Winemaker musings
The Dry Finish; Why we dislike H2S
H2S (Hydrogen Sulfide) is a rotten egg gas. I suppose I could stop here and everyone would know why we dislike H2S, however its personality is a little more sinister.
A little Chemistry: In bottled wine H2S is a byproduct formed when there is a lack of oxygen. Young wines (especially reds) continue evolving in bottle and are hungry for oxygen so wine benefits if there is some dissolved oxygen available. Dissolved oxygen can be beneficial whereas leaving a wine open to the air oxidizes wine because the oxygen concentration on the surface is too high and the number of wine molecules in contact with it are too few.
When the concentration of H2S is high enough one quick sniff tells us ‘this wine pongs’! If the concentration is quite low it will simply mute the fruit and the wine will be drinkable but not very exciting.
Now for the sinister personality of H2S: A wine that has unacceptable levels of H2S can score quite high in a wine show, this is because H2S is very pungent at first but quickly deadens the sense of smell and we become less sensitive to it.
So in a lineup the first glass with elevated levels of H2S will be detected but the following wines with only slightly lower levels of H2S appear acceptable. Later when a show winner is evaluated on its own it can smell very ordinary.
Decanting a smelly bottle or vigorously swirling the glass to introduce oxygen will usually greatly improve wines showing mild levels of H2S.
The Long Dry Finish: Tannins
Tannins are a natural substance found in many fruits and bark of trees and are felt via our tactile senses rather than tasted. Most people are familiar with the tannins of over steeped tea or young red wines designed for long ageing.
Tannins in wine are derived from skins, seeds, stems (vegetative material) and oak. Depending on the molecule shape it can be astringent (drying) or bitter. In red wine tannin combines with pigment molecules to form larger molecules and feels astringent. In white wine tannin molecules are smaller and often appear bitter.
Tannins are extracted from the vegetative material over time by acid of the juice and alcohol of the fermenting wine. For this reason white grapes are rarely fermented in contact with any of the vegetative parts of the vine. Red wines become “softer” with age as it takes time for the tannin molecules to randomly bump into pigment molecules and form larger less bitter polymers.
Mature tannins are responsible for that wonderful velvety mouth feel of favorite red wines. In red wine we refer to bitter tannins as young, green, hard, coarse, aggressive, grainy (oak)… and astringent tannins as soft, silky, smooth, supple, dry, mature…
Winemakers can employ several different techniques to change the way tannin affects the wine:
When fresh juice is aerated some of the molecules causing bitterness are oxidized and precipitate to the bottom of the tank this can be a useful method in white varieties.
In young red wines oxygen encourages the polymerization of tannin and pigmented molecules and softens the wine. So we use various methods of introducing controlled amounts of oxygen into the winemaking process.
Fining of wines with additions of skim milk, egg whites, isinglass (ground up fish bladder), gelatin etc. selectively removes some of the tannin because tannins react with protein molecules. Laboratory trials are conducted to determine the fining agent and rate to be used. The protein of isinglass reacts with a different size molecule in the wine than say skim milk and if the wrong size molecule is removed or if too many molecules are removed the wine will appear harsher than the starting sample. When the correct amount of fining agent is used it all settles to the bottom of the tank and no traces remain in the wine.
The Dry Finish: Yeast Lees
Lees are the sediment at the bottom of a wine vat made up of things like dead yeast cells, grape seeds, pulp, skin fragments and tartrates.
Over time the yeast cells break down and this process termed autolysis releases nutrients into the wine which affect the smell, taste and mouthfeel. If wine is left on lees for a short period it will have a very subtle affect of adding to the roundness and creaminess of the wine. When it is left for long periods it will produce yeasty flavours of bread and vegemite as in bottle fermented sparkling wines that have aged on lees for several years.
Lees aren’t always a winemaker’s friend as it can produce off flavours of hydrogen sulfide (rotten eggs) and it can make a warm climate wine too heavy and overbearing.
But some judicious lees aging on crisp cool climate white varieties can make them very enticing.
If you have made it this far I’m not sure whether to congratulate you or suggest you get a life, try golfing, fishing or some therapeutic shopping.