A couple of weeks ago I touched briefly on wild fermentation, but I've recently come across a wine that prompts me to explore the subject in a little more depth. The background to the story is this; the bloom that you will find on the skins of grapes growing on the vines, is yeast. Yeasts are fungi; not ground-living like the mushrooms you pick in fields, but fungi none the less. Their spores are air-borne and they propagate by means of the wind. The yeasts that we use for bread-making and fermenting beers and wines are all descendants of these wild yeasts - carefully selected and refined over generations to better do their allotted tasks.

To begin at the beginning. If you leave bunches of grapes in a container, the grape juices will run out under their own weight and the yeasts that are present on the skins will digest the sugars in the juice and secrete a waste product that we know as alcohol. This is probably how early man discovered wine - and beer for that matter. Most of the wine-making yeasts are of the saccharomyces family, but other, less desirable yeasts such as acid forming ones, can often be found on grapes. These need to be destroyed by the wine-maker before introducing a cultured yeast. This means that using the naturally occurring yeasts can be a hit and miss affair, so it's now almost a universally adopted practice to use only cultured yeasts that have been genetically and specifically selected for making wine, beer or bread.

Not all naturally occurring fungi on grapes are used for fermentation. In some climactic conditions and with certain grape varieties - especially the Semillon - a fungus known as Botrytis cinerea settles on the grape skins. It's known in the Sauternes as the 'pourriture noble', or the noble rot. It's effect on the grapes is to shrivel them - so by leaving the grapes on the vine long after maturity, late into the Autumn and Winter, they eventually lose much of their water content. This concentrates the sugars, allowing the wine-makers of Sauternes to make a full-bodied wine with normal alcoholic strength, but with residual sugars remaining, giving us their inimitable dessert wines. This is also how many German auslese are made, as well as the Hungarian Tokay.

It takes a brave wine-maker to let nature take its course and let wild yeasts do the job of fermentation, yet that's precisely what Ed Flaherty has done. He's the wine-maker for the Chilean winery Errazuriz, and he's taken a portion of the Escultura estate Chardonnay production and allowed it to ferment with its natural yeasts.

Wine of the Week

Errazuriz Wild Ferment Chardonnay 1999

This is a wine with all the complexity, length and structure of the finest white Burgundies. The wild yeasts give the wine a velvety texture and produce a mixture of aromas, both floral and fruity. It's sealed with a synthetic cork, so there should be no 'off' flavours to contend with.
RRP. £12.99 Available Molloys, Redmonds, O'Briens, Berry Bros. and selected off-licenses.