What role does alcohol play in wine?

“A woman drove me to drink and I never even had the courtesy to thank her” – W.C.Fields.

Is wine just a delivery vehicle for alcohol? What would wine be without it? Apart from the salubrious effects on our psyche, why is alcohol important in the life of a wine? It turns out that wine is an incredibly complex, dynamic equilibrium in which alcohol plays an intrinsic part. Although over 20 types of alcohol have been found in wine, the ethyl alcohol “ethanol” is most significant, and where I will focus. Let’s look at the many different ways alcohol contributes to the fundamental makeup of wine and our perceptions thereof.

In wine, yeast cells convert fermentable grape sugars into alcohol. Fermentation may be achieved spontaneously by yeast “bloom” present naturally on grape skins, or it may be induced by the winemaker via inoculation with a commercially propagated strain. Saccharomyces Bayanus and Saccharomyces Cerevisiae are by far the most important strains involved in wine fermentation. The end result is the effectively the same: sugar+yeast = alcohol+Carbon Dioxide (+heat). Thus, the quantity of potential alcohol is a direct result of how much sugar is available to the yeast in the grape must. Riper grapes are mainly the result of prolonged photosynthesis by grapevines due to high levels of sunshine. Of course if you don’t have enough, you can always chaptalise the must with an external sugar source such as cane or beet sugar. This assumes you make wine in a region where it is legal, say New Zealand or Canada, where it might be called “sunshine is a bag”.

During the maceration and fermentation process, alcohol plays a very important part in the final composition of a wine. The alcoholic fermentation produces important esters due to the presence of organic acids in the low pH medium of the fermenting juice. This process can be summarized by the simple equation: alcohol + acid = ester. These esters are often very volatile and contribute significantly to the aromas of any wine. Compounds such as methyl butanoate (pineapples), ethyl butanoate (bananas) and ethyl acetate (nail polish remover) are all produced as alcohol levels increase during the primary fermentation. Yeast strains can have a dramatic impact on ester production as well alcohol production and alcohol tolerance.

Alcohol is a potent solvent; therefore it has extractive qualities on a red grape must. Bitter and astringent flavonoids are particularly soluble as alcohol levels increase. In particular, leucoanthocyanins, catechins, and epicatechins can leach into the wine during maceration in the presence of alcohol. These compounds are mainly present in the seeds and stalks and their organoleptic properties can have marked effect on wine bitterness and astringency. Winemakers therefore, have to be very careful not to over extract these bitter compounds when the alcohol levels are high during the later stages of fermentation. Over the last 20 years many winemakers have exploited this knowledge with pre-fermentation (no alcohol) maceration pioneered in Burgundy. This “cold soak” occurs at +-10C for up to one week and allows anthocyanins to be extracted from skins without excessive bitterness. These compounds undergo some polymerization protecting and stabilizing them for later in the wines’ life. As the fermentation begins, the oenologist carefully manages physical agitation of the must, fermentation temperature and yeast vigour. Post fermentation maceration (with alcohol) is therefore a tricky technique which needs constant monitoring.

To understand the contribution of alcohol to overall wine quality it is important to look at what happens to a wine when the alcohol is removed. Wine without fermentation is simply grape juice. While pleasant, it exhibits none of the complexity or “joie de vivre” that we associate with wine. De-alcoholised wine can be achieved a number of ways with differing results in quality. Removing alcohol is usually a harsh process and therefore as a winemaker, one must never make the decision lightly. The simplest way is to add water to a finished wine. This technique dilutes flavour and quality accordingly. The next method is by a standard fermentation procedure followed by distillation of the product under a vacuum. Reverse Osmosis is the final way of de-alcoholising wine, and has become very popular due to the high quality wines produced. This technique is now commonly used in areas where wines with very high alcohol are unavoidable, such as California and Australia.

Overall, de-alcoholised wine flavour is altered significantly due to the tough mechanical process, as well as shifting the delicate ester equilibriums discussed earlier. Low alcohol wines are also particularly susceptible to microbial spoilage.

Alcohol is a potent anti-microbial agent and wine throughout history has been considered a “healthy” product, due to the fact pathogenic bacteria are unable to grow in the medium. The combination of low pH (3-4) and high osmotic pressure (alcohol) means that very few organisms can grow in this liquid. Alcohol tolerance in yeast has been improved by increasing sterol incorporation (oxygen) in the cell walls during hydration and through yeast selection. Alcohol acts as a preservative during the wine maturation process. Good quality Bordeaux, at say 13.5% alcohol, may have a shelf life of 50+ years. Madeira, at say 19%, may last 100+ years.

Alcohol affects wine organoleptically. Higher alcohol wines can make a wine smell “spirit-like”. They can increase the ratio of ethyl-acetate present, thus increasing perception of volatile acidity (vinegar). Lots of alcohol in a table wine can increase the “body” and “sweetness” of a wine. Interestingly this “sweet spot” may occur at different alcohol percentages (as discovered by people operating reverse osmosis equipment!). Alcohol also increases the perceived “warmth” of a wine. If alcohol is too high in a wine, it can taste “hot” or “burning”. High alcohol wines are therefore very difficult to pair with many foods. If a wine is too low in alcohol, the wine will taste “thin” or “watery”. Alcohol also amplifies astringency, bitterness and acidity. Thus, if a wine is too alcoholic, these other factors will increase the chance of a wine being unbalanced. Higher residual sugar can be utilised to counter this effect, such as in Port or Madeira.

Alcohol in wine is a social lubricant. Due to the interesting history, tradition and sense of place that wine possesses, it is already a conversation in a bottle. No other beverage pairs so well with western cuisine, where the whole experience is often more than the sum of the parts. Alcohol relaxes people; it makes them more likely to talk. It reduces inhibitions and creates atmosphere. While there are a multitude of health and social consequences around the issue of alcohol abuse, it is my opinion that the benefits to society far outweigh the downside. Moderate alcohol intake, especially when associated with wine has been found to have many health benefits. The unique combination of antioxidants and alcohol has been proved to lower rates of arteriosclerosis and heart disease, as shown by the famous study known as the” French Paradox”.

To conclude, alcohol is an integral part of the composition of wine and the how we enjoy it. We have explored the yeast fermentation process. We looked at the effects on ester formation and alcohols’ role as a solvent in phenolic extraction. The process of de-alcoholising wine and its’ consequences were discussed. Its’ role as an antimicrobial agent and the effects on wine ageing were also investigated. Finally we talked about the organoleptic properties and the social consequences of alcohol in wine.

Wine without alcohol is like boiled chicken. I like chicken, but why would you eat it that way when you could make a “coq au vin”? Alcohol affects the overall quality and potential of wine. Let’s face it; I’m not sure I would be here if my parents didn’t have a glass of Riesling to calm their nerves on that first date.