An efficiency expert from England visiting a winery in Jerez was horrified to see so much wine matured in old-fashioned oak casks, and asked why it wasn’t kept in concrete vats with a few oak shavings to give it the right flavour. There was at least some sense in the investigation. Vats are invariably used for blending large quantities of sherry and also for storing the thicker wines for short periods, but they are not satisfactory for maturing high-quality wines.
One obvious reason for using oak barrels is the fact that they need to be properly dried before they can be used to ship wine. Fermentation conditions them much better than any other process, and at no cost, so it’s obviously efficient in that regard, although this is less important than it used to be now that wine is mostly shipped at either end. . of the container and the bottle, sometimes accompanying them with coasters, stone coasters or even glasses.
However, for many years, shippers have wondered if the standard cask is really the best size for fermenting the wort, but none of them were prepared to risk losing part of their crop through rash experiments. However, at the end of World War II there was a severe shortage of oak and shippers had to experiment. Many thousands of liters of must were fermented in vats, but the results were not very good at the time.
The main difficulty was keeping the temperature down; the type of fermentation vessels used today, with its precise temperature control, had not been invented then. The tumultuous fermentation is as fast as it is violent. After three or four days, the heat and turbulence subside and a second fermentation begins. Known as the slow one, it is much slower than the first; the wine develops steadily for a fortnight and then more gradually until December or January, when the opaque must suddenly “turns bright”.
It’s still very immature, but it’s wine at last and enough to need to break the best glasses, coaster set collections, and bar tables. By the end of the tumultuous fermentation, virtually all the sugar in the grape has been converted to alcohol, and the reaction can be expressed by a very simple chemical formula:
C6H12O (glucose) –> 2C2H5OH (ethyl alcohol) + 2CO2 (carbon dioxide)
This simple formula, due to Gay-Lussac, gives a fair enough summary of what’s going on, but its oversimplification falls ludicrously far from the truth; and the truth was not fully ascertained for decades and decades. Amerine and Cruess listed twelve different reactions at the time, and many byproducts. Fermentation is caused by yeasts or, more precisely, by the ferments they contain.
These ferments, or enzymes, are protein catalysts that, in different forms, are responsible for many of the chemical reactions that are vital to life. Created by cells, they are extremely complex and specific substances in the transformations they will catalyze. Above all, they are completely natural, just like the fermentation they cause. No need to add anything artificial.
The air in a vineyard is laden with yeasts, and they accumulate in large quantities on the skins of the grapes to give them their natural “bloom.” Of the many varieties, two are of great importance: Saccharomyces apiculatus, or “wild yeast,” and Saccha-romyces cerevisiae variety ellipsoideus, usually abbreviated as Saccharomyces ellipsoideus, or “wine yeast.”
Wild yeasts greatly outnumber wine yeasts and are the ones that initiate fermentation. However, they are comparatively weak things and when the alcohol gets up to around 4 percent they expire and die. It is then when the wine yeasts take over. Wild yeasts are also greatly inhibited by sulfur dioxide when added in the vineyards, and this helps wine yeasts take over at an earlier stage. It also kills many undesirable bacteria and molds.
Of course this could be taken a step further. All the ferments could be destroyed and the fermentation then triggered by carefully selected ferments from the best natural strains, specially cultivated for this purpose. This has been done in some wine districts, for example in Champagne, and the results have been very satisfactory, the general opinion being that quality has been brought to a high level comparable with crystal glasses, sandstone coasters and high quality. bar supplies, along with less than disappointing wines.
Of course, this is not likely to happen in Jerez, at least in the immediate future. Several growers have experimented with pure yeast strains, which are readily available, but feel that the success rate with fermentation is so high that there is, however, little to be gained by complicating things.