Winemakers generally use inoculated off-the-shelf yeast strains, not least because they are reliable fermenters. The alternative, wild yeasts, are more temperamental. These are found in the vineyard and winery, and they can give a distinctive, bombastic, highly sought-after gout to terroir. On the other hand, the ferment can stick, and they can be a bit funky. Another strange indigenous yeast is Brettanomyces (Brett in wine-speak), a yeast found in wineries which can impart a farmyard character in wine. A little of this can be interpreted as complexity, but if it`s overly pongy I would take it for the fault it is. Undoubtedly yeasts most important role in winemaking is converting grape sugars into alcohol, but it`s their use in contributing to wine`s aroma, flavour and texture I find most intriguing, not least because it gives rise to some of my favourite aromas. These are brioche, fresh- bread, pastry and biscuit, but also, potentially, nuttiness and acacia. These characters are most noticeable in wines which have had extended contact with the yeast, whether in tank, cask or bottle (the latter, in the case of Champagne, for example). The yeast cells gradually break down, a process known as yeast autolysis, releasing attractive esters and glycerol into the wine, which adds complexity, richness and texture. It`s this which gives us the term “leesy” or Sur Lie denoting the yeasty characters in the wine. Lees refers to the sediment, including trillions of dead yeast cells, deposited during and following a wine`s fermentation. A classic example is Muscadet de Sevre et Maine `Sur Lie` from the Melon de Bourgogne grape, fresh, lean, bone dry and “leesy” with an affinity to mussels and oysters. The effect, if not the flavour, is not unlike the pearly mineral match cool-climate Chablis has with shell fish. There again, from Cote d`Or in burgundy, I know of Chardonnays benefiting from lees aging and a process called bâttonage – stirring of the lees in barrel – which ensures normal autolysis while developing a creamy palate. Such wines are suited to seafood with rich sauces.