So you want to join our community!

If you already have an account, all you have to do is

Use and continue

New World Wine Maker Blog

Botrytis Bunch Rot: Winemaking Implications and Considerations

By Dr. Molly Kelly, Enology Extension Educator, Department of Food Science

In a previous post, Bryan Hed discussed early fruit zone leaf removal and its effects on the development of Botrytis bunch rot and sour rot. This is a good time to review the implications of molds and fruit rots on wine composition and quality. I will also discuss remedial actions in the winery.

Screenshot 2018-06-01 08.49.50
Here we will focus on the most common bunch rot pathogen of mature berries, Botrytis cinerea. How severe can Botrytis bunch rot be before wine quality is impacted? This will depend on the type of rot as well as winemaking techniques however, even low levels of infection have been shown to negatively impact wine quality. Red wine quality was shown to be affected by as low as a 5% infection rate of B. cinerea. Extended skin contact in red winemaking can increase the effect of bunch rots on the finished wine.  While B. cinerea can be linked with sour rot, it is more commonly associated with other fungi including Aspergillus spp. Sour rot is caused by yeast, acetic acid and other bacterial growth. When acetic acid bacteria, yeast and filamentous fungi are present together, high levels of acetic acid can result. Berries infected with sour rot have a distinct vinegar smell that may be combined with the presence of ethyl acetate. Ethyl acetate is an ester described as smelling like nail polish remover.

Laccases are enzymes produced by fungi. They break down anthocyanins and proanthocyanidins which are important phenolic compounds that contribute to palate structure and wine color. In white wines, some aromatic compounds can be oxidized resulting in the production of earthy aromas.

The largest change in must chemistry as a result of Botrytis growth is seen in amounts of sugars and organic acids. Up to 70 to 90% of tartaric and 50-70% of malic acid can be metabolized by the mold. Resulting changes in the tartaric:malic ratio cause titratable acidity to decrease and pH to increase.

There may also be clarification issues as a result of infection. The fungi produce polysaccharides including β1-3 and β1-6 glucans as well as pectins as a result of the production of enzymes capable of degrading the cell wall. In the presence of alcohol, pectins and glucans aggregate causing filtration difficulties. To mitigate this issue, pectinolytic and glucanase enzymes can be used. When adding enzymes allow at least six hours prior to bentonite additions.

Botrytis cinerea strains differ in the amount of laccase produced. This enzyme can lead to oxidation of aroma/flavor compounds and browning reactions. It can be resistant to sulfur dioxide and not easily removed with fining agents. Bentonite may remove enough laccase to minimize oxidative problems. For varieties where the potential for oxidation is increased, ascorbic acid additions can be added to juice. Since Botrytis uses ammonia nitrogen there is less available for yeast metabolism. Vitamins B1 and B6 are also depleted. Therefore supplementation with nitrogen and a complex nutrient is required. Yeast assimilable nitrogen (YAN) should be measured and adjusted accordingly to avoid stuck fermentations and production of hydrogen sulfide. Also consider inoculating with low nitrogen-dependent yeast and use more than the standard amount of 2 lbs. /1000 gallons.

Wine off-flavors and aromas result from a number of compounds when made from grapes with Botrytis(and other bunch rot organisms). Descriptors include mushroom and earthy odors from compounds such as 1-octen-3-one, 2-heptanol and geosmin. Since fruitiness can be decreased, the use of mutés (unfermented juice) from clean fruit can be added to the base wine to improve aroma. Botrytis also secretes esterases that may hydrolyze fermentation esters. Monoterpenes found in varieties such as Muscat, Riesling and Gewürztraminer can also be diminished.

When Botrytis infection is present, consider the following processing practices in addition to those mentioned above.

  1. Remove as much rot as possible in the field and sort fruit once it arrives at the winery. Using sorting tables is a great way to improve overall wine quality.
  2. Whole-cluster press whites, using very light pressure, and discard the initial juice.
  3. Harvest fruit cool and process quickly. Sulfur dioxide can be added to harvest bins to inhibit acetic acid bacteria.
  4. Enological tannin additions will bind rot-produced enzymes. They can also bind with protein and decrease the bentonite needed to achieve protein stability. Note: Remember to not add tannins and commercial enzymes at the same time since tannins are known enzyme inhibitors. After an enzyme addition allow six to eight hours before adding tannins.
  5. Minimize oxygen uptake since laccase activity is inhibited in the absence of oxygen. Inert gas can be used at press, during transfers and to gas headspace.
  6. Use a commercial yeast strain that will initiate a rapid fermentation. The resulting carbon dioxide will help to protect against oxidation.
  7. Once fermentation is complete, rack right away. Both Botrytis and laccase settle in the lees.
  8. Phenolic compounds are the main substrate for fungal enzyme activity. Removal of undesirable phenolic compounds can be achieved using protein fining agents (ex: gelatin, casein, isinglass). The synthetic polymer PVPP can also be used in juice or wine to remove oxidized phenolic compounds.
  9. Only cold soak clean fruit. Avoid cold soak and extended maceration on Botrytisinfected fruit as this may encourage fungal and bacterial growth.

As always, it is best to avoid rot-compromised fruit, however, using these practical winemaking tips should help to minimize negative impacts on wine production and quality.

References

DeMarsay, A. Managing Summer Bunch Rots on Wine Grapes, Maryland Cooperative Extension.http://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/viticulture/ManagingSummerBunchRots.pdf. Accessed 7 May 2018.

Ribereau-Gayon, P. 1988. Botrytis: Advantages and Disadvantages for Producing Quality Wines. Proceedings of the Second International Cool Climate Viticulture and Oenology Symposium. Auckland, New Zealand, pp. 319-323.

Steel, C., J. Blackman, and L. Schmidtke. 2013. Grapevine Bunch Rots: Impacts on Wine CompositionQuality, and Potential Procedures for the Removal of Wine Faults. J. Agric. Food Chem. 61: 5189-5206.

Zoecklein, B. 2014. Fruit Rot in the Mid-Atlantic Region, On-line Winemaking Certificate Program, Wine Enology Grape Chemistry Group, Virginia Tech. http://www.vtwines.info/. Accessed 16 April 2018.

Zoecklein, B. 2014. Grape Maturity, On-line Winemaking Certificate Program, Wine Enology Grape Chemistry Group, Virginia Tech.http://www.vtwines.info/. Accessed 16 April 2018.

Read article

Let’s give it up for the wine bars, baby

Any wine lover, wine maker and wine connoisseur worth their weight can tell you one of the largest problems with the South African wine industry is the total lack of local market interest. The current South African wine drinkers are predominately rugby moms who drink iced Chardonnay and while watching Jan play his Saturday morning match against Paarl or tragically basic, young teeny boppers who drink “rosé all day”. The rest of the population sticks to “branners and coke”, beer or ciders.

As a student I have found myself confined to the four Bs – Bartinney, Bramptons, Balboa and Bohos. Now the first three are what we need in South Africa if we want to encourage a new generation of informed, interested and adventurous wine drinkers. The latter – not so much. Robertson box wine  may be a successful product but I am a firm believer that wine should not be drunk from a juice carton and served with a beer glass of ice.

As it is, the only time the average student is exposed to a “Savvy B” instead of a “Sauvignon Plonk” is if they’ve ventured out to the surrounding wine farms, usually only for the pre-dance fashionable photos, because no one can afford the übers fees for a weekly wine tour. Luckily for wine students this occurs more often due to enthusiasm from all your class mates to go for a sneaky tasting after every minor accomplishment. Yay! We finished a prac report let’s go wine tasting. Yay! We attended all out classes today let’s go wine tasting.

Ironically, Stellenbosch as the wine capital of South Africa has a serious deficiency of wine-drinking platforms for students, particularly those who don’t confine their drinking times to 10am until 5pm as most wine farms do. University is the place of innovations, where trends are born and die and sadly, the trend of wine drinking starts and stops at “Tassies” and “Four cousins”, not to say these aren’t well-respected wines in their own right, but let’s be honest, any wine snob would be horrified to find themselves with a glass of tassies while unwinding after a horrible test.

I have been fortunate enough to travel many places within and outside of South Africa. The wine lists littered across the rest of South Africa are depressing and it’s no small wonder that wine is not the hot accessory we need it to be. In international metropolitan areas, like Barcelona and London wine is the answer to everything. Hot new wine bars open up more often than a cellar intern stress-cries during harvest (which in my case was at least once a day).  And this is where South Africa is seriously lagging behind. With so much to offer to the new untapped hipster, trend-setter consumers we seriously fall short.

Part of South African wine charm is the diversity (if you like clichés we could say rainbow nation of wine). We have historic Constantia wines to the reputable Stellenbosch powerhouses and now we also enjoy the yuppie, alternative Swartland surprises.

Wine is seen as snobbish and elusive by the majority of the population. But, that is something so easy to change. Bring out the screw caps, crown caps and orange wines to the young population. We’re all equally lost, alone and confused when it comes to the apricot-bomb Viogniers or orange Semillon. It’s the great equaliser that we’ve been waiting for and together students can become the pioneers in the alternative wine movement.  Once wine can be viewed as trendy and hip then the young adults will flood the market and perhaps we will have a local wine consumption to be proud of.

So why is it so difficult to get these wines to break into the new market of the young trend setters, ubiquitous across campuses? Why are there no wine bars populating every nook and cranny of South Africa’s CBDs? Bring on the hipster wine bars where Malbec comes in a mason jar and we get deconstructed Pinotage tastings.  Every youth with their  vintage clothing, vinyl records and “Rocking the Daisies” wristbands from 2017, 2016 and 2015 will show up to experience the alternative and innovative wines on offer.

Read article

Making invisible things visible: Do yeast cells stick to cork during bottle aging?

Yeast do not seem to form biofilms on the bottoms of corks when they’re used, rather than metal crown caps, to secure Champagne bottles during their in-bottle secondary fermentation. This, at least, is the conclusion of an article in the current issue of the American Journal of Enology and Viticulture (paywall), in which Burgundy-based authors investigated the question for the sake of understanding whether Champagne producers, some of whom are using cork for their longer-aging wines, risked upsetting in-bottle fermentation dynamics. After a year of bottle fermentation and aging, a few cells apparently got caught in porous crevices of the cork, but systematic growth presaging the tenacity of a biofilm wasn’t happening.

That finding will no doubt interest the odd sparkling wine producer. Much more interesting is the method they used to make “invisible” cells visible and so reach that conclusion.

How do you determine whether a microbial biofilm is growing somewhere?

Before it reaches scrape-it-off-with-a-fingernail thickness, the answer is usually microscopy. But what kind of microscopy? Let’s say you want to see the very earliest stages of what might become a biofilm. You want to visualize individual yeast cells sticking to a rough, craggy surface with lots of crevices for hiding—the cork. Pointing a light microscope at the cork won’t do. The kind that you probably used in school to see cells suspended in liquid (from your cheek, or bacteria from your teeth), and that many small wine and brewery labs use to check for live cells requires that whatever you’re looking at be thin enough for light to pass through. Slicing corks into sections thin enough for light microscopy might destroy or displace any would-be-biofilm-forming yeast cells. Moreover, can you imagine scanning the bottom of cork after cork, continually asking yourself: is that a yeast cell, or a bit of cork shaped like a yeast cell? A digital image analysis program trained to recognize yeast cells might address the latter problem (with some degree of error), but the whole task clearly calls for a more sophisticated technique.

When your sample isn’t transparent enough for light microscopy, fluorescence microscopy can be an alternative; instead of visualizing light passing through the sample, fluorescence microscopy relies on whateveritis you’re examining absorbing and then emitting light—fluorescing—which can then be picked up by the microscope’s detector.* Conveniently, cork and other plant matter comes with a built-in fluorescent molecule; lignin, a rigid polymer and major contributor to the stiffness of wood and bark, is easy to see under the microscope …

>> CLICK HERE TO READ THE FULL ARTICLE

Read article

The Hard-Working Hands of Harvest

“Meisietjie, Lena is die Wingerd-Aaantie (aunty)”, this was one of the very first sentences I heard when I started my internship this year (2018). While I sit here, taking a hefty sip of chilled Sauvignon blanc, I can’t help but think about all of the unseen and almost unheard of hard work that has been poured into each lingering sip of wine.

Some of my fellow cellar-dwellers have been working in the industry for longer than I have been alive; it very quickly dawned on me that these men and women are fountains of knowledge and quirky stories. A winemaker is only as good as the team supporting them, this is a very important lesson for any young or aspiring winemaker to learn. As far as my winemaking internship goes, I can wholeheartedly say that I have landed with my bum in the butter. In my very first week, I had already been taught (by the cellar team) how to build lines, operate pumps, pressure-rack barrels, set up acid and alcohol trials etc..

Almost two months down the line, I can very clearly see why my colleagues are so eager to get to work in the mornings. Each time the viticulturalist brings in grape samples from the vineyard, one of the cellar workers rushes to find me and tell me that I must come and do ripeness asssesments. Within the same breath, forgetting that I have not yet taken any sugar readings, I either get asked, “Where is the sugar lying? Wanneer gaan ons pars (when are we going to harvest)?” or promptly told, “No, no, they are not ready yet”. I couldn’t help but feel a little envious of the winemakers, to have a team that is this enthusiastic and motivated to start harvesting.

In the vineyard, I am constantly greeted with smiles, and even though I don’t yet know the entire team’s names, they all know my name. Every opportunity I have to work in the vineyard is met with people enthusiastically asking me to work with them, as they show me the do’s and don’ts of the day’s vineyard tasks. I think, as consumers, it is very easy to give the winemakers all of the credit when we taste a phenomenal wine, and it’s equally as easy to forget that no person can make a great wine on their own. It’s definitely a team effort.

As much as the teams are teaching me, I have found that learning and teaching work both ways. While doing some crop dropping (green bunches were removed) in order to allow for the Merlot bunches undergoing veraison to ripen, one of the team members said she could taste something familiar in the berry but couldn’t quite put her finger on it. I was very quick to pop a berry in my mouth, purely out of curiosity, and rapidly replied with, “it’s minty, and tastes a bit like bell-peppers”. Her face lit up as she recognised these flavours and agreed with me, where after she explained to me that it made a lot of sense as the viticulturalists wanted us to do the crop-dropping in order to try and lessen the green characteristics of the berries.

I would like to take my hat off to all of the men and women behind wine and thank them for the countless hours of hard work they have put into each vintage. From working long days in 30-40°C weather, to working 15+ hour shifts during the harvest season, I have not heard a single complaint. I am constantly surprised by the amount of passion and hard work the teams put into every task they’re given and how readily they offer help to anyone who struggles. They hold each other accountable for their work, truly working as a team by making sure everyone is doing their work properly.

When harvest started, I didn’t expect anyone to remember me after my pruning practical on the farm in June, however very few had forgotten. While walking through the vineyards on a very hot day, hanging up containers with biological control agents (parasitic wasp eggs), I bumped into one of the suckering  teams. I was immediately recognised and greeted with a smile, while being called over to come and see what the team was doing. I was feeling exhausted, and quite honestly did not want to walk all the way back to the other side of the row I had just hung the control agents in. I somehow mustered up enough motivation to put one foot in front of the other and make the journey. What should have been a quick “hi-and-bye” turned into a 45-minute chat about everything from insects, to love advice and weekend shenanigans. I learned another important lesson that day, sometimes, all someone needs is a smile and a good story or two to motivate them and give them a little bit of encouragement. After talking to some of the team members, I had forgotten all about my exhaustion and immediately felt more energized.

Remembering something a viticulturalist had once said to me about the workers always being loud and chatty in the vineyards, I finally understood why. When you’re enjoying your work and the company, laughing and singing while you get through the day, you begin to look forward to tomorrow. Hard work is made a lot easier when it’s appreciated. So, here’s a big THANK YOU, to all of the winemakers, cellar workers, viticulturalists and vineyard workers for all of the hard work that goes into each divine sip of wine!

Read article

Sensory evaluation of mouthfeel in wine

by Renée Crous, Valeria Panzeri & Hélène Nieuwoudt

Sensory panels often avoid the evaluation of mouthfeel sensations in wine, since it implies (for many non-wine experts) complex, and abstract concepts. However, mouthfeel is an important dimension of wine quality, and it is, therefore, necessary that these properties are also included in routinely sensory tests. In our recently completed Winetech funded research project IWBT W13/02, “Rapid descriptive sensory methods for wine evaluation – special focus on further optimisation of rapid methods and streamlining of workflow”, we have developed two useful protocols for the assessment of mouthfeel in wine that can be used by sensory panels in the industry and research. This article describes the protocol that is based on the classic descriptive analysis (DA) method. In line with the objectives of project IWBT W13/02, we also optimised a rapid sensory method, polarised sensory positioning (PSP) to evaluate mouthfeel in wine. The rapid method does not require a trained DA panel and can be completed in shorter sessions. The protocol for the rapid method is discussed in a subsequent article.

What is meant by mouthfeel?

Mouthfeel refers to the sensory perceptions experienced in the mouth when a wine is consumed. Wine judges often describe wine as “full and round with good concentration, and length”, thereby implying that the product has good mouthfeel properties. While these phrases are commonly used in the popular media, people differ in their understanding of what exactly is meant by them. In scientific publications, several terms are grouped under so-called in-mouth sensations; these include fullness, heat, complexity, balance, length and mouthfeel.

Evaluation of mouthfeel by sensory panels

It is a challenging task to train a sensory panel to evaluate wine mouthfeel sensations. DA is one of our most accurate sensory test methods and provides two important outputs. Firstly, all the sensory properties that are perceived in a set of wines are identified and named by a panel of trained tasters. Secondly, panellists also score the intensity of each property on a line scale (ranging from 0 to 100, for example).

Physical standards are used to train a panel for the first task (identification of sensory properties). For example, a fresh lemon can serve as a standard for the lemon character in wine aroma. It is clear that all the panellists must have agreement on the sensations of the lemon character, as well as the particular word that describes the specific character, before the panel can proceed to assess the wines. With abstract concepts, such as length, complexity, and balance, there are no so-called physical standards, and an alternative plan must be made during training of the panel.

Another major challenge is to calibrate panellists to rate the intensities of the mouthfeel sensations on a line scale. It speaks for itself that the line scale must be used consistently by different panellists and on independent sets of wines; otherwise, comparative studies are not possible.

To illustrate these challenges: in this Winetech project, we wanted to evaluate the mouthfeel sensations of old-vine Chenin blanc wines (produced from vines 40 years and older) with the DA method. It is well known among wine experts that the old-vine Chenins have much more complex mouthfeel properties, compared to some younger vine Chenins. For panellists to use the line scale consistently to showcase these differences, they need to have in-depth experience and knowledge of the entire product category. This is seldom the case. Also in dealing with this challenge, adjustments had to be made to the standard DA protocol …

>> CLICK HERE TO READ THE FULL ARTICLE

 

Read article

MEET RUDGER VAN WYK – WINEMAKER AT STARKE-CONDE WINES

Q. When and where were  you born ? 

“ I was born in 1991 in George in the Southern Cape. Not quite in winemaking territory.”

Q. Where did you study and what qualification have you got ? 

“I studied at the University of Stellenbosch where I achieved a BSc Viticulture and Oenology degree.”

Q. Do you consider your winemaking approach to winemaking to be different to others ?

“No. I use what I was taught and have learned since then in various cellars. All well tried   good winemaking practices.”

Q. How involved do you get in the Vineyard ? 

“I try to spend as much time as I possibly can in amongst the vines as that is where a great wine begins. “

Q. Do you have any varieties you prefer to work with ? 

“I have cabernet sauvignon at top of my list but Sauvignon blanc and Chenin blanc are about tie for top with cabernet. However I find all our varieties  a joy to work with , because  each varietal is unique in it’s own way.”

Q. Have you been influenced by any particular winemaker or wine region ? 

“Abrie Beeselaar and Jose Conde , with their out of the box thinking have been a great influence. I found my visit to Burgundy to be a region  so very inspiring just to see the passion and love they have for their wine.”

Q. What would you consider your greatest achievement as a winemaker ?

“Inspiring others to follow their passion and work hard in what they love. We as winemakers will always  be in search of making the perfect wine, so when the day arrives (if it arrives) I will re-answer the question !”

Q. What “secrets”  have you “developed “  that make your wines different  to others ?

“No secrets  but follow your gut and always be in sync with Mother Nature.”

Q. How important  is modern winemaking  equipment  in your winemaking ?

I’ll  try to utilise it as a tool in the winemaking process to enhance the quality that nature gives us, but I strongly believe in the grape doing it’s natural thing.”

Q. What has been your history to get you to where you are ?

“I started my first harvest at Uitkyk wine estate, as an intern during  my final year of studies at University of Stellenbosch. The year after  I became a Capewinemaker Protégé, where I started at Kanonkop, under the guidance of Abre Beeselaar. I moved to Ntida wine estate in my second year, to learn more about cool climate winemaking.  In that year I was lucky  to do a harvest in Burgundy, where I finally fell in love with wine  and where that passion still drives me to this day. With all this experience I was taken on by Starke Conde where I have been given the opportunity to put it all into practice.  I sincerely believe that life set me up to get to where I am and to be working with the varieties I love.”

Read article