Winemaker Blog – When to Harvest?


Marquette (red wine) Grapes

HARVEST PARAMETERS. We have lots of grapes schedule to arrive this weekend at Train Wreck Winery. We will be harvesting our own Marquette, and we will be getting Frontenac and Frontenac Gris grapes from several growers.

How do we know when the grapes are ready to harvest? Science and experience. In a perfect world, there would arrive a moment when the sugar and acids were in just the right amounts. That seldom happens. So we pull sample clusters from the vineyard, trying to get a representative mix of clusters. Clusters that are exposed to the sun will ripen faster than those that may be shaded.

We press the juice out of this sample, and test for pH, sugar %(called “brix”) and sometimes other things such as titratable acidity(TA) or yeast assimilable nitrogen (YAN). Because of variablilities of rain, sun and growing degree days, the numbers we measure in the lab are seldom exactly what we are aiming for. And even though our lab tests might dictate waiting, we may see degradation in the quality of the grapes in the vineyard, or maybe we have to pick this weekend because next week is the big game and nobody will want to help pick. So we pick when the science, our experience, and our gut tells us the time is right.


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