The other day I came across this fact sheet: “Reducing Alcohol Levels In Wine” published by the Australian Wine Research Institute (AWRI). Directed at the professional winegrower, this is the best agenda-free piece on wine alcohol levels I have read, period. It’s worth the interested reader’s time.
All of my own efforts to manage alcohol levels in our wines are mentioned here. In the vineyard every year we reduce canopy leaf area to balance crop load, and I have found that irrigating to 85% of evapotranspiration demand right up to harvest prevents runaway sugar accumulation. I have always disdained wines with over-ripe flavors, and so have always picked at the earliest date that I find the various components of the grape to be quote-unquote “ripe” – a personal definition, but one that I am happy with.
I found it amusing that the AWRI paper discusses water adds under the heading of “blending.” Adding a “reasonable” amount of water, for one reason or another, is a common practice in winemaking. We just don’t talk much about it.
I was left scratching my head over the mention of glucose oxidase to decrease the level of fermentable sugar in juice or must. I recall reading a few research papers in the 1990s about this, but didn’t think the technology ever made it out of the lab. I honestly don’t know of any winery that uses this enzyme. Nor have I ever come across a commercial preparation for use in wine. So, pace, “natural” wine aficionados.
Fermenter design does make a difference. I prefer to use fermenters with a must depth of 38″ during peak fermentation, regardless of diameter, and seek to achieve peak fermentation temperatures of around 90° F for my red wines. I have empirical evidence that this approach reduces our so-called “conversion ratio” (the percent alcohol immediately after fermentation divided by the Brix before fermentation) by up to 5%.
By contrast, I have found no consistent evidence that yeast selection has any effect on alcohol level. Whether I conduct a ferment without inoculation, or by inoculation with a selected commercial strain, the final alcohol is the same within measurement error. Incidentally, these days I start every fermentation without inoculation. If the initial Brix is high or if the ferment shows evidence of stress, I inoculate with a commercial strain I feel most suited to the variety. In effect, all our ferments are conducted by mixed strains of yeast.
The AWRI paper discusses the most obvious, the most used, and the most discussed (and often reviled) method of alcohol level management: physical removal of alcohol from finished wine by reverse osmosis or vacuum distillation. I have experimented with these methods on a limited basis with mixed—mostly negative—results. My biggest concern with large-scale alcohol removal is that the wine is nearly always rendered “hotter” by the treatment. I speculate that this is due to removal of ethanol at a faster rate than alcohols of three carbons or more by the processes.
The article mentions de-alcoholizing small parcels of wine and blending back. I have had some good results with this approach and I am experimenting with this method on an ongoing basis, because of the next topic discussed in the article: loss of alcohol by evaporation during barrel aging.
In fact, during barrel aging in our cellar the alcohol level of the wine increases by up to 1.2%-1.5% over two years. During barrel aging, the wood of the barrel acts as a semi-permeable membrane. Wine components inside the barrel migrate through the wood at various rates and evaporate from the outside surface. My a priori assumption is that the rates of migration of water and alcohol are dependent on the differences in concentrations between the inside and outside of the barrel.
Let’s say I put a wine to barrel at 13% ABV; this wine is approximately 87% water. In our barrel cellar, the concentration of alcohol in the air is essentially 0%, while the relative humidity averages about 35%. Water leaves the barrel faster than alcohol because 87%-35%=52% is four times greater than 13%-0%=13% (52/13=4); therefore, the thermodynamic drive for water to leave the barrels is 4x the impetus for alcohol to escape.
The AWRI paper discusses how alcohol levels decrease over time when the average relative humidity of the barrel cellar is 70%-90%, but also discusses the negative issue of mold growth in the cellar in this wet environment. Our barrel aging area was not designed to be wet, and we also store cased goods in proximity to our barrels. Humidification of our cellar is not an option.
My intent is to experiment with vacuum distillation of the wine I use to top our barrels. If we decrease the alcohol level of the topping wine, I believe we can slow the rate of alcohol increase in our barrels over time in our dry cellar environment.
Wine odor is one of the key markers of wine quality and, as a part of my series on wine quality, I have set myself the task of identifying and characterizing the sources of wine odor and showing how the interactions of these odor components aid in the perception of wine quality.
Wine is aged in wooden barrels to: (i) enhance its flavor, aroma, and complexity through transfer of substances from the wood to the wine; and (ii) allow gradual oxidation to occur. As a result of its “strength, resilience, workability, and lack of undesirable flavor,” oak is the wood of choice for most wine cooperage applications.
The oak used in the maturation of alcoholic beverages fall into one of three species: Quercus alba, Quercus robur, and Quercus sessilis. Q. robur and Q. sessilis, and their respective subspecies, are European white oaks while Q. alba is the source of 45% of the white oak lumber produced in the US. American oak used in barrel production is sourced from Kentucky, Missouri, Arkansas, and Michigan but there is no apparent regional distinction. European oak, on the other hand, may have designations which reach all the way to the forest from which the oak originated. For example, French oak from the department of Alliers may be sourced from a forest named Tronçais.
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Blog sourced from Wine — Mise en Abyme
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
“I have walked across the surface of the Sun. I have witnessed events so tiny and so fast they can hardly be said to have occurred at all. But you, Adrian, you’re just a man. The world’s smartest man poses no more threat to me than does its smartest termite.” – Doctor Manhattan
The above quote by Doctor Manhattan from the 2009 movie, Watchmen, made a very big impact on me. Not only did Doctor Manhattan have extraordinary physical capabilities, but also boundless intelligence and wit. Most scintillating however, was his ability to observe and control miniscule atomic particles and impossibly fast to imagine metaphysical events. Doctor Manhattan didn’t really strike me as a lush, but I’m sure that he would have been fascinated with the chemically complex and ever changing matrix that is maturing wine.
As a former minor winemaker at quite a few cellars, my favorite place has always been the barrel maturation cellar. Barrel ageing is ostensibly one of a wine’s more important stages of evolution before bottling. But how exactly does wine change during barrel ageing and what effect does it have on the countless chemical reactions taking place in wine every second? The main effect of oak barrel ageing is twofold. Wood character is introduced (the rate and intensity is mostly dependent on fill status of the barrel) and oxygen is very slowly introduced to the wine. Generally speaking, this results in softening of the harsh tannins and flavors present at the end of fermentation. Oak is a fascinating substance, which has a profound and remarkable effect on the flavor chemistry of wine. Key oak derived compounds are tannin, lignin, cellulose and hemicellulose.
Tannin plays a vital role in barrel ageing. Although most tannin in wine comes from the grapes, some of it is also liberated by the barrel during ageing. So what exactly is the deal with tannin? An experienced winemaker will instinctively know how to optimally merge and balance the tannins extracted during the youthful stages (fermentation, skin contact and pressing) and the mature stages (barrel ageing and blending). For instance, more tannic grape varieties such as Tannat, Cabernet Sauvignon, Nebbiolo and Shiraz cannot be approached the same as the less tannic Pinot noir. Once again, winemaker experience is paramount.
OK, now hold on to your chemistry hat, here comes the hard (but interesting) bit! Phenolic compounds (consisting of natural phenols and polyphenols) in wine are largely responsible for imparting taste, colour and mouthfeel to wine. They include phenolic acid, stilbenes, flavonols, dihydroflavonols, anthocyanins, flavanol monomers (catechins) and flavanol polymers (proanthocyanidins). Natural phenols can be separated into flavonoids and non-flavonoids. The latter group includes stilbenoids such as resveratrol and phenolic acids such as benzoiz, caffeic and cinnamic acids. The former group includes anthocyanins and wait for it… tannins!
What would a good red wine be without vanilla flavors, sweet and toasty aromas and notes of tea and tobacco? Specific compounds create these nuances in finished wine, for example: volatile phenols containing vanillin; carbohydrate degradation products containing furfural, a component yielding a sweet and toasty aroma; “oak” lactones imparting a woody aroma; terpenes providing “tea” and “tobacco” notes, and hydrolysable tannins, which are important to the relative astringency of the wine. Take note, every time you’re quaffing a wine (hopefully a worthy vintage), you’re consuming everything you’ve just read above. If this doesn’t sit quite right with you, then I guess nothing much will.
They say you should have respect for your elders. So, tread lightly the next time you pass through a barrel maturation cellar. You might even see Doctor Manhattan skulking around in the dark, silent corners…
Bernard Mocke is a technical consultant for Oenobrands.