There are a considerable number of wine faults and flaws which are common knowledge, such as oxidation, cork taint often referred to as corked wine, heat damage due to bad storage, etc. There are also many obscure faults that are dealt with in textbooks, and which may be found in home-made wines, but which are not common in mainstream commercial wines. Here, I shall endeavour to name some of the most important flaws and faults that might occur in wine not only during the production stage, that is, after the grapes had been harvested, but even slightly before, when the grapes are still on the vine. The main faults, but, do occur and develop during the production stage, and some even in the bottle.
Varietal Character or Fault:
Hydrogen Sulfide; Sulfides and Marcaptans.
Hydrogen sulfide formation, which if left untreated by the winemaker forms marcaptans. This gives rise to flavours ranging from rotten eggs to burned rubber, none of which are in the least attractive or desirable. With some wines it is a sign of their typicite', when the wine is still young, and once the wine age, in most instances, pure fruit aromas and flavours develop.
One of the prime sources of hydrogen sulfide is elemental sulfur. In many parts of the world, elemental sulfur is used extensively in vineyards to control powdery mildew or oidium. Sprays made out of a mixture of sulfur, lime and copper is a traditional spray which originated in France, and is commonly known as the Bordeaux Mix. This mixture is also used extensively in most wine-grape growing countries and regions both in the Old-World as well as in the New-World, as grape growers and viticulturists seek to pull back from the systematic chemical and bio-chemical sprays whose long term side-effects are uncertain and not really known. In this regard it is advisable that grape growers cease to spray sulfur at least one month before harvest.
Hydrogen Sulfide is produced to a degree in almost every fermentation. Even if no elemental sulfur is present. The yeast breaks down certain amino-acids and in the course of doing so triggers the formation of hydrogen sulfide. If the hydrogen sulfide is left untreated , it reacts with other chemicals in the wine to form, as has been said earlier, more complex sulfur compounds , usually referred to as marcaptans. These substances can be very difficult to remove.
Marcaptans in themselves are far more varied than hydrogen sulfide, and they assume an ungodly range of totally unpleasant personalities such as burned rubber, tar, rotten game, fowl manure, rancid garlic, leather, gravel to name a few, are some of the aromas, while the taste always has a bitter astringent finish to add to whatever particular flavour it may have.
Once bottled, certain types and styles of wine, have to be aged for several years in the bottle prior to release; but there are many wines that are released young for immediate consumption. The best way to make sure that the wine that you are about to drink,( unless it is an everyday, quaffing wine), is free from most of these gasses and substances, is to open the bottle a few hours before it is to be drunk and or better still to decant it, so that it will be given the opportunity to breath and dispose of all undesirable gasses to the atmosphere.
Is volatile acidity a fault or a virtue in a wine? It is well known that VA is present in all wine to a lesser or greater degree.
Volatility or the presence of acetic acid and ethyl acetate, is caused in three ways, at different times and different degrees. The initial level which is present in all commercial wines, stems from their inevitable formation as by-products of yeast activity during the primary fermentation. The next cause is the malolactic fermentation, and the last, and most destructive, is bacterial activity, which can be either lactic bacteria, and acetic bacteria, that in the presence of air, readily oxidise alcohol to acetic acid and ethyl acetate.
The level at which volatility becomes apparent varies with the wine. At low levels it manifests itself as a slight piquancy . As the level increases, the piquancy becomes sharpness, which might muffle other aromas. Finally if it increases it gets to a vinegary, fiery, sourly acidic finish on the palate, with a solvent like aroma.
Volatile acidity can be prevented through the use of reverse osmosis technology, which is also used to remove water from must or juice. It also allows the reduction of acetic acid to whatever level the winemaker stipulates.
Maintenance of adequate levels of sulfur dioxide, the exclusion of oxygen, cool to cold storage in casks, and an appropriate pH level will help prevent the development of unwanted levels of volatility. Once a wine is bottled, prevention of undue ullage (that is the space between the wine level in the bottle and the cork once pressed in place), together with good storage, under stable, cool conditions, will protect it.
There are two principal types of oxidation: Chemical and Micro-Biological.
Chemical oxiditaion is a two-stage process. First, oxygen is taken into and dissolved in the wine. Depending on a number of factors, it will then slowly or quickly, as the case may be, react with phenols in the wine, causing chemical changes, principally seen as a loss in aroma, flavour, colour change, and degradation.
Micro-biological oxidation is caused by bacteria, which might also be present during the process of chemical oxidation and results in additional chemical or biological changes.
Oxygen can be absorbed by wine in almost any circumstance in which it is brought into contact with it. Any handling involving movement or agitation will have this effect. Racking, filtration (if misused), and transport are three examples.
An oxidised wine may partially briefly recover, but its ultimate demise will be hastened significantly and it will never approach its true potential.
Oxidation is one of the least forgivable faults in red wines, simply because it can so easily be prevented.
Brettanomyces or "Brett":
In the last three decades, a number of seemingly, unconnected developments have occured that have made "brett" the most common spoilage factor in wine.
First, there was a move toward higher natural alcohol in the wine of most wine-making countries, especially those obsessed with achieving high scoring points from the international wine critics.
Second, is climate change, and canopy manipulation, and picking of the grapes at a later date than normal, so that natural sugar concentration is increased.
Thirdly, is the use of highly efficient cultured yeast.
The internal relationship of some of all these factors varies from place to place, region to region, country to country. Elevated levels of alcohol in high quality wines are a matter of concern as not everyone likes, dense, full-bodied, rich, alcoholic wines, being either red or white.
Main response to solve these problems is to harvest the grapes earlier in the season, and to move to lower levels of sulfur dioxode additions. Cork permeability, that is the extreme variability in the oxygen permeability of one-piece natural corks, and thence their inability to retain near-constant levels of sulfur dioxide SO2.
Cork and Cask molds:
The weak point and main fault of the cork and some oak casks is trichloroanisole (TCA), which imparts a musty, moldy aroma and flavour. Everyone can, within reason, recognize a grossly corked bottle of wine. Winemakers accept the fact, that a significant number of their wine bottles, will be found wanting by consumers. Consumers might not realize that the faint bitterness they taste in wine is in fact cork mold. A croked wine will have a musty, wet-carpets type smell, and the taste will invariably be flat. About 3 to 7 per cent of all bottled wine is found to be corked.
If a wine batch is affected by cask mold, this in all cases should be recognized and found out by the winemaker prior to bottling. Once discovered to contain this serious fault, the wine must be disposed of down the drain. TCA taint cannot be removed once it has taken hold.
Another taint is mousiness, which is formed by certain types of lactic acid bacteria, which may work symbiotically with Brettanomyces, and which produce a nearly identical mousy smell.
To prevent either of the above, proper levels of sulfur dioxide have to be maintained both in the casks as well as in the bottle.
Let me make one point very clear: by Reduction we do not want to mean a reduction in the ullage, that is the level of the wine, in either casks or bottles. It is much more technical than this.
Reduction is a chemical reaction that is in effect the complement of oxidation and one in which an element or compound gains electrons. The essential feature of oxidation is, that electrons are transferred from the component being oxidised to the one being reduced. That is, to have a reduction, something else must be oxidised.
Wine in a stoppered bottle or other airtight container is said to be in a reductive state because any reaction that takes place within it reduces the possibilities for further change by using up some of the available oxygen.
Reduction has become a much debated topic in the wine trade since the more wide-spread adoption of tin-lined screw-caps as closures. These make a near impermeable seal which prevent the entry of the miniscule amount of oxygen that can be permitted by a cork closure. But, it must be pointed out, that reduction is not unique to wines stoppered with a screw cap. The gas impermeability of very good cork stoppers has been shown to be as good as screw caps. Reduction characters can therefore appear in a wine regardless of the closure, unless the characters have been prevented or removed during the wine making process, as explained in preceding headings in this feature.
Hydrogen Sulfide, Marcaptans, Thiols, etc., tend to form under reduction and therefore the foul smells described earlier under these headings, can be detected when "Reduction" in a wine bottle has taken place.
Fragments of cork which might be caused whilst openening the bottle is neither a wine fault nor is it a flaw.
Sediment in the bottom of a wine bottle is not a fault nor is it a flaw.
Wine diamonds which are deposits of potassium bitartrate crystals that form at the bottom of bottles of some highly rated white wines, is not a fault. These diamonds are not sand, glass or any other lethal substance or signs of incompetent winemaking. They occur naturally in certain wine styles, and might in most case dissipate with age. But nevertheless if found, they are not considered to be faults or flaws.
Wine sparkles, spritz or petillance, is normally tolerated in most aromatic, light-bodied wines; are frowned upon in full-bodied whites; and rejected in red wines.
If this is caused by a secondary, probably malolactic fermentation in the bottle, this is totally undesirable. But if it's just carbon dioxide it might not be a fault as this is normally removed naturally by aging in the bottle.
Most wine tasters, alas, do not take the latter into consideration and just put the blame on the secondary fermentation which would automatically condemn the wine as faulty. Education and experience is required here.
There might be others which some of you might have read about in books, but the above illustrate the most important faults and flaws in wine. The best, commercial winemakers, even the mainstream ones, take very careful steps to avoid these faults during the production process, and the improvements in both viticulture as well as oenolgy knowldege have to a very large degree improved the science of winemaking from the soil and vineyard direct to the bottle to give consumers a near perfect bottle of wine.