Winemaker Blog – Fermentation and Stuff

Steve has been busy in the cellar and around the state over the past week. Here are his notes from this period. Enjoy!

FERMENTATION. On Friday Aug 29th we inspected the juice. Very little activity is present. This is due to the temp of the juice. Going from the freezer, thru the destemmer, and thru the press, the resulting juice was in the low 40’s. By Thursday it had raised to 52 degrees. Today it is 56 degrees, so the juice is still a little chilly for our yeast, for which the optimal temp is 59-65 degrees. We’re keeping the facility chilly (60 degrees) to encourage this slow warm up. We want a slow, cool fermentation to encourage the properties we want in the finished wine.

We now have Brianna, Edelweiss and St Pepin juice fermenting in the winery. We are monitoring the Brix in the wine to make sure the fermentation is going smoothly. Once about a third of the sugar has been converted to alcohol, we add nutrients to the fermenter. The product we use is Fermaid-K. This product provides yeast nutrients, particularly nitrogen, to the yeast cells to ensure they don’t stress from lack of essential foods. Other stressers include high alcohol and heat. We treat the latter by keeping the volumes low and the winery cool. As we’re shooting for an alcohol level of 11%, the fermentation should be complete before high alcohol becomes a problem.

Brianna grapes

Brianna grapes

This year many growers are reporting sour rot in their Brianna grapes. Unlike other fungi that we prevent by proactive means, sour rot occurs when grapes are damaged. The skin on grapes can be broken by any number of things: insects; hail; cracks caused by drought/too much rain; birds. Once the skin is compromised, sour rot sets in. At that point there is little to be done except to sort the clusters at harvest and get the grapes processed as quickly as possible. The main concern is the amount of Volatile Acidity (VA) in the juice/wine. VA is basically vinegar, and can cause flavor issues. There is a federal limit of 1.2 grams/liter of VA. So I sent juice samples off to the Iowa Grape and Wine Industry Institute for testing, and our VA is well within the limits.

Snuck away from a function at the Depot last night and added Fermaid-K to two tanks of Brianna. The sugar had reached about 2/3 its original amount. Fermentation additions have to be done at certain points of the process, and cannot be delayed.

Checking the ferms this morning for temperature and any off-odors that may have developed. We’re off to a wedding in the Quad Cities this evening, so won’t be able to check them again until noon on Saturday. I think we may be getting grapes in tomorrow, too.