chemistry. Photo by: Denise M. Gardner
Cold stability tests are often recommended to ensure the wine is cold stable, and will, therefore, not pose a threat of precipitating tartrate crystals during its time in bottle. Not all wines require a cold stability process (e.g., seeding and chilling). Cold stability testing can be done prior to a cold stabilization step in order to avoid extraneous processing operations, saving time and money.
For more information on cold stability processes and testing, please visit Penn State Extension’s website: http://extension.psu.edu/food/enology/analytical-services/cold-stabilization-options-for-wineries
These crystals on this cork illustrate what can happen when a wine is not properly cold stabilized. While the tartrate crystals pose no harm to consumers, they may find the crystals unappealing or questionable. Photo by: Denise M. Gardner
Additionally, haze formation is a potential risk post-bottling. While hazes do not typically offer any safety threat to wine consumers, they often look unappealing. Protein hazes tend to make the wine look cloudy. Some varieties are more prone to protein hazes then others, and running a protein stability trial could minimize the risk for a protein haze in-bottle.
It is important to remember that due to the fact protein stability is influenced by pH, cold stability production steps should take place before analyzing the wine for protein stability and before going through any necessary production steps to make the wine protein stable. This is due to the fact that cold stability processes ultimately alter the wine’s pH, and the chemical properties of proteins are influenced by the pH.
Analysis for Those that May Consider Bottling Unfiltered:
Yeast and Bacteria Cultures (Brett, Yeast, Lactic Acid Bacteria, Acetic Acid Bacteria)
Having a microscope in the winery can be a great reference point in terms of scanning for potential microbiological problems. However, if the winery does not have a microscope, but knows that some microbiological issues or risks may exist in a wine, having a lab set test the wine on culture plates is a good indicator for potential growth risks during the wine’s storage.
If the wine is going to be bottled using a sterile filtration step, keep in mind that wines are not bottled sterile. Assuming the absolute filtration method is working properly, the wine has potential to become re-contaminated with yeasts and bacteria from the point of which it exits the filter. In fact, it is not uncommon for wines to pick up yeast or bacteria contamination during the bottling process.
Managing free sulfur dioxide concentrations can help inhibit any potential growth from contamination microorganisms if the proper antimicrobial levels (0.85 ppm molecular) are obtained at that wine’s pH and retained during the bottle’s storage.
4-EP and 4-EG Concentrations for Reds
For wines that may have had a Brettanomyces (Brett) bloom, knowing the concentrations of 4-EP and 4-EG in the wine going into bottle is a good result to keep on file. If a Brett bloom occurs later in the bottle, it is likely (although, not guaranteed) that the volatile concentration of 4-EP and/or 4-EG may increase and confirm the problem.
Furthermore, evaluating a wine for 4-EP and 4-EG concentrations can also help isolate a possibility of Brett existence, especially if their concentrations are below threshold. However, it should be noted that both compounds can also exist in wines that are stored in wood, even without a Brettcontamination.
Double Check: PCR for Reds
Brett can be a tricky yeast to isolate and identify. It is usually recommended to run multiple analytical tests related to Brett in order to confirm its existence or removal from a wine. While culture plating identifies living populations of microorganisms, PCR cannot typically differentiate between live and dead cells as it is measuring the presence of DNA. A microorganism’s DNA can get into a wine after yeast death and through autolysis. Therefore, a positive PCR result for Brettanomyces is hard to confirm if the result includes live cells, dead cells, or a combination of both.
Culture plating can help confirm the presence of active, live cells, but the success rate of growing Brettanomyces in culture plates is variable.
Nonetheless, scanning wines by PCR for Brett can help winemakers isolate a general presence and risk of Brett in their wines.
Wine samples prepare for analytical evaluation. Photo by: Denise M. Gardner
Still Worried About Your Wine Post-Bottling?
Bottle sterility testing is helpful, especially when a winemaker wants to ensure wines have been bottled cleanly. For this type of testing, it is best to sample a few bottles
- at the beginning of a bottling run,
- immediately before any breaks,
- immediately after any breaks, and
- at the end of a bottling run.
Bottles can, again, be evaluated under a microscope and evaluated for the presence of microorganisms. Bottles can also be sent to a lab for culture plating. The growth of yeasts or bacteria from culture plates at this stage indicates a failure of the sterile filtration system or contamination of the wine post-filtration. Clean wines, obviously, should help put a winemaker’s mind at ease as it matures in bottle.
Ensuring a wine’s stability post-bottling is a challenge. However, with proper cleaning and sanitation methods coupled with the right analytical records, winemakers can reduce their worry. For information on any of these topics, please visit:
The strange and sometimes unorthodox tools that make our lives easier have tickled my imagination ever since I was a child. Gizmos and gadgets were always on the top of my wish list for birthdays and Christmas. I suspect this fascination was passed down to me from my dad. He always buys the latest tech on the market even though more than half of the stuff he buys ends up in his desk drawer gathering dust. But that is where my father and I differ a whole lot. I like to know that something is going to be useful to me before I buy it and besides, as a student, you don’t have money laying around to spend on white elephants. So now that I am a “grown-up” I am buying more “mature” gadgets or tools that I can use on a daily basis i.e. wine accessories. But with all the hundreds that you see in the shops and online, it’s difficult to figure what is useful and what’s not. Here are a few of my favourites and some of the Old faithfuls.
No one who calls themselves a wine enthusiast will be caught dead without a decent wine decanter. For those of you who are not quite in the know, a decanter is a container, usually made of glass (but plastic ones are now also available for picnics), that is used to aerate red wines (i.e. expose it to oxygen) and to separate the glorious liquid from it’s not so glorious solid sediments. Although it might not technically be a gadget, it is something that comes in quite handy if you have the in-laws coming over for dinner and you want to impress with a well-aged Cab, but all you have are robust, raunchy 2014s. A decanter will not only look impressive, but it will smoothen that Cab out in two ticks. And with the variety of shapes and sizes that are now readily available, your decanter can double as a unique piece of art, exhibited on your dining room table, 7 days a week.
For those of you that might be a bit clumsier and fear the day that your very expensive decanter falls to smithereens, a wine aerator is probably a better option. This nifty little gadget can be screwed into or attached on top of your opened wine bottle and as you pour it allows for better aeration of the wine. These accessories can also sometimes look overly extravagant or other-worldly, but even the simplest ones can help to simulate the effects of years of bottle aging in a flash.
Hot summer days calls for chilled Sauvignon blanc on the stoep or next to the pool, but you forgot to refrigerate the bottle in time or the Stellenbosch sun heats up your glass faster than you can finish your wine (I highly doubt it). No problem. You can just add some ice cubes. But the melting ice dilutes my wine, you say. Well, not anymore. Waterless, reusable ice cubes have arrived to save many wine and spirit drinkers lots of sorrows. These blocks and balls of pure genius can be rinsed, popped back in the freezer and used again and again. No dilution. These are of course also great for the next family picnic. No more carrying around a cooler box filled with ice water to keep mommy’s wine cold. They are fun for the whole family!
And if, for some reason, you don’t like ice or having things floating around in your glass, there is always the revolutionary corkcicle. Yes, you read correctly. Cork-icicle. It’s a long, insulated chill-stick that is attached to a bottle stopper or cork-like stopper. This magnificent piece of wine artillery will help to keep your whites cold and get your reds down to sub-room temperature. Make sure to reserve a spot for this in your picnic basket as well.
Speaking of picnics (as you might have guessed, I am a picnic enthusiast), isn’t it just the worst when you’ve just settled down on your blanket with your glass of chilled Chardonnay and somebody asks you to hand them the food basket. Where am I supposed to put down my wine, you might ask yourself. That is where my next item of interest comes in. Sturdy, stainless steel wine bottle and glass stakes that can be pinned into the ground will ensure that your glass stays upright and out of the grass.
The weekend and the picnics have passed. It’s Monday after work and you just feel like winding down with a glass of red, but the day wasn’t quite that bad that you want to finish the whole bottle yourself. What to do? “Reseal” your bottle after you’ve poured your glass with your wine pump, of course! The pump usually comes with a rubber stopper that is placed in the mouth of the bottle. The pump is then placed over the stopper to pump the air out either manually or by the press of a button and then seals the bottle. Although the bottle is not completely resealed, this tool helps to minimise the effects of oxidation and extends the shelf-life of an opened bottle.
Most of the more lavish (and expensive) wine gadgets that can be found on the market today, will never have a place in my home. In fact, even some of these mentioned above are unnecessary luxuries and probably only destined for avid wine drinkers and enthusiasts. If you just love to drink wine, a decent corkscrew and a clean glass is all you’ll need to make the most of your wine.
When I started writing this blog, an old adage came to mind, “there is more than one way to skin a cat”. If you believe thatthere are many different ways to achieve an objective and that the reason for drinking wine is enjoyment, then skin-fermented wines could be the means to an end.
I tasted skin-fermented white wine (henceforth referred to as orange wine) for the first time in Croatia last year and during that tasting surmised that this type of wine is not for everybody. My second experience with orange wine was last week at a wine tasting chaired by James Pietersen of Wine Cellar (Observatory, Cape Town). During this tasting I was bombarded with so many new (and sometimes weird) aromas, that I soon realised that I was out of my depth. Take a look at Table 1 at the end of this blog for more details.
After the tasting, Edo Heyns (also present at the tasting) and I discussed the wines and he reckoned that this was probably the most difficult tasting that I could have kicked off with (I started at WineLand on 1 February 2017). Edo supplied this quote, “This burgeoning niche category offers some truly delicious wines. Chenin Blanc has particularly risen to the occasion, but there are also impressive blends and Sauvignon Blancs made in this style. The tasting yielded an intriguing list of descriptors and discussions, which is part of the category’s appeal. I specifically enjoyed wines that had a neat balance of texture and acidity. Judging this style definitely tests your tolerance for funkiness. While this is part of the excitement, it could also be its Achilles heel. Skin-fermented wines should first and foremost be good wines. To me, that was not the case for some of the wines in the line-up.”
And judging by how well some of these wines are selling locally, regardless of the relatively higher price, orange wine is doing a lot of well-placed scratching. Speaking of price, these five wines ranged from R135 to R275. While a lot is said about orange wines and their sometimes obvious faults, consider that one of the browner wines at this tasting scored quite well, because of the nose and palate. As it turns out, one cannot solely judge a book by its cover (I’m on a roll with proverbs today …
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Q When and where were you born ?
“I was born in Nelspruit in 1984 which was shortly after the Grier family purchased the farm Villiera.” Then adds somewhat casually “My Dad is the great Chef and extreme adventurer and inspirational speaker, David Grier.”
Q. Where did you study ?
“I studied at the University of Stellenbosch where I graduated with a Bsc Food Science (Bio).
Q. Do you consider your approach to winemaking to be different to others ?
“Not really. I think my approach is very similar to most young winemakers way of thinking and execution, minimal intervention and let it all happen in the vineyard.”
Q. You say let it all happen in the vineyard. How involved do you get in the vineyard ?
“Well my uncle Simon is overall responsible for vineyards at Villiera but I try to get involved as much as possible as I believe the wine gets made in the vineyard.”
Q. Do you have any particular varieties you prefer to work with ?
With a wry smile “Yes, pinot noir, the heart break grape !”
Q. Have you been influenced by any particular winemaker or a wine region ?
“When I returned to South Africa I had a short stint with Kevin Grant in Elgin then I moved to be Assistant to Gerhard Smith, the winemaker at La Vierge in Hemel-en-Aarde. He taught me a lot and gave me the freedom to express myself. I worked with him for three vintages before moving to Villiera and that is a long time in my short career. ” Then adds “Of course my vintages in the USA, Australia, Tasmania and Domaine Grier in France all played their part.”
Q. What would you consider your greatest achievement as a winemaker ?
With the ever present smile. “I’m still working on it , but at this stage it has to be my Stand Alone Pinot Noir.”
Q. What “secrets” have you “developed” that make your wines different to others ?
Again with that engaging smile “I’ve got to keep that a secret otherwise it will no longer be a secret !”
Q. How important is modern winemaking equipment in your winemaking ?
“At Villiera we operate on a big scale so it plays an important role in our cellar.”
Q. You went to the University of Stellenbosch but what else have you done that is not part of winemaking ?
“My uncle and aunt (Jeff and Cathy Grier) are both Cape Wine Masters so they got me involved in the Cape Wine Academy and then I have worked as a Chef, barman, gardener and lifeguard in South Africa, Mozambique and the USA.”
Q. What of the future ?
“The future looks bright , challenging and exciting all at the same time. I am looking forward to working with the team at Villiera and can’t wait to see the results from our labours in the future and of course working with my Uncle Jeff a legend in our winemaking world.”
Written by Geena Whiting
Any athlete would agree that one cannot simply succeed on talent alone. Practise is key to becoming one of the greats. One cannot simply wake up and decide to run a marathon or swim an endurance race that same day. Your body is not the only thing that needs to be trained, mental endurance plays a major factor in achieving anything.
Recently, I had the privilege of being invited to sit on a judging panel. What a fantastic opportunity, to be able to sit with outstanding members of the wine community and taste some of the best wines our country has to offer.
Sitting there bright eyed and bushy tailed I was blissfully unaware that I had just stepped onto the starting block that would put my mental endurance and my passion to the test.
Generally a standard tasting at a wine farm is 5 wines. Where you can sit with your friends and laugh and chat. You enjoy the ambiance as the time flies by, sometimes easily spending 10 – 15 minutes tasting one wine as you are immersed in conversation and taking in the view. It is easy for 2 hours to slip by without ever glancing at the time.
Each day of tasting was spanned over about 4 hours; one would assume this is ample time for a great tasting. However this was no ordinary tasting, the wines were bought to us, twelve glasses on a tray. Each wine had to be carefully analysed: if any faults were present, for colour intensity, aroma, taste on palate, mouth feel, linearity of the flavours, the body and balance of the wine and of course the finish. For any avid wine taster this may seem standard practise, I too thought (quite naïvely so) it would be easy enough to analyse a couple of wines and then break early for lunch, but the trays just kept coming, like a turbid ocean the waves never seemed to stop.
At wine 52, I could feel myself wavering and we had already had our tea break.
“Wine 53, wine 54, wine 58… wait… did I skip a few? I haven’t written any scores since wine 53! I can’t even recall whether I rated them highly or not… Do we seriously still have 20 more to do? This is harder than I thought it would be; I can’t do this.”
Many thoughts such as these passed through my head. I felt overwhelmed as I watched how the other judges analysed wine after wine with precision and accuracy; it seemed to be easy as breathing for them.
“I cannot give up.”
I recalibrated myself, had a cracker to cleanse my palate and a glass of water to wash it down.
“Deep breath, start from number 53…”
It was imperative that I applied my mind equally to every wine, to give each wine a fair opportunity for analysis and the chance to amaze me.
Everyone has preferences: Tea vs. Coffee, Soccer vs. Rugby, Cats Vs Dogs. The same obviously applies to wine: White vs. Red, Sweet vs. Dry, Cultivar vs. Cultivar. Looking a bit deeper into wine there can even be preferences of different styles under a Cultivar, different styles such as fruit driven, oaky/spice driven, a wine trying to be true to its terroir, full bodied or light bodied. Even details down to cellar management/practises can be tasted and preferred in wines.
By wine 50, day 1, it became more difficult to judge the wines as naturally I favour a certain style over others. It was important to constantly recalibrate and give the wine credit for its specific style.
One must also be very aware of the possible terroir influences that the wine may present, i.e. is there a fault in the wine or is the wine simply representing its terroir. Is the wine degrading and showing early onset tertiary characteristics or is it displaying qualities due to poor cellar practises. All of these things needed to be constantly contemplated whilst tasting quantities of wine on such magnitude.
The more and more I taste and learn, the more I realise how little I know and the more excited I get to learn more. Aspiring sommeliers and wine makers, the only thing we can do to improve our tasting skills and our mental endurance when it comes to fully analysing wines, is to taste more wines and when I say taste, I don’t mean to simply visit more wine farms. We must sit and analyse the wines we drink over a meal, we must organize tastings with our colleges, we must become more exposed to wines not just in or immediate region but from all the wine regions this country has to offer. The only way to improve our palate and become mentally stronger is to taste and analyse more.
Each wine, like a snowflake, is unique. Quality cannot be based on preference. One must have a keen mind and a good understanding of wines and wine faults. Which is why in my opinion to judge and taste many wines of the same cultivar in that have been made with different stylistic approaches requires the mental endurance of an athlete.
By: Denise M. Gardner
The eastern U.S. growing seasons can be somewhat unpredictable. Late season rains or untimely hurricane events can be a recipe for disaster for local grape growers, and a few have been unprepared for such events in the past. These weather events can lead to higher incidences of the grey-rot form of Botrytis in addition to other rots, which may also be related to pest damage. Furthermore, these weather incidences and pest damage can ultimately impact picking decisions for growers and wineries (Osborne, 2017).
It is almost inevitable that wineries need to be prepared for end-of-season weather flops, and plan for the best possible ways to manage or maintain wine quality in light of above-average disease pressure.
One disease that winemakers can prepare for prior to harvest is Botrytis. For the purpose of this article, we’ll be using the term Botrytis to indicate the grey-mold or grey-rot form of the disease. Grey-mold, the form of Botrytismore commonly noticed in humid regions or during heavy-precipitation seasons, can ultimately affect wine quality. Peynaud (1984) has defined 4 ways in which the grey-mold can negatively affect wine quality:
- Deplete wine color (especially important in red varieties),
- Increase the risk of premature browning (through oxidative enzymes),
- Deplete varietal character (through degradation of grape skins), and
- Contribution to off-flavors developed by the mold’s presence on the fruit.
Botrytis, grey-mold, infection can force winemakers into alternative winemaking techniques in order to retain wine quality. Photo by: Denise M. Gardner
Based on a 1977 study by Loinger et al., guidelines pertaining to wine quality were developed with regards to a visual assessment of Botrytis incidence on incoming fruit:
- 5-10% Botrytis rot on clusters: noticeable reduction in wine quality; wine quality is still “good” (as opposed to very good with 0% rot on clusters)
- 20-40% Botrytis rot on clusters: marked reduction in wine quality; wine quality is “low”
- >80% Botrytis rot on clusters: wine is commercially unacceptable
With a noticeable sensory and chemical difference in Botrytis-infected clusters, it is best for wineries to develop a standard operating procedure (SOP) for assessing rot-infected fruit, as well as how the grapes should be handled and processed during production. While there is no one correct way to work with the wine, below are some suggestions or options that wineries can integrate when dealing with Botrytis-infected grapes. For a full list of possibilities, please visit: http://extension.psu.edu/food/enology/wine-production/producing-wine-with-sub-optimal-fruit/fermenting-with-botrytis-101
Some wineries will sort through all incoming grape clusters prior to the crushing/destemming process to assess for any cluster damage or presence of unwanted material. If your operation is not set up with this equipment, sorting can also take place in the vineyard. Depending on the concentration of disease and on the projected wine style or quality parameter the fruit will go towards, disease portions of clusters can be cut out in the vineyard. Or diseased fruit can be left in the vineyard to deal with after the harvest is complete. Sorting out diseased fruit from that of decent quality will reduce the impact of the mold on the wine’s aroma, flavor, and quality.
Limit Contact Time with Skins
Depending on the resource, there are various recommendations for how to handle diseased fruit. In whites, some recommend whole cluster pressing and tossing the first 10+ gallons, which are rich in Botrytis metabolites (Fugelsang and Edwards, 2007). Many recommend separating juice press fractions for white and rosé wines, as this will give the vintner more control over the chemical constituents (e.g., phenolics, enzymes, and disease-related off-flavors) in the final wine.
Depending on the desired outcome for a red wine, treating or limiting skin contact with diseased fruit may be ideal post -primary fermentation. This would include avoiding extended maceration processes. Due to the fact that the presence of Botrytis on red varieties reduces anthocyanin and phenolic extraction (Razungles, 2010) in addition to the varietal aromatics, excessive skin contact may not be ideal during primary fermentation. Whole berry fermentations, as opposed to a more aggressive crush and destem process, may help minimize extraction of Botrytis metabolites, which can also contribute to mouthfeel variations or off-flavors.
Tannin additions pre-fermentation may also be good considerations to compensate for phenolic losses associated with Botrytis infection. Pre-fermentation and post-fermentation additions may help rebuild the wine’s structure or provide constituents for color stabilization.
Flash pasteurization (i.e., flash détente) has been previously recommended for Botrysized fruit to inactive the laccase enzyme associated with Botrytis, enhance color stability in reds, as well as improve the aromatics and flavors associated with the final wine. Wines that undergo a thermovinification step tend to extract more anthocyanins and phenolics compared to traditionally fermented wines (Razungles, 2010). Additionally, this heat step helps to inactivate laccase, which can contribute to early browning or oxidation of young wines. However, commercial producers may not find this technological application easily accessible.
Therefore, in addition to minimizing skin contact time, winemakers will want to reduce contact time with the gross lees, and may also remove the wine from fine lees associated with the mold-infected fruit quickly. The integration and use of clean, fresh lees, however, is still encouraged. Removing the lees associated with mold-infected fruit can help reduce additional contact time with rot metabolites that have settled out with the lees. This inhibits further integration of those metabolites into the wine.
Inoculate with a Commercial Yeast Strain
The presence of rot is one incidence in which processing techniques (e.g., cold soak) that encourage native microflora to dominate the fermentation are probably not desired. Things like cold soak and native ferments allow ample opportunity for the mold to progress and contribute to the wine’s flavor.
Fruit that has rot or microflora issues is best inoculated with commercial yeast and malolactic bacteria strains to outcompete the native microflora (including those microorganisms that contribute to the rot), and to give the fermentation its best chance at completing the fermentation cleanly. Remember that proper yeast nutrition is important to support the yeasts’ growth and to reduce the risk of hydrogen sulfide development. For more information on determining the starting nitrogen concentrations (YAN) and how to properly treat your fermentation with added nutrients, please refer to:
Penn State Extension’s Wine Made Easy Fact Sheet: Nutrient Management During Fermentation
With high Botrytis concentrations, a more robust yeast strain may be preferred in order to quickly get through primary fermentation. A quicker fermentation may simplify the aromatics associated with the wine, but it will also ensure little opportunity for additional spoilage. Saccharomyces bayanus strains are often selected as more robust yeast strains.
Use of commercial yeast strains can be a valuable tool when dealing with disease-infected fruit. Photo by: Denise M. Gardner
Use of Sulfur Dioxide
Sulfur dioxide additions at crush will be determined based on the style of wine in which you are producing (e.g., white, rosé, red, etc.), but in general, the use of sulfur dioxide can help inhibit further spoilage of your product and retain antioxidant capacity. Sulfur dioxide additions in the juice stage will help minimize early browning, but primarily inactivate PPO.
In general, botrysized wines tend to require more sulfur dioxide as Botrytismetabolites bind with free sulfur dioxide (Goode, 2014). This is true even when processing wines with the noble rot version of Botrytis.
When primary fermentation, and malolactic fermentation (dependent on style), is complete it is a good idea to ensure that the wine has an adequate free sulfur dioxide content in order to retain its antimicrobial protection.
Some fining agents may also be applicable in the juice stage. For example, some producers find it helpful to fine juice with bentonite in order to reduce protein content, as well as help minimize rot-associated off-flavors or partially reduce laccase concentrations.
PVPP can be added to the juice to reduce potential browning pigments or their precursor forms (Van de Water, 1985).
In both of these scenarios, neither bentonite or PVPP is specific for rot-related constituents, but each could be helpful to avoid potential challenges later on in the production process.
The presence of Botrytis can also contribute glucans to the must/wine, which can cause filterability problems for heavily-infected wines. In this situation, many suppliers have beta-glucanase enzymes that can be applied either to the juice, wine, or both, to help breakdown the glucans and enhance ease of filterability.
A Word about Laccase
Both polyphenol oxidase (PPO) and laccase can cause early browning in grapes and wine. However, PPO is inhibited by the alcohol content that is developed during primary fermentation. Laccase, however, is not inhibited by the presence of alcohol, and can only be inactivated by a pasteurization step, heated to at least 60°C (140°F) (Wilker, 2010).
Grapes tend to be higher in laccase concentration when infected with Botrytis, and, thus, wines produced from grapes that had a high incidence rate of Botrytis can develop a brown hue post-primary fermentation. This oxidative activity can occur even in young wines.
If you are concerned about the prevalence of laccase in diseased-fruit, wineries can submit wine samples to a wine lab for a laccase test. Or, if you own a copy of “Monitoring the Winemaking Process from Grapes to Wine: Techniques and Concepts” by Patrick Iland et al., pg. 90 and 94 have 2 laccase test protocols that outline how wineries can assess oxidation by laccase. The results of these test will indicate if extreme treatments are required during production to avoid the rapid and early oxidation caused by laccase.
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Wilker, K.L. 2010. How should I treat a must from white grapes containing laccase? In Winemaking Problems Solved. CRC Press: Boca Raton, Florida. 398 pg.