Cottonwood Part 4.
More excerpts from "Diary of an Unknown Vintner"...
…Camp Verde, near Cottonwood, Arizona…
Temperature and Brix of a vat of crushed red grapes showed how the fermentation is going. Daily readings showed, in the normal course of a fermentation, the Brix drops from about twenty-four to zero when all (or more accurately most of) the sugar has been converted to ethyl alcohol. Twenty-four Brix in grape sugar, if all goes well during fermentation, became about fourteen percent alcohol in the final wine. This was the upper limit for most wine grape fermentations for several reasons.
First, most grape varietals rose in sugar during late pre-harvest maturity, to twenty-four Brix. Further, wine yeast cannot tolerate much over fourteen percent ethanol to survive. To get a higher alcohol, the trick was to add brandy, about eighty-five percent alcohol, to wine such as port.
If the alcohol went higher than fourteen percent alcohol by volume (ABV), the tax on the wine tripled. Thus, the numbers were important.
There were all sorts of vintner tricks to accelerate or retard fermentation rates. A winemaker may desire a faster or slower rate, depending on his goal or objective for the wine in question.
Likewise, sugar was never added to wine to sweeten it.
The path to a sweet wine was to shut down the yeast before they consumed all the grape sugar available. Since this was sugar left over, it was referred to as residual sugar or RS.
The laboratory work of the novice winemaker/intern was focused on providing the head winemaker accurate and timely numbers by which he could make informed decisions about how the ferments were developing and which, if any, corrective measures were indicated.
The involved things like which yeast strain to use, whether yeast needed extra sources of food, vitamins or nitrogen, in addition to what was available in the grapes themselves. Unhappy yeast emit the rotten egg smell of hydrogen disulfide and the must began to take on the aroma of vegetable soup, not wine. It was best to be sure the yeast were extremely happy and healthy for the best results in finished wine. If the ferment was too cold, the reaction might have sputtered our prematurely before an appropriate level of alcohol is achieved, resulting in what is called a stuck fermentation, and is problematic to restart. If too hot, some of the desirable aromatics may vaporize and be lost, detracting from the characteristic nose of the finished wine.
Temperature and alcohol in fermentations also had an effect on how well the grape skin color is extracted into the liquid portion of the ferment.
If fermenting juice in a red ferment was removed early, before all the color came out of the skins, the result is called a rose wine. Such rose wine can be made from any red grape, although most winemakers often had a favorite varietal.
Where wine chemistry data became mission-critical, was at the conclusion of the fermentation. If sugar (or malic acid) was left on the table, bottled wine was more susceptible to spoilage in shelved bottles. So, the laboratory values for glucose/fructose, and malic acid informed the winemaker at what point he ought to halt the ferment by adding a small amount of sulfur dioxide.
That was the killer: if the laboratory data were inaccurate, vats of three thousand gallons wine might be ruined. That is huge sums of money lost.
So, the lab intern’s role was to extract a pipet-full of wine from each tank every day for testing, then to enter data into online spreadsheets accessible remotely to the winemaker at any time of day or night. Curiously, the pipet designed to sample wine was called a wine thief.
The exercise of rolling around the cellar each day was not unlike a doctor making hospital “rounds” daily to keep track of his critical patients on a regular basis.
After sampling, the chemistry was a little more involved and perhaps best left for another session…