Rehydrating Yeast
You don’t need to follow these directions to get a ferment to work, but you will be more likely to get a ferment that produces better wine flavors and minimal H2S if your give the yeast a proper start in life.
Equipment you will need
- Dry yeast of appropriate type
- Container (jar), the wider the better (a larger surface makes for easier rehydration of yeast)
- Water
- Thermometer
- Microwave or other means of heating water
- Go-Ferm (a balanced yeast nutrient—highly recommended) or Super Food
- Quantity of cold juice from must
Steps
- Determine the quantity of yeast you will need. The minimum is 5 grams per 20L of juice. Use double this dosage for low temperature ferments, high sugar musts, or musts where you have mold or possible VA problems. Yeast is cheap. Don’t skimp.
- Warm a quantity of water at least ten time the weight of yeast you are using. There is no harm in using 20 times the weight. You can use some diluted juice instead of water, but make sure that it is no more than 7º Brix.
- Get the temperature to 35-38ºC. Don’t guess. Use a thermometer. Temperatures below 35º do not work as well. Temperature above 40º can damage the yeast. Digital meat thermometers with a probe work very well.
- Add 1.0-1.2 grams of Go-Ferm for each gram of yeast you are intending to use. Stir gently to dissolve. Recheck to see temperature is 35-38º.
- Sprinkle yeast gently on top of surface. Do not stir. Let the yeast settle gently to the bottom. If necessary, shake the container gently to increase settling. Stirring will usually just produce lumps.
- After 15 minutes you should be seeing some yeast activity. Stir gently to dissipate yeast.
- Start adding cold juice to bring the temperature down. Do this gradually. You don’t want to shock the yeast but it is very important to have the temperature below 35ºC at the 20 minute mark and below 30ºC at the 30 minute mark.
- Continue to bring down temperature until it is no more than 10ºC above that of the must to which it is going to be added. No more than few degrees difference is better. There is no big no hurry to get the yeast into the must once the temperature is below 30º and the yeast is acting in a solution which contain some juice.
- Add to the must by pouring gently into a small pool on the surface. This will allow the yeast to acclimatize to the temperature and higher sugar of the must. Don’t stir in. The yeast will spread well enough on its own.
Yeast action should be evident in your must in about 24 hours, provided the temperature of the must is about 20º. Yeasts first expand their population before they start converting sugar to alcohol and producing much CO2.
For further reading:
Loubser, Piet (2003). “Nutrition during rehydration—a new approach to yeast nutrition,” Wynboer, January 2003. This is a discussion of why Go-Ferm is important. It is available at http://www.wynboer.co.za/recentarticles/0103rehydration.php3