2.15 Wine Faults and Flaws

So far we've discussed the characteristics of wine which develop when things go to plan in the winemaking process, but what sort of aromas and tastes are present when things go awry? Since the undertaking is a long and complex one, there are many possible causes and sources for undesirable flavours. Even trace amounts of certain compounds can be sensorially potent. When unwanted odours and flavours over power or diminish a wine's latent flavours, the consensus is that they be considered 'flaws' or 'faults'. However, if they remain subtle and in balance with other elements in the wine, the same 'flaws' can actually be considered 'complexing factors', hence the ongoing debate amongst winemakers, critics and consumers. Faults become a question of wine style - grape rot isn't a bad thing if you're making sweet whites, and bubbles in Champagne were not at first a conscious development, rather the result of spontaneous re-fermentation in the bottle.

At the end of day it's perhaps best to think of wine like food. And just like food, grape juice is susceptible to the effects of spoilage from the point of harvest, up to and even after bottling. Nowadays, as in the food industry, the final arbiter is more often than not the laboratory, an essential part of quality control for any modern winery. There, winemaker's can "put a number on things" and employ some sort of normative standard for measuring when a fault is a fault before deciding how to remedy it, or in the worst case scenario, withdraw the product from sale.

1. In the Vineyard.
The most ubiquitous threats throughout the life of a wine are oxygen and microbes, often working in tandem. In much the same way that an apple left open on the kitchen bench turns brown, there is no way of turning back a wine that has been over exposed to oxygen. Not surprisingly the mechanisms for initial oxidisation in apples and grapes are the same. It involves a pesky enzyme known as Polyphenol oxidase (PPO).  PPO evolved alongside and inside many fruits (including grapes) as a protective mechanism against bacterial spoilage. Thus, when the skin or flesh of an apple (or a grape) is damaged, the PPO enzyme is exposed to air. The discoloured (bruised) area that we can see has actually been converted by PPO into an environment toxic to many invading bacteria. It is nature's first point of call to save the fruit. 

In a winemaking context this rapid, enzymatic oxidisation can be desirable and even encouraged - think Chablis or many white Burgundies.  It's in part what bestows these wines with nutty, apply characteristics. However, when the aim is to create fresh, aromatic, new world styles - Marlborough Sauvignon Blanc for example, the results are less compelling. One only needs to imagine how apple juice made from bruised apples left on the bench might taste. Essentially, the lively citrus and passion fruit aromas deemed desirable in the Marlborough Sauvignon Blanc are very readily oxidised. This leads to flat and subdued aromatics on what a drinker expects to be lively and aromatic wine (just like that bruised apple). Such oxidative enzymatic spoilage usually results from poor fruit handling during and after harvest, and a failure to protect the fruit and must from oxygen.

The other prime microbial danger in the vineyard is the fungusBotrytis cinerea(derived from the Latin for "grapes like ashes"). Think of the ugly grey mould sometimes seen on a poorly stored punnet of strawberries. It's the same mould in action. It can take two forms in the vineyard - noble rot (where individual grapes are affected) and bunch, or 'grey rot' (where the whole bunch rots, usually from the inside out). The first form is desirable for the classic sweet wine styles of Sauternes and Barsac whereby botrytis action dehydrates the grape and concentrates sugars; the second results in the complete loss of fruit. Or if its presence is undetected at harvest, it can go on to contaminate the resulting juice causing a 'mouldy taint' and interfering with yeast in the fermenting must or juice, making clean and complete fermentation difficult. The stressed yeast produce higher levels of sulphidic compounds causing a range of off taints (discussed further on).  More insidious however is botrytis' partner in wine crime, the enzymelaccase

Laccase is a copper carrying enzyme (copper being a strong catalyst for oxidization) secreted by the botrytis spores into the flesh of the grape.  It is resistant to sulphur dioxide and active in wine even after bottling.  It speeds up the oxidization of wine, causes browning in red wine and accelerates the production of volatile acids.  The only way to nullify laccase contamination in must, juice or wine is the very undesirable process of pasteurisation (heat treatment).

The discussion has so far centered on the primary effects of oxidization as facilitated by microbial contamination of fruit in the vineyard or before fermentation.  The key indicators are a loss of freshness and a negative impact on colour. It can get worse as the oxidization of wine only stops when there is nothing left to oxidise. The end point for all great wines is vinegar.

2. In the Winery.
The major culprit for wine in tank and bottle isacetaldehyde, a compound responsible for green apple through to nutty flavours. Typical acetaldehyde levels in red wines are around 30mg/l, whereas aged sherries can contain 300mg/l or more.  In high concentrations it's this compound that makes table wines turn fino sherry-like or 'aldehydic'. (Our sensory threshold for the compound is around 120 mg/L). Acetaldehyde is formed in wine by a chemical oxidation of ethanol by free oxygen molecules sometimes aided by microbes (see above) and/or chemical catalysts (e.g. copper) For a sherry-style wine, a degree of controlled oxidation assisted by microbes is desirable, whereby "flor" or film of yeast cells internally oxidize ethanol and produce acetaldehyde.

Filtration to remove the bacteria causing the acetaldehyde problem can go some ways to remedying the fault, but prevention is the best cure and relatively straightforward. Using an inert gas blanket such as argon, nitrogen and/or carbon dioxide, winemakers can displace oxygen from any empty space in storage tanks to form an efficient oxygen proof cap over the wine. (Argon gas based 'Wine Preservers do exactly the same thing). Another technique is keeping the wine cool at all times (because wines exposed to high temperatures will also oxidise more readily) and/or by adding chemicals, such as ascorbic acid and sulphur dioxide that inhibit the activity of organisms and enzymes which react with air.

Careful handling and clean wineries are essential in modern winemaking, but sometimes winemakers themselves are the cause of unpleasant aromas. Adding too much of the preservative sulphur dioxide can have disastrous consequences leading to burnt rubber, burnt matchstick or mothball aromas and "hard" mouth feel in wines. (See the chapter 'Sulphur Dioxide' for more).

A second additive that can either make or break the final result is Potassium sorbate (sorbic acid). Sometimes used as a preservative against yeast spoilage,  when it reacts with bacteria found in lactic acid during the fermentation process, a curious aroma of crushed geranium leaves will result - aptly known as 'geranium taint'.

Dimethyl sulphide is yet another sulphur-based compound that occurs naturally in most wines, and can either enhance a wine's fruitiness, fullness and complexity - or in excess contribute cooked cabbage, canned corn and asparagus flavours.

Particularly foul, is Hydrogen sulphide (H2S), the compound that can give wine a distinctive rotten egg aroma. It is another compound that may be formed as a by-product of yeast fermentation when certain contaminants are present, if there's too little nitrogen present in the juice or must, or if the fermenting yeast receive too little oxygen (fermentation is the one stage of the process where oxygen is always welcome!)  Hydrogen sulphide can be easily dealt with by introducing a lot of oxygen very rapidly into the wine, juice or must.  

When hydrogen sulphide combines (over time and usually in the bottle)  with ethanol and some amino acids in the wine, it yields compounds called thiols (ethane, methanetiol) otherwise known as 'mercaptans' and, as they continue to join together they become complex mercaptans. Their rubbery or onion, garlic-like aromas take the wine to another level of smelliness. While hydrogen sulphide can be alleviated via a small addition of copper sulphate, or a splash of fresh air the mercaptans are here to stay. Clean, healthy fruit, moderate fermentation temperatures and ample nutrition for yeasts and immediate removal of any H2S are the only ways to avoid this stinker.

Many serious pit falls in making good wine can also be avoided by ensuring a strong primary and secondary fermentation. These are keys to avoiding excessive volatile acidity (a measure of all the steam distillable or volatile acids in a wine). While volatile acids are naturally present in all wines in concentrations ranging from 0.5g/L to 0.75 g/L, in greater concentrations (>1.5g/l) they adversely swamp wines with vinegar (acetic acid) and its associated aromas and flavours.

The next level is the esterification of ethanol and acetic acid to form Ethyl acetate. This is typically caused by yeasts during the fermentation process or from catalyzing bacteria associated with acetic acid in the wine, when combined with excessive amounts of oxygen. Ethyl acetate is a primary ingredient in nail polish and nail polish remover and the aroma presents as such when at excessive levels.

One of the more controversial wine flaws is the presence of brettanomyces (often referred to as 'brett'). These yeasts are notable for their distinctive barnyard, earthy, iodine and even fecal scents. Usually referred to as a 'spoilage' yeast, brettanomyces' presence may indicate less than perfect hygiene in the winery, though more often poor maintenance of wine pH (brett cannot live in a low pH environment).  It isn't always shunned by winemakers or consumers, hence the controversy. The earthiness can balance nicely against a wine's fruitiness. Higher levels deliver intimidating horse saddle, wet dog, fresh manure or band-aid notes.

Brettanomyces has the ability to subsist on residual nutrients even after all the fermentable sugars are gone and it ferments very slowly.  What was an appealing nuance at bottling can become just plain feral after a year or two in the bottle. Combined with a wildly varying tolerance to these compounds amongst individuals it is not surprising it is a polarising trait.

Brettanomyces is symbiotic to grapes and pretty much ubiquitous in wineries in regions with a history of wine production. Strong winery hygiene can only go so far in limiting the damage from this little monster. Sterile filtration can exclude the yeast from wines, but the best defence is to maintain a wine environment hostile to the organism - low pH and correct levels of free sulphur dioxide.

3. After bottling.
So far we have concentrated on faults that occur during the wine making process; however some faults can occur once the wine has been bottled. The most notorious is cork taint. Until recently, the boiling and bleaching of cork planks often took place in a strong hypochlorite solution which inadvertently contributed to potential taint by providing a ready source of chlorophenols for use by micro-organisms. Phenols in the cork reacted with the chlorine to form a chemical compound called trichloropherol, which in turn was converted by microbes in the bark to trichloranisole (TCA). Cork taint is actually a misnomer.  TCA can be produced wherever chlorine comes in contact with wood - wine barrels and wooden vats as well!

At bottling, the wine comes into contact with the compound, first deadening fruit flavours, flattening textures and in sufficient quantities, forming musty, mouldy, sweaty sock / wet newspaper aromas. TCA can be detected in dry white wine and sparkling wines at levels around two parts per trillion (0.000000000002 grams in a litre of wine).  It's often cited as a major reason for the introduction of screwcap bottles and synthetic corks, however the alternative closures are significantly cheaper and now accepted by most consumers. The economic incentive for winemakers to make the switch is obvious - less cost, less waist, less undeserved consumer dissatisfaction.  Keeping chlorine out of the winery environment is essential to minimising TCA - from cleaning agents to air fresheners and even the mains water source - not to mention the screening of incoming cork lots, both chemically and sensorily.  (See the chapter 'Corks & Cork taint' for more, plus a simple trick that can ameliorate cork taint.)
A less troublesome external factor is ultraviolet light.  'Light strike' causes unpleasant aromas that are typically described as wet wool and wet cardboard. Interestingly, it seems that light-coloured, delicate wines such as Champagne are at most risk from this kind of damage, whereas red wines are rarely affected due to the presence of phenolic compounds. Wines are often bottled in coloured glass and stored in dark locations to limit UV light. 

Clarity, lack of which nowadays is always considered a fault in young wines, is important in that it can provide insight into a wines condition and stage of development. Alternatively, a slight haze may indicate that a wine has been left unfiltered in order to maximise flavour, as is often the case with Pinot Noir. (The suspended particles settle down if the wine is left to stand in an unopened position for 48 hours prior to serving). However, consumers generally expect a completely clear beverage - there is a perception that whatever has caused cloudiness will also have impaired the wine's overall quality, hence considerable effort is usually undertaken in the winery to produce a wine that's stable in terms of clarity.

In table wines, especially whites, a haze may occur during storage in warmer than normal conditions. Proteins in the wine coagulate, precipitating as a visible haze indicating that the winemaker has not 'heat stabilized' the wine. Adding bentonite (a clay that acts as a clarifying and settling agent) before bottling usually avoids the problem.

If a white wine has not been cold temperature stabilized, then it's also more likely that tartrate crystals will condense, become heavy then fall out of the wine creating sediment in the bottle that's often mistaken for small pieces of broken glass. These may be present under the cork or in the bottom of the bottle.

The crystals and protein haze described above have minimal impact on wine flavour (less than the processes required to prevent them) so for many wine makers (and some educated drinkers) this is another fault that falls into the contentious category.

Sprightliness or chains of bubbles are certainly expected to be present in Champagne or Methode Champenoise; however they can make an unwanted appearance in wines that were intended to be still - both red and white. This is usually caused by wine being bottled before excess carbon dioxide has had time to escape, but may indicate a more significant problem.  A tertiary fermentation due to actively fermenting 'malo' bacteria, our old friend brettanomyces or simply re-fermentation of residual sugar are usually the culprits.  While every sparkling wine style around today is most likely the result of just such an 'accident' it is critical for modern winemakers to control spoilage organisms at all stages of the process.

We've outlined some of the most commonly accepted wine flaws and faults. There are others. Thankfully, given the comprehensive advances in education, viticulture, winemaking, sanitation and science, nowadays you're unlikely to experience many of these outside of a winery. Fueled by international criticism and increased competition, wine quality has increased to such an extent that serious faults or even slightly flawed wines rarely make it to market. If more wine lovers could only remember just how common bad bottles of wine used to be, (even only several decades ago), we'd realise this is an achievement that's worth drinking to.