Rehydrating and Tempering Yeast

On Tuesday, a full 3 days after putting our juice in the refrigerator to cold settle, we started to rehydrate our QA 23 yeast. I looked at various sources to figure out how much yeast I needed to add to the juice. I went back to my notes from the U.C. Davis Online course that I took and I also found an excellent online article from MoreWine! Inc called Guide to White Wine Making.
Rehydrating Yeast

• Rehydration procedures are important to yeast viability.
• This procedure took approximately 45 minutes.
• I used Poland Spring water that was warmed to 100 degrees Fahrenheit, as recommended.
  It is recommended not to use tap water or juice that may contain fungicides or preservatives which will significantly decrease yeast viability, for this first step of yeast rehydration.
• The recommended reconstitution and inoculation procedure calls for 25 grams of dried yeast per 100 liters (0.25g/L) of must or juice to achieve approximately 5 x 10⁶ viable yeast cells per milliliter of solution and a peak cell density of 1.2 to 1.5 x 10⁸ cells/mL. This inoculation density helps ensure a rapid onset of fermentation and dominance over indigenous yeast.
  For our purposes, I scaled this to our volume of 5 gallons or 18.9L and calculated the addition to be 4.725 grams of yeast. Our yeast, QA 23 comes in 5 g packets so I used one packet.
• We rehydrated the dried yeast by slowly sprinkling into 10 to 20 times its own weight (100 – 200g yeast/L), in our case, 50 mL of clean Poland Spring water pre-heated to between 38(100°F) to 42°C (108°F). The recommended procedure is that gentle stirring may be used to improve yeast wetting and dispersal to avoid clumping. Vigorous stirring or mixing should be avoided as it may damage or lyse rehydrating yeast cell walls. We gently swirled the Pyrex 2 cup measuring cup that we used to rehydrate our yeast.
  

Tempering Yeast

• We let the yeast bloom for approximately 15 minutes while we waited for our juice to warm up to 60 degrees.
• Our next step was to lower the temperature of our rehydrating yeast from 100 ^oF in incremental steps by adding in our juice. We took 25 mL of juice and added it in 5 mL aliquots every minute and then let the mixture acclimate for 15 minutes. This brought the temperature down from 100 ^oF to approximately 85 ^oF. We waited 15 minutes.
• We repeated the above step, taking another 25 mL of juice and added it in 5 mL aliquots every minute and then let the mixture acclimate for 15 minutes. We were able to bring the yeast mixture down to 70 ^oF.

At the end of the rehydration, our yeast mixture looked like this:

We were ready to pitch the yeast into our cleaned fermentation vessels, which are stainless steel beer kegs that my husband procured for the fermentation. After moving the juice from the Poland Spring jug into the kegs, we moved the kegs into our refrigerator which my husband converted into a temperature controlled (at 62 ^oF) environment, to ensure a slow and long fermentation.

1. VID253, The Regents of the University of California 2007, Lesson 6 – Page 8 of 25.
2. Scott Labs Yeast Rehydration Protocol
3. MoreWine! Inc, Guide to White Wine Making