Winemaker Blog – Starting the Ferment

The next step in the process is to put all that lovely juice into a tank and begin fermenting.  Here’s what we do:

WINE MAKING. We pumped all the juice into a single tank. We measured our pH (3.05), our sugar (15.5) and our free sulfites (0 ppm). I added sulfites to the grapes in the cooler for two reasons: to prevent wild yeast from starting fermentation; and to prevent oxidation (browning) of the juice. After processing there was 0 ppm(parts per million) free sulfite, so I added enough to have 50 ppm in the juice. 50 ppm is enough to inhibit wild yeast, but not our special wine yeast. I also added sugar to increase the Brix of the must to about 20%. We will want about 11% alcohol in this wine. A rough rule of thumb is that the final alcohol percent in the wine is 55% of the starting sugar level. So 20 X .55 is 11. After sugar addition, we let the juice settle overnight.

The frothy bubbles tell us the yeast is ready to "pitch" into the juice.

The frothy bubbles tell us the yeast is ready to “pitch” into the juice.

PITCHING THE YEAST. We started Thursday morning by making our yeast propogation. Starting with warm (100 degree) water, we first added a product called Go Ferm. This product contains nutrients and micro nutrients that help the yeast fully rehydrate and get off to a good start. We then add the wine yeast. The yeast we are using for this wine is called Aroma White, manufactured by the Enartis company. This yeast has the characteristics we’re looking for in making a young, aromatic wine fermented at low temperatures. After about 20 minutes the yeast prop begins to bubble as the yeast begin to reproduce. Over the next couple hours we introduced small amounts of the juice to acclimatize the yeast.

Meanwhile we verified our 20% sugar, and rechecked the free sulfites (SO2). Instead of 50, the result was 16ppm. This is because a large portion of the SO2 we added had become “bound” to other substances while performing it’s protective role. So we added SO2 again to achieve our desired 50ppm. We then pumped the juice to another tank, leaving as much sediment behind as possible. We then split the juice into two tanks, and pitched the yeast into each.

The reason for using two tanks is twofold: at peak fermentation the wine will develop a great deal of foam, and we need head space to prevent overflow; and heat is developed during fermentation, so the smaller amount in each tank will help the heat dissipate. Once the yeast is pitched we enter the “lag phase”. During this period the yeast are reproducing like teenagers. At some point the activity will become noticeable, as the yeast cells approach 10-12 million yeast cells per millileter. Then the lag phase will be over, and full fermentation occurs.

Cheers, Steve

Winemaker Blog – Processing

After pressing the grapes the by-product is a dry "must" - the grape skins and rice hulls.

After pressing the grapes the by-product is a dry “must” – the grape skins and rice hulls.

Processing the Grapes: After a couple days battling bearings and starter capacitors, I had the destemmer ready to go. Wednesday, August 27th, we processed our Brianna grapes. The grape clusters are manually shoveled into the destemmer hopper. This machine spins the berries off of the stems, and simultaneously breaks the berry skin. An internal pump moves this mash of skins, pulp and seeds(now called MUST) thru a hose to the vertical bladder press.

The press squeezes the juice from the must, which we then pump to a tank. Our grapes fall into what is known as “slip-skin” varieties. During processing the skins slide whole off the pulp. These skins can then form nearly impenetrable walls inside the press, preventing the juice from getting out. So we use rice hulls in the press. Rice hulls are the seed coating left after rice is processed, and dumping adequate amounts in the press with the must forms channels that the juice can use to escape. It allows us to increase the juice yield. A typical juice yield from a ton of grapes is 150 gallons. We got a yield of about 168 gallons per ton using the rice hulls.