The last home brews I’ve done I’ve used yeast starters. If someone happens upon this and don’t know the theory it goes like this: if you’re brewing you want to make sure that 1) your yeast is alive, before the brew day when it is usually too late; and 2) you want to make sure you use enough yeast for your particular brew. Here’s a run down on why I always do starters now, even though I haven’t actually failed any brew without it.
Yeast will go through 3 stages in the brew process.
- Adaption. This is on the day when you brew and have pitched the yeast into your wort. In this phase the yeast adopts to the new environment using primarily oxygen to multiply as needed. Usually this happens within the first 24 hours.
- Fermentation. This is when the yeast do it’s primary work: feeding on available sugars and producing carbon dioxide and alcohol. This may take anywhere from 1-7 days depending on the strength of the wort, the condition of the yeast, the temperature etc. But usually this will be done in about 4 days.
- Conditioning. Now when all easily available sugars have been gobbled up the yeast starts to sink to the bottom in the fermenter and will form a thick sludge at the bottom of “sleeping” yeast (which you can collect and use in subsequent brews if you like). There will still by yeast cell active in the wort but it will work slowly on diacetyls and and rests. The heavier the beer, the more important this phase is.
Making sure you pitch enough yeast will shorten the adoption time and make it easier for the fermentation. A yeast which is “rushed” (ie. if you pitch to little) may produce more diacetyls, fuesels and esters, all of which you may not want.
And to the point: I ferment in my apartment which usually have an ambient temperature of about 23C. This is in the very uppermost range of what most yeast families like, and they will produce more esters and fuesels they warmer it gets. Check the paragraph above: fuesels and esters… I can’t do very much about the temperature in my apartment – it’s controlled centrally – so therefore it makes sense for me to do a starter: every little count. Not to mention the the attenuation (how much of the sugar the yeast actually use) have been more effective with the starterts.
Oh, and I’m using this excellent little calculator to check the starter numbers: http://www.yeastcalc.com/