Yeast Book (White & Zainasheff) Thoughts
Posted: Sun Feb 13, 2011 11:04 am
I finished reading JZ's Yeast book yesterday. It's well written, easily approachable, and I recommend it to brewers of any level. Properly handling yeast & fermentations is one of the best ways to improve your beer. This book does a good job of covering everything you need to know about factors that drive fermentation character (pitching rates, oxygen, temperature, etc.) as well as topics like yeast starters, harvesting yeast, and long term storage. It even has a lengthy discussion of proper laboratory practices if you want to be a bit more scientific.
One point caught my eye yesterday as I was reading the trouble-shooting section: "Overpitching yeast will never result in over attenuation." Moderate underpitching can cause the FG to come in a few points high (e.g. 1.012 instead of 1.010), but pitching too much yeast will never drive the FG of your beer below its limit of attenuation. Nor will over-oxygenation or fermenting too hot. These factors only control ester production & fusel alcohol levels. The authors state that the best mechanism to control attenuation is grist composition. (Mash duration & temp are second and third order effects.)
When I reflected for a minute on that statement, it made good logical sense, but I had always believed that the FG of your beer is a function of how much yeast you have. If underpitching, pitching too hot, fermenting too cold, and poor oxygenation can cause underattenuation (as many of us know), then I assumed that pitching too much yeast, over oxygenating, or fermenting too hot could result in overattenuation. Turns out that isn't true.
So, if you're like me and routinely get 80%+ attenuation levels, it's not b/c you're pitching too much yeast.
One point caught my eye yesterday as I was reading the trouble-shooting section: "Overpitching yeast will never result in over attenuation." Moderate underpitching can cause the FG to come in a few points high (e.g. 1.012 instead of 1.010), but pitching too much yeast will never drive the FG of your beer below its limit of attenuation. Nor will over-oxygenation or fermenting too hot. These factors only control ester production & fusel alcohol levels. The authors state that the best mechanism to control attenuation is grist composition. (Mash duration & temp are second and third order effects.)
When I reflected for a minute on that statement, it made good logical sense, but I had always believed that the FG of your beer is a function of how much yeast you have. If underpitching, pitching too hot, fermenting too cold, and poor oxygenation can cause underattenuation (as many of us know), then I assumed that pitching too much yeast, over oxygenating, or fermenting too hot could result in overattenuation. Turns out that isn't true.
So, if you're like me and routinely get 80%+ attenuation levels, it's not b/c you're pitching too much yeast.