To determine how much yeast you need for 20 gallons of mash, we can use the recommended ratio of 2 to 4 grams of dried yeast per gallon. Since you have 20 gallons, we can multiply this ratio by 20 to get the total amount of yeast needed.
Using the lower end of the ratio, 2 grams per gallon, we would need 2 grams x 20 gallons = 40 grams of yeast.
On the higher end of the ratio, 4 grams per gallon, we would need 4 grams x 20 gallons = 80 grams of yeast.
So, for 20 gallons of mash, you will need between 40 grams and 80 grams of dried yeast. The exact amount you choose to use within this range will depend on your personal preference and the desired fermentation characteristics.
It's worth noting that the amount of yeast needed can also depend on the specific recipe and style of beer you are brewing. Some styles may require more yeast to achieve the desired flavors and fermentation characteristics. It's always a good idea to consult a recipe or brewing guide for more specific recommendations.
Additionally, it's important to ensure that you are using a high-quality yeast strain that is suitable for the style of beer you are brewing. Different yeast strains have different fermentation characteristics and can greatly impact the final flavor and aroma of your beer.
When it comes to fermentation, the formation of a foamy, rocky head of yeast called kraeusen is a good sign that fermentation is active and progressing as it should. This kraeusen typically forms within the first four hours of fermentation, although it can sometimes take up to 24 hours. If you don't see kraeusen forming immediately, don't worry, as long as fermentation eventually starts, it should be fine. Patience is key in the brewing process!
For 20 gallons of mash, you will need between 40 grams and 80 grams of dried yeast, depending on your personal preference and the specific recipe or style of beer you are brewing. The formation of kraeusen during fermentation is a positive sign, and it should typically occur within the first four hours, although it can sometimes take longer. Happy brewing!