Spotting a faulty wine is one thing, but where to lay the blame?

Spotting a faulty wine is one thing, but where to lay the blame? "Off" wine can result from the whims of Mother Nature, factors that man has little or no control over. Often, however, mistakes and "enemies" in the vineyard and cellar can be avoided, controlled or eradicated by the farmer or the cellarmaster, depending on the nature of the beasts - quite simply, bad wine is regularly a case of bad winemaking. Not forgetting, of course, that there are instances where the buck stops with you.

SCIENCE & BIOLOGY

acidity . . . Only a negative in wine when there's too much or too little. Numerous acids occur naturally in grapes - tartaric, citric, acetic, ascorbic (vitamin C), malic, lactic - and often more is added during the winemaking process. Acid serves as a preservative and is essential for lively wine (freshness), shaping its flavours and contributing to its length.

bacterial spoilage . . . Microbial spoilage can happen when, for example, the yeasts haven't all been removed or killed after fermentation, or if the wine hasn't undergone malolactic fermentation (before bottling), which can result in a secondary fermentation in the bottle - which in turn can lead to excessive carbon dioxide or alcohol in the wine, sediment and a mouldy characteristic.

brett . . . Short for brettanomyces, a type of yeast or mould that spoils a wine when its smell and taste become too obvious. Sensory descriptions range from "earthy" and "leathery" to "Band-Aid" or "Elastoplast", "burnt plastic" and "dirty mouse-cage". That said, it can contribute to the complexity of a wine when present in small amounts. It is believed that brett is harboured in or on wooden barrels and becomes problematic in unhygienic cellar conditions.

dirty cellars . . . Unhygienic conditions in the winery make for ideal homes and playgrounds for a whole host of bugs that can infect or affect a wine.

mercaptans . . . Can be formed when alcohol reacts with hydrogen sulphide - the "rubbery", "old sulphur" or "bad eggs" smells encountered in over-reduced (very de-oxygenated) wines or very old white wines that are past their best. Also described as smelling of garlic, onion, stale cabbage.

oxidation . . . The effect of exposure to air, oxidation amounts to a chemical reaction between the oxygen and the wine that changes the colour, smell and taste of the wine. Oxidised wine follows excessive exposure to air, which results in a loss of freshness and fruit character (when the wine becomes stale). Very oxidised wines take on an amber or brownish colour, sometimes tasting Sherry-like. Conversely, too little oxygen can result in reductive odours. All wines are oxidised to some extent: the level of oxidation must be controlled to produce a good wine, and the rate of oxidation thereafter must be controlled for good maturation.

PCA . . . Pentachloroanisole, related to TCA, is a chemical compound usually associated with wood that has been treated with pentachlorophenol-based preservatives - an airborne contaminant that can affect cork and barrels, but also filtration mediums, even glass bottles. Like TCA, it causes musty aromas and flavours, but can go undetected at much higher levels.

pests & diseases . . . Too many to list here, but they're not kidding about good wine starting out in the vineyard and being coaxed to glory by one or other recipe in the cellar - poor grapes make for mediocre wine, at best.

ripeness . . . The level of grape maturity - ranging from under-ripe to optimal to completely dried-out - that spans different levels of sugar concentration and acidity. (Unripe grapes exhibit excessive malic acid).

sorbic acid . . . Sometimes added to wine as a preservative, instead of sulphur - detectable as a faint garlic-like smell when in excess.

sulphur . . . Sulphurous acid, sulphur dioxide (SO2) or sulphites are usually added to the grape juice or wine as a stabiliser or antioxidant (to delay or stop fermentation), or as preservative. Sulphur is also a sterilising agent for casks, barrels, etc, while in the vineyards it is often dusted or sprayed onto the leaves and fruit as a safeguard against many diseases, fungi and pests to which grapes are subject. The smell of over-sulphured wines can be acrid, pungent, and ranges from that of a recently struck match to bad eggs. (Sometimes too much sulphur can result in excessive acidity).

TCA . . . Trichloroanisole is a contaminant that taints wine with mouldy, musty and vegetal characteristics, and is generally produced through a chemical reaction between chlorine and wood or cork. It stems from chlorine-based disinfectants used in the preparation process of natural cork stoppers, as well as barrels and cardboard packaging materials.

volatile acidity (VA) . . . Organic acids (particularly acetic acid) and related substances (such as ethyl acetate) in excessive amounts can impart a vinegary or nail polish-remover (acetone) smell to a wine. Low concentrations can enhance the aroma and complexity of a wine, whereas high VA is indicative of unstable wine (sometimes attributed to poor hygiene in the winery).

DOWN TO THE WINEMAKERS

balance . . . Subjective to a point, but when they get it wrong and the components of a wine are badly out of harmony, you'll know it when you try it.

cheats . . . Whereas most make wine by the book, a few lean on additives, usually artificial flavourants, to overcome a wine's inherent shortcomings.

cold stabilisation . . . A clarification technique whereby the wine's temperature is lowered to the point at which tartrates and other insoluble solids separate out of the wine

control . . . Good winemakers leave nothing to chance; advancements in technology and improvements in equipment are a godsend to those who used to sleep in their cellars to ensure nothing happened without their say-so. Wine is a "living" thing - risky if you let it run wild.

fining & filtering . . . Or not! Removing yeast cells and other particles might be good for appearance and stability, but the procedures involved can alter a wine's characteristics - which is why some opt for a less processed route, despite what might happen after bottling (e.g. secondary fermentation, bacterial spoilage, sediment, crystals).

malolactic fermentation . . . Occurs after alcoholic fermentation: a second fermentation whereby malic acid is converted into softer lactic acid. It adds complexity to the wine and reduces the risk of "malo" taking place later in the bottle.

reductive . . . Reductive winemaking is optional and occurs partly in an oxygen-free environment, sometimes involving the addition of sulphur dioxide as an anti-oxidant. The rewards involve particular characteristics more difficult to achieve otherwise, but the off-putting odours evident in over-reduced wines make things tricky.

shortcuts . . . For example: the alternatives to using barrels to impart oak characteristics or promote longevity include planks of wood (staves), chips, even shavings - they're legal, but there's a reason why wine producers don't shout about such things on their labels!