by Jeff Miller, Artisan Family of Wines
[Photos by Jo Diaz]

 The question of alcohol in wine is both objective and subjective.  Objective in that its development can be explained and measured. Subjective in that it has a sensory impact on wine, which is always subjective.  I’ll deal with the objective today, and post the subjective part of this discussion later in the week.

First, the basics.  Wine grapes contain sugars (mostly glucose and fructose). Yeasts convert the sugar to alcohol and carbon dioxide (which is vented to the atmosphere) through a series of chemical pathways.

The amount of sugar in the grapes is measured in terms of degrees Brix, or more simply just Brix, which is the percentage of sugar in the grapes (e.g., a 25 Brix must contains 25% sugar).  As a rough rule of thumb, if you take the Brix of the grapes at harvest, and multiply by 60%, you will get some approximation of the final alcohol content (various other factors preclude an exact percentage calculation).  Therefore, grapes harvested at 24 Brix should end up around 14.4% alcohol; 27 Brix grapes should end up around 16.2%.

The riper the grape, the higher the sugar content (and ultimately the alcohol content) will be.  Not only does the additional time allow the vine to produce and transport more sugar to the grape, but the water in the grapes evaporates (a process called dehydration), increasing the percent sugar in the grape.

High alcohol is best thought of not in isolation, but as one of several characteristics of riper grapes.  Flavorwise, those grapes produce wines with more prune and raisin characteristics (flavors that develop later in the ripeness cycle) than do lower alcohol wines.  Lower alcohol wines, on the other hand, tend to have more green notes (characteristic of less ripe grapes), as are often evident in Bordeaux wines, and red wines from more northerly climates.  In addition, longer hang times result in lower acid levels.  Depending on your point of view, the effect of the riper grapes is appealing, or not.  We’ll get to this point later.

So, to summarize, less ripe grapes result in wines with lower alcohol, greener flavors, and higher acidity.  Riper grapes have more alcohol, more prune and raisin flavors, and less acidity.

Now all I’ve said so far assumes that you take the grapes in, crush them, and ferment them, without more ado.  But, in fact, there are two things that can be done in the winery to affect the final alcohol level.  The first is to add sugar (called “chaptalization”) to the must, which will increase the final alcohol.  This is common in Europe, where the grapes often do not reach the desired sugar level.  Generally, it is illegal in California.

The second thing you can do is add water, which, by lowering the overall sugar percentage, results in a finished wine with less alcohol.  Since alcohol becomes increasingly toxic to yeast at higher concentrations, a high alcohol wine runs the risk of a “stuck” fermentation, that is, a fermentation where the alcohol kills off the yeast before all the sugar is converted to alcohol.  So adding water reduces the final alcohol level in the finished wine, and therefore the risk of a problem fermentation.

While not directly relevant to alcohol levels, there is one other winery intervention that must be mentioned.  It is very common, in California, to add tartaric acid (the main grape acid) to the wine.  If done, this can compensate for the low natural acidity in very ripe grapes. 

So, at least in theory, you can take some very ripe, high Brix, low acid, grapes, add some water and tartaric acid, and end up with some of what you would expect from less ripe grapes. However, the flavor components cannot be altered the way sugar and acid levels can.  You’re pretty much stuck with those.  So if you taste a wine with prune and raisin flavors, but it has a lower alcohol level and reasonable acidity, there’s a good chance the winemaker has made adjustments to what was originally a high sugar, lower acid, must.

There is little question that Brix levels have risen over time.  When I first started drinking wine, an alcohol level of 12% was quite common (which would reflect a Brix level of about 20).  As we now usually pick later than was the case 30 years ago (and for other viticultural factors beyond the scope of this article), Brix levels have risen considerably.  It is now quite common to harvest grapes with Brix levels in the high 20’s.  Interestingly, reflecting this bygone era, the TTB, the Federal government agency which regulates much of wine production, has a cut-off between what it considers a “table wine” (below 14.1%) and what it classifies as a “dessert wine” (14.1% and above).  So while you may be drinking what we’d all agree is a table wine, Uncle Sam takes the view you’re drinking a dessert wine (which, by the way, means it can impose a higher tax rate).