Issue link: https://digital.copcomm.com/i/637107
{ SOMMjournal.com } 1 1 1 WINE IS, FOR THE MOST PART, WATER AND ETHANOL, which in turn become vehicles for the minor components that are largely responsible for aroma, taste and texture. Through the efforts of researchers at the University of California at Davis and the University of Burgundy in Dijon, our understanding of wine's biochemical landscape is expanding rapidly. Research focusing on metabolites known as metabolomics, the scientific study of the set of metabolites present within an organism, cell or tissue, has now validated the concept of terroir by showing that every vineyard and every wine has a fingerprint that, like our own, is utterly unique. At the metabolic level, wine contains a record of how it was made—a fingerprint that points to the origin of the oak and "memories" of sulfur dioxide additions that were made to the must. But let's not get ahead of ourselves. Beyond general references to tannins, acids and sugars, the lesser elements of wine are usually left to their own devices. Knowing what constitutes those compo - nents and how they collectively contribute to wine quality or in the case of flaws and faults undermine it is key to understanding what's happening in your glass. Ethanol is the major, but not the only, alcohol found in wine. The higher alcohols isoamyl and isobutyl are larger molecules than ethanol and in excess they smell like banana and contribute bitter, burnt flavors. Alcohols can increase the perception of sweetness, but when wines are imbalanced to alcohol they are referred to as being "hot." There are a handful of culprits, including yeasts, bacteria and material other than grapes (known as MOG), that are respon - sible for bitterness that detracts from wine quality. The fault known as amertume (French for bitterness) stems from the combination of glycerol, a sugar alcohol (polyol) without color or aroma that contributes to body, and lactic acid bacteria. Glycerol is joined by mannitol and sorbitol, the minor sugar alcohols most commonly used as artificial sweetners. The simple, six-carbon sugars glucose and fructose are present in equal amounts in grapes and compose up to 25 percent of grape pulp at harvest. Consumed by yeasts during fermentation, glucose and fructose can be found as residual sugar in wines that haven't been fermented to dryness but not all sugars in grapes are fermentable. The five-carbon sugars arabinose, rhamnose and xylose are still present in wine after fermentation. Wines fermented to dryness usually contain between two and five grams per liter (g/l) of residual sugar with 3.45 g/l being the average threshold for the perception of residual sugars in dry wine. Acids, the components that enervate wine, come in two basic forms: fixed and volatile. We're familiar with the fixed acids malic, tartaric, citric because they're commonly used to make adjust - ments to wine. In red wines and, when the winemaker chooses, in whites, malic acid also undergoes the conversion from a fixed acid to volatile lactic acid during malolactic fermentation which, techni- cally, isn't a fermentation, it's a bacterial cell respiration. Volatile acids including lactic acid, acetic acid, ethyl acetate and post-fermentation butyric acid are those that can volatize or become gas at room temperature. They in turn combine with alcohols to form esters, aroma compounds like apple peel, strawberry and pineapple or ethyl butyrate, the combination of ethanol and butyric acid. Wine acquires secondary and tertiary flavors as esters form, split and concentrate in an effort to reach a state of equilibrium. So, in theory, a fully-developed wine would be one that has reached a state of molecular equilibrium. Even the savory flavor of umami is attributed to an acid, the amino acid glutamine, which along with proline and alanine make up the bulk of the amino acids in wine. Above threshold, volatile acidity, the total concentration of vola - tile acids in wine including acetic acid and ethyl acetate, is at best a flaw and at worst, a fault. But even a wine that's in good condition typically contains between .3 –.6 g/l of acetic acid and, in small amounts, ethyl acetate which is described positively as a balsamic character in wines like Chianti and Amarone della Valpolicella. Wine is chock full of potassium and also contains sodium, calcium, magnesium and phosphorous—minerals that fuel the debate around the perception of minerality, the source of which increasingly points to acids. Wines with high levels of malic acid exhibit minerality, as do red and white wines with succinic acid, which has a salty taste described as mineral. Having debunked the misguided notion that geological minerals are the source of miner - ality, researchers now point to a combination of factors from the chemical balance of the soil, viticultural practices and winemaking choices that account for minerality. The family of minor compounds that are responsible for color and have a significant effect on taste and mouthfeel in wine are known as phenols. There are two groups of phenols: those that originate from the grape skins and seeds, including tannins, anthocyanins and flavo - nols, forming the group known as flavonoids; and the non-flavonoids, among them resveratrol, phenolic acids, wood tannins (ellagitannins) and the volatile phenols like vanillin and compounds associated with Brettanomyces. Over time, the flavonols in white wine interact with oxygen to cause browning, while color degrades in red wine as anthocyanins interact with tannins and catechins. Last but by far not the least problematic, these two naturally- occurring compounds only become a concern when they are per - ceived above threshold: acetaldehyde resulting from the partial oxidation of ethanol, which causes flattening of flavors; and sulfur dioxide, a by-product of the fermentation process, which is pres- ent as organosulfur compounds like mercaptan thiols (skunk) and disulfides (garlic). Oxidation and sulfur in all its forms will be the focus of future columns. KNOWING THE LESSER ELEMENTS OF WINE IS KEY TO UNDERSTANDING WHAT'S IN THE GLASS BY DEBORAH PARKER WONG