glossary of technical terms

A labour intensive process to be sure, but slowly this will evolve into multiple pages - otherwise it will load much too slowly!!! So, starting with A . . .


Acetic Acid Bacteria.
A bacteria activated in the presence of oxygen which is often responsible for spoiling wine by oxidising the ethanol (alcohol), producing volatile acetic acid (ethanoic acid) and ethyl acetate (ethyl ethanoate). Improperly stored (empty) barrels are a common source of the bacteria, mouldy grapes can also be a 'good' source. Outside the wine world, it is exactly what is needed to produce wine vinegar.

Acids and Acidity.
When in balance you will only really note the presence of acid in a wine by the mouth-watering effect the wine has once you swallow. If the acidity is too high, you might find the wine becoming too tart or sour, whereas if it's too low the wine can seem, for want of a better word, 'flabby' or cloying. Acid is also the perfect foil for sugar. A wine can be incredibly sweet, but given enough acidity to balance the sugar and everything is just fine. As a grape ripens, the level of acidity reduces. Acidity is described as the concentration of acid in the wine or must. When measured in terms of 'total acidity' the higher the number, the higher the acidity, when measured in terms of pH, the higher the number the lower the acidity! Prior to any malolactic fermentation, the acids are typically acetic, malic and tartaric acids. If a malolactic fermentation takes place, much of the malic acid is converted to lactic acid. If a wine is low in acidity, tartaric acid is the addition of choice to 'try' bring more balance to the wine.

Acid Adjustment.
If the must is low in acidity, this can be adjusted before fermentation. In the finished wine, added acid is usually more noticeable if done post-fermentation, hence, these adjustments are normally done first. In high temperature regions the acidity is often lower than required and tartaric acid is typically used to compensate. If acidity is too high - often associated with (overly) cool climates - then adjustment is normally done after the fermentation. The advantage of adjusting after fermentation is that you know exactly how much 'low acidity wine', calcium carbonate or or potassium carbonate to add. Adjusting before the fermentation is usually a 'best guess' of what will be required.

Aftertaste.
Often referred to as the 'finish', this is the sensation of 'still tasting' the wine (sometimes long) after swallowing. This can be measured in seconds, or even minutes. The longer the time, reputedly the higher the wine's quality. If you think you need a scale try a French one which ascribes 1 'caudalie' to each second of length - so 20 seconds is 20 caudalie - I'm not sure why 'seconds' wasn't good enough(!) I have seen this in the translation from French of some tasting notes - but not very often.

Alcohol.
I suppose I should mention alcohol. Nature is a funny thing; it seems that 'someone' decidied that primary alcohols with and odd number of carbons should be very bad for you; methanol, propanol, pentanol etc., whereas, those with an even number of carbons; ethanol, butanol etc., should be less so. Of course, in high enough concentration all alcohols are toxic, but contrast methanol which destroys the optic nerve and sends you blind with ethanol that is the basis of a multi-billion dollar beverage industry - and the difference? - two carbons for ethanol and only one for methanol!

Anthocyanins.
RM Willstätter received the Nobel prize for chemistry in 1915 for his work on plant pigments. He discovered that fruit and flowers that have red, blue or purple colours contain pigment molecules based on cyanidin (right). When sugars attach to the points on the molecule (marked in red) the molecule is now called an anthocyanin. Higher sugar contents increase the solubility and stability of anthocyanins in water. Anthocyanins are divided into five classes depending on their structure: cyanins, delphinins, malvins, peonins and petunins - did you spot the name of your favourite flower? - this is where their colour comes from, the proportions of each anthocyanin will depend on the grape variety. Interestingly if the anthocyanin has mainly hydroxyl (-OH) substituents at the points marked in blue, the colour is shifted towards blue, whereas if the substituents are methoxylated (-OCH3) the colour is more red. Malvin is the most red of these compounds and is therefore responsible for most of the red colour in a young wine. The anthocyanins complex with sugars in the wine which helps to 'fix' the colour, it is only with aging that the anthocyanin complexes start to diss-associate and start to join up with tannins to form polymers - this causes both a gradual reduction in the intensity of the colour and also a reduction in the dissolved tannin.

Autolysis of Bacteria and Yeast.
Autolysis is the destruction of a cell after its death by the action of its own enzymes breaking down its structure. Autolysis can involve both bacteria strains and yeasts. Yeasts are micro-organisms responsible for the onset of fermentation, typically of the family Saccharomyces.
Because of the low pH and the increase in alcohol content the yeasts die. The dead yeasts in the wine barrel are called the 'lees', these dead cells can facilitate the production of lactic acid bacteria (lactobacillus brevis) which in tern promotes growth of Oenococcus Oeni which is involved in the malolactic fermentation.
It is believed that cell autolysis of Oenococcus Oeni has a primary role in the development of post-fermentative flavour changes. Looking at the photos to the right you can see the effect of autolysis breaking down lactic acid bacteria.

C. ZAMBONELLI et al.: Sensorial Characteristics of Fermented Foods, Food Technol. Biotechnol. 40 (4) 347–351 (2002)


Barrel.
The traditional wooden container used to age (and sometimes ferment) wine. For an excellent reference on barrel cooperage covering: History, Wood, Used, Quality, Evolution, Structure, Fabrication, Maturation and Conservation take a look here

(In) Barrel Fermentation.
Usually associated with white wine grapes, barrel fermentation is basically the conversion of grape juice into wine by yeast in oak barrels i.e. the primary alcoholic fermentation, though the secondary malolactic fermentation will likely also follow-on in the barrel. Despite barrel fermentation being more expensive and less controllable than an equivalent fermentation in stainless-steel tanks, it is believed to give the wine richness and slightly creamy flavours plus vanilla and coconut. Other oak derived characteristics such as improved aging capabilities come by following this route. On the downside, this technique contributes to a loss of some fruit flavour, plus, cool rooms and lower volumes (in barrel compared to tanks) are the basic form of temperature control!


Malolactic Fermentation.
After the alcoholic fermentation the wine has a mixture of volatile (mainly acetic) acids and non-volatile acids, mainly tartaric and malic acids. Malolactic fermentation is the action of bacteria and yeast strains on the malic acid, converting it to lactic acid. Because malic acid has two acid groups and lactic acid has only one, the malolactic fermentation results in a lowering of acidity (higher pH) - the acid group is lost as carbon dioxide. It is generally accepted that for 'high-quality' wines the 'malo' (as this fermentation is often called) is a good thing as it replaces the sometimes 'rough' malic acid with the smoother lactic, and produces a further layer of complexity. It is typically responsible for the buttery taste in chardonnay wines.

Must.
The must is simply the mixture of juice or wine plus the crushed grapes and grape skins, pips and stems, prior to removal of the 'solid' material.



Phenolics and Pinot Noir.
Pinot Noir has a very low phenolic content relative to other red grapes. These phenolics develop in the grapes, pips, skins and stems by the effect of UV light, hence, phenolic maturity is as much related to the availability of sunlight as temperature during the growing season. The phenolic (substituted hydrocarbon rings) compounds are principally anthocyanins and tannins. Additional phenolic compounds in wine come from the oak used during maturation.


Tannins.
Literally a range of compounds with the ability to tan leather (precipitate proteins!) they are a complex group of phenolic (aromatic) compounds which can be split into two groups; the 'simple' structures of non-flavanoids which can have their origin in either the grape material, yeast or oak, and the more 'complex' flavanoids which come only from grapes/stems. The anthocyanins from above are classed as flavanoids. In addition to helping to fix the colour with the anthocyanins, the tannins provide the characteristic dry, astringent mouthfeel in red wines and also act as antioxidants.