I recently recorded a spot for America’s Test Kitchen Radio on sweet wines. Frankly, it didn’t feel that successful but as is often the case the effort wasn’t without its compensations. It came in the form of a new idea – and possibly some insight – about how sweet wines may have come about.
Nothing scientific or historical here, I’m afraid – most of what follows is strictly conjectural.
I’ve mentioned before that the evolutionary biologists tell us that our distant hominin ancestors came down from the trees already addicted to the sweet taste of ripe fruit. Grapes, having the highest load of sugars of any fruit were thus instantly to us attractive wherever we found them.
What a thrill when we learned that fruit sugars would spontaneously ferment, giving birth – under the right conditions — to that marvelous, mood-altering substance: alcohol. Hurrah!
Now imagine the stunning disappointment which must have followed with shocking immediacy when we realized that that lovely alcohol came at a high cost. All that dreamy sweet fruit that attracted us to grapes in the first place was used up in making the alcohol. Boo! Hiss!
My guess is that a yearning to have our fructose and alcohol too is what drove the R&D necessary to create a stable, palatable sweet wine. In the end it really must have been a matter of domesticating yeasts in the same way we would — sooner or later — later domesticate larger animals.
Keeping a herd of goats or sheep for the meat and milk they can provide required pastoral peoples to think in terms of sharing, rather than just appropriating. It’s clear that sheep need milk to raise their young, and that since a proportion of these young need to be preserved to breeding age in order to perpetuate the herd animals cannot be slaughtered prematurely. Once the future of the herd is assured, shepherds can safely take the surplus meat and milk for themselves.
Early winemakers likely applied essentially the same principle to create sweet, alcoholic beverages. They did this by inventing techniques for generating a surplus of sugars prior to fermentation, an amount over and above what was required to satisfy the voracious appetite of the yeasts.
This strategy could succeed because while fructose and glucose-loving yeasts live and reproduce on sugar, they have a very limited tolerance for alcohol. As yeasts gorge themselves on sugars in the fermenting tank, alcohol levels rise to concentrations that prove lethal for the microscopic critters. When yeasts die, fermentation stops. Whatever sugar has not been converted to alcohol and CO2 remains in the wine – the surplus that provides the sweetness.
Ancient techniques to raise sugar levels to levels that woulid provide a surplus involved simple methods of concentration: allowing grapes to hang on the vine beyond normal ripeness (late harvest), twisting the stems on ripe bunches while still on the vine so the berries dessicate, or harvesting at normal ripeness and spreading the grapes out on mats to dry (the passito technique; there are many variations). All are still in use.
After the invention of distillation it became possible to arrest fermentation at any point by the addition of yeast-lethal amounts of neutral grape spirits. Fortification, as this is known, is standard practice in Port and Sherry production. Once refrigerated tanks came into use, fermentation could be stopped simply by dropping the temperature.
It all makes me wonder whether we waste our time arguing over whether man’s first successful domestication was of the dog, goat, or barley. It may have been the lowly yeast.