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New World Wine Maker Blog - yeast

The (Colloidal) Matrix part I

Morpheus:Unfortunately, no one can be told what the Matrix is. You have to see it for yourself. ”

For particularly the higher price point wine market segments, wine maturation is a very significant step. Some factors to consider are: the tank or barrel size, the use of oak or not, the length of maturing and ageing conditions and to micro-oxygenate or not. Wine transfers and managing “wine lees” is one of the most important dimensions of enhancing “wine quality through mastering wine maturation”.

What is “wine lees?” I guess it depends on who you are talking to… The official definition of  lees is the “residue that forms at the bottom of recipients containing wine, after fermentation during storage or after authorized treatments, as well as the residue obtained following the filtration or centrifugation of this product” (if you are ever inclined to read the EU Regulations)…

I suppose lees for me as a winemaker, is a tool to potentially reach a stylistic goal, i.e. to enhance the structure and mouth feel of the wine, to enhance body and increase the aromatic complexity, and ultimately to achieve longevity.

There are a few technicalities to consider whenever lees is discussed.  Heavy lees in red wines is considered to be a combination of yeast cells, tartrate crystals and precipitated color matter and tannins; or involve compounds made up of proteins, tannins and polysaccharides. In white or rosé wines heavy lees may consist of solid grape particles (depending on the clarity of the juice prior to primary fermentation), yeast cells, tartrate crystals and precipitated colloidal matter. It may even include residues of settling treatments such as PVPP, bentonite and casein.

The technical definition of light lees (or “functional lees” as I call it) is: “particles which remain suspended 24 hours after a wine has been moved, and consist mainly of yeast cells and lactic acid bacteria.”

The truth is that, no matter the semantics, optimal lees management will contribute to quality in one or more of the following ways:

1. Increased polysaccharides benefits

-A direct sensorial effect on wine structure – roundness, volume and coating. (Polysaccharides, of different origins, are added to numerous products such as sweets and dairy desserts, in the food industry.)

-Some released colloids or mannoproteins block the reactions of tartrate crystallization and thus enhance tartrate stability.

-Enhanced protein stability

-Binding reactions between tannins, color pigments, proteins and volatile compounds stabilize some of these compounds, which “protects” them against polymerization and precipitation.

-Mannoproteins may have an indirect effect on astringency when they combine with phenolic compounds from grapes or oak, thus acting as protective colloids that decrease the intensity of tannin.

2. Amino acids and nucleic acids are released. The cell content of yeast is rich in amino acids and nucleic acids and is regarded in the food industry as flavor enhancers. This may intensify various taste sensations and complex aromas according to Delteil, as the concentrations of these compounds can be affected by lees contact.

3. Esters & other volatiles are released, especially the esters of fatty acids with sweet and spicy aromas. Primary grape aromas are complemented by the sweeter and spicy aromas of the ethyl esters.

Many wines from around the world and even dimensions of marketing are built upon this simple term – “sur lie.” From wonderful, rich Muscadets from the Loire, great Burgundies, to two of South Africa’s greatest unwooded Chardonnays and Chenins – the Jordan Chardonnay “Sur lie and the Bosman Family Vineyards Chenin blanc “Sur lie.

 Look out for The (Colloidal) Matrix Part II

Bertus Fourie is a winemaker, turned Enology lecturer and creator of the Barista coffee Pinotage.

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Are your yeasts on sterols?

Recent crackdowns on doping in sport have made all of us more aware of the effects of performance enhancing supplements. This got me thinking. What if winemakers could come up with a legal magic potion for yeast? Like the magic potion that enabled Asterix and Obelix to defeat the Romans time after time. Something that would give mere mortal yeasts super human (rather super yeast) qualities?

An increasing worldwide trend is longer “hang-time”. Delaying harvest might increase berry aroma and decrease acidity, but it creates a unique problem for our little athletes. Increased sugar leads to increased alcohol levels in wine made with these grapes. Fermenting yeast thus run the risk of being smothered in the alcohol they produce as a result of them snacking on sugar. Fortuitously, there is a magic potion that you can give your yeast to boost their viability during fermentation.

First, let’s look at the definition of sterols: “Any of various alcohols having the structure of a steroid, usually with a hydroxyl group (OH) attached to the third carbon atom. Sterols are found in the tissues of animals, plants, fungi, and yeasts and include cholesterol and ergosterol.” Here comes the interesting part. Sterols and unsaturated fatty acids (UFA’s) are survival factors during fermentation, but oxygen is needed for the synthesis of said survival factors. With insufficient amounts, the yeast cell membrane functions poorly, especially during highly anaerobic conditions and especially with increasing ethanol levels. Inadequate sterol concentrations around flux controlling proteins in the yeast cell membrane cause damage to the cell membrane and ultimately results in cell death (read: stuck or sluggish ferment!). The key role between oxygen and sterols now becomes evident. Simply put, controlled and timely oxygen addition = more sterol synthesis = better ethanol resistance = happy yeast = happy winemaker.

In my previous life, I’ve found it useful to add oxygen to red ferments anytime from a third of the way through alcoholic fermentation, up to halfway. This roughly corresponds with the end of the cell growth phase and research has shown that an oxygen addition of five to ten mg/L has a very positive effect on cell viability. Another trick is to combine oxygenation and nutrient addition with a pump-over or punchdown. Complex yeast nutrients contain inactivated yeast, which is a good source of sterols. The abovementioned trick also counteracts reductivity, which every winemaker deals with at some stage.

Research is ongoing to gain more insights into how yeast sterol uptake and synthesis affects cell viability. Ergosterol is one of the main compounds being studied, but I’ve also read a paper which outlines the addition of cholesterol to a fermentation! Fermenting yeast are just as happy with cholesterol as they are with ergosterol, but I seriously doubt if winemakers will be chucking cholesterol by the bucketful into their wholesome red wines!

Bernard Mocke is a technical consultant for Oenobrands.

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Winemaking in the Twilight Zone

You’re traveling through another dimension, a dimension not only of sight and sound but of mind; a journey into a wondrous land whose boundaries are that of imagination. That’s the signpost up ahead — your next stop, the Twilight Zone.

—Rod Serling

As a child, my favourite show was “The Twilight Zone”. It was an imaginative place, filled with uncertainty, adventure, terror and discovery. While these elements will keep any youngster nailed to his seat, a winemaker should tread lightly when entering “The Twilight Zone”.

Wine yeast companies usually offer broad ranges of yeast and bacteria, with bio-converters for every wine style or grape variety imaginable. There is a downside to this myriad of yeasts… Winemakers sometimes avoid browsing through pages of technical hoopla, allowing themselves instead to be guided through the fermentation process and beyond by some vague, intuitive notion. I am all for adventure and discovery, but tend to shy away from uncertainty and terror. Be that as it may, some winemakers wittingly step into “The Twilight Zone”. Here are some examples of lesser known (and sometimes risky) fermentation techniques.

Yeast rehydration is a critical process that paves the way for a successful ferment. However, I know a winemaker who never does this for his barrel fermented Chardonnay. He simply adds the powdered yeast to the must by pouring it directly into the bunghole. His rationale behind this is a very steady and gentle onset of fermentation! Might I add that I rate his Chardonnay as one of the best I’ve tasted. I know another winemaker who adds un-rehydrated dry yeast to his freshly crushed grapes. He said that the action of the pump does a good job of dispersing the microbes into the must. I’ve also heard of a winemaker who rehydrates his yeast in warm must (how would one heat up a bucket of must?) and guess what? According to him he has not experienced problems until this year! Yeah, if you believe that…

In the olden days (realise that the past forms an integral part of “The Twilight Zone”), winemakers lacked the technology that we have today. Cooling down fermenting must during 1930 to 1950 presented a major challenge. One questionable technique included running must in the channels and gutters between tanks and blowing air over it with a fan, before pumping it back into a fermentation tank.

Finally, as a farewell to our foray into “The Twilight Zone” of fermentation, I once did a tour of a private cellar in Germany. The winemaker, in a desperate attempt to get his stuck tanks to start fermenting, scraped the mouldy walls and inoculated the tanks with the centuries old yeasts and fungi. The resulting wine tasted like a horse had a bath in it. Scary isn’t it?

Bernard Mocke is a Technical Consultant for Anchor Wine Yeast.

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Some advice on natural fermentations

It’s the time of year after the southern hemisphere harvest when the unfortunate with stuck fermentations seek advice. There are various causes of stuck fermentations with “natural” fermentations being one of the more common ones. Working for a commercial wine yeast producer I am often viewed as not being supportive of this practice. This is not entirely true. I have tasted some exquisite wines produced via spontaneous fermentations. The times that I am critical of the practice it is merely because I am familiar with the risks involved with it. At the end of each harvest I have to help various winemakers to re-inoculate their stuck “naturally fermented” wines with commercial yeast. So over time I have come up with a few guidelines as to how to somewhat make your natural ferments more “secure.” Unfortunately success can never be guaranteed.

Karien’s advice on more secure natural ferments:

1. Do not attempt natural fermentation when the initial grape sugar is above 24°Brix. This works for some people – they are the exception to the rule. Most naturally occurring wine yeasts are not very alcohol tolerant.

2. Add some complex yeast nutrients containing inorganic nitrogen (DAP) at the start of fermentation as to increase biomass formation. One of the main differences between inoculating with commercial yeast and letting nature takes it course is the size of the yeast population starting the fermentation. You need a critical mass to finish a fermentation.

3. Do not stress the yeast by fermenting at extreme fermentation temperatures, i.e. below 17°C or above 25°C. Your specific mix might not be cold tolerant or very alcohol tolerant – the higher the fermentation temperature, the higher the alcohol toxicity.

4. Add yeast cell walls to adsorb medium chain fatty acids produced by stressing yeasts, thereby making the environment less toxic.

5. If you ferment only some tanks natural and others using commercial yeasts, make sure that the commercial yeasts you use are very strong/alcohol tolerant fermenters. That way you can add that lees (once it has completed fermentation) to the natural tanks in case you develop sluggish fermentations.  

This advice is not based on my experience of conducting natural ferments, seeing that I have never done any. It is based on my technical knowledge of what yeasts can and cannot do. Use it, don’t use it. Oh, that reminds me, we once did a yeast trial in our lab (at the yeast factory) and the control – with no added yeast – fermented as fast as the experiments. Yeah….so much for that theory…

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Something is rotten in the state of Denmark…

Is Brett a bad thing? Mmmm….How long is a piece of string? But as a winemaker you should probably have a decent, well informed opinion about Brettanomyces and what it does in wine. I remember as a student going to classes at the Cape Wine Academy in South Africa. We always decided to sit right in the back of the class, because we believed our vocabulary, especially with regards to adjectives, were not sufficient enough to explain why we loved or hated a wine. (And apart from that, we felt quite intimidated by the glares of our fellow classmates should we not agree with some of them…). Luckily I soon realised that it is okay to have a different opinion, because as for the perception of tannin, consumers differ widely in their sensitivity to aromatic substances. Hence, the reason why people differ in opinion when it comes to their perception of a wine and its quality is because of their genetics and not their vocabulary.

Anyway – we’re on Brett. What is it? Apparently also a “probiotic culture”, which will probably make Nicolas Joly shrivel with anguish. I tasted a very highly recommended fruit infused tea the other day. It smelled like the cow shed (the typical old, wet ones) where I learned how to milk cows when I was little. I reflexively read the back label. It contained five different probiotic cultures of which Dekkera anomalaus was one. And I am sure you probably know this, but Dekkera is the anamorph of Brettanomyces. This would be an example of Brett gone badly. Way too much of the pencil shaving, spicy, wet cow yard, funny farmyard, funky, damp hamster cage nuances that can be absorbed and smiled upon by this wine addict.

Five species of Brett are associated with wine, of which B. Bruxellensis is most common. The reason for growth in wine mediums include poor SO2 management (and molecular SO2 influenced directly negatively by a high pH), riper grapes and residual sugars. Too high nitrogen levels in musts (mostly as a function of winemakers who do not regard nitrogen management important) also fuels the action of Brett. What does the spoiled wine taste and smell like? Well, it depends on the aromatic culprit. Three common molecules are responsible for much frustration – 4-ethyl phenol (smells like horse stables, sweatiness, cow yard/barnyard, burnt beans) is the main culprit, IVA or 3-methylbutiric acid (smells rancid, horsy) which is a volatile fatty acid and last, but not least, 4-ethylguiacol (smoky, spicy aromas).

And then, the million dollar question: Can it add to complexity in a wine? I believe yes, particularly if the spicy, smoky 4-EP is present. There is however, opposing opinions amongst scientists and winemakers. Some icon wines have been associated with Bretty nuances. Beaucastel, Henschke, Jaboulet’s La Chapelle and even Penfold’s Grange come to mind and interestingly enough, it is postulated that cultivars such as Shiraz and Mourvedre have more phenolic precursors, thus making it more likely to show Bretty characteristics.

I guess in the end, you should probably ask yourself what you get from Brett, how much of it and how, and whether it contribute to the wine’s typicity and quality.

And ultimately measure your sales, just to make sure you got it right…

Bertus Fourie is a winemaker, turned Enology lecturer and creator of the Barista coffee Pinotage.

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Microorganism of the day: Schizosaccharomyces pombe

WHAT: a yeast that divides by fission (division in half, rather than budding like most yeast, hence “Schizo”), ferments sugars (hence “saccharomyces” or “sugar-loving”), and was first identified in African millet beer (hence “pombe” meaning “beer” in Swahili.)

Relevance to wine: S. pombe has traditionally been grouped among the spoilage organisms by the wine industry. Unlike its friendly, helpful cousin Saccharomyces cerivisiae (the major player in wine fermentation and bread making), S. pombe tends to throw off a lot of icky-tasting or -smelling byproducts as it turns sugar into alcohol. Sulfur is not a desirable aroma in wine!

S. pombe has one truly nifty feature; however, that is earning it a useful place in winemaking. It can ferment malic acid into alcohol. Malic acid is one of the three major acids in grape juice that carries over into wine (along with tartaric acid and citric acid.) Its fresh, fruity acidity is a boon in fresh, fruity wines, but too much and you’ll find yourself puckering.

The usual savior of malic acid overload is malolactic fermentation – conversion of malic acid into lactic acid by lactic acid bacteria after alcoholic fermentation yeasts have worked their magic. Great for rich, buttery wines — lots of unctuous flavors come along with the malic-to-lactic conversion — but not so great if you were going for a fresh and fruity style in the first place.

Could S. pombe help? What about the sulfur aromas and other issues?

A fair bit of research has investigated ways of using S. pombe in wine: to permit the inclusion of rotten grapes in Sherry and the potential of using genetic engineering to create a Schizoid-Schizosaccharomyces that keeps the good and does away with the bad, for example.

Lallemand, a major yeast company, has recently released ProMalic® “for naturally lowering juice acidity,” based on S. pombe. The yeast is submerged in the wine in something like a big yeast tea-bag, allowed to steep until your pH is up (and your malic acid down) to where you want it, and then pulled out before the yeast gets carried away with making other less-desirable stuff.

Some super-enthusiastic yeast folk from the Forsberg lab at the University of Southern California say that they have tried fermenting beer with their pombe with results that suggest skunk cabbage more than the local brewpub. With a respectful nod to classic eastern African beverages, however, they note that their attempts involved neither millet nor traditional methods. Anyone tasted any African millet beer?

Some home-brewers out there are apparently giving it a try: 

For the truly curious yeast fiends out there, see the Forsberg lab Pombe pages at for a truly excellent discussion of pombe in all its glory.

Erika Szymanski is a PhD student in microbial enology at Washington State University and an independent contributor to this blog. She is in no way affiliated with the sponsoring company. This blog was originally posted on her blog: The Wine-o-scope.

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