A little about fermentation

I spoke a bit with Judy from the Keystone Homebrew Supply and she recommended that I leave the ESB in the fermenter for two weeks, and bottle-condition for a minimum of two more weeks.

That surprised me, since with my first batch the pale ale recipe suggested one week in the fermenter and 3-4 weeks of bottle conditioning. So I checked Palmer, and I'm going to go with two weeks in the fermenter this time. In fact, I recommend that anyone extract brewing for the first, second, or hundreth time who has questions on hows and whys, have a look at Palmer Section 1. Once I get around to all-grain brewing, I will likely recommend all the other sections as well.

Palmer's chapter on fermentation (linked above) gives a very clear description of the three phases of fermentation: To make clear the reasons for fermenting for at least two weeks rather than just one, I will summarize the phases briefly here:

1. Lagtime/Adaptive: In the first 12-24 hrs, yeast will multiply rapidly in an aerobic reaction (aerate your wort well! but only when it is cool!). 24hrs with no activity? Pitch new yeast.
   
2. Primary/Attenuative: Once the oxygen is used up, the yeast will anaerobically metabolize sugars to alcohol. This phase lasts 2-6 days for ales, and longer for lagers. In addition to making ethanol the yeast creates several byproducts including carbon dioxide (bubbling in the airlock), acetaldehyde, esters, amino acids, ketones, dimethyl sulfide, fusel alcohols (hangover material) as well as precipitate of wort protein, hop resins, and dead yeast.
   
3. Secondary/Conditioning: 1-2 weeks more. Now the yeast converts the remaining sugars and also metabolizes byproducts that could give off smells/flavors (e.g. acetaldehyde - green apple); or cause the beer to go stale quickly (diacetyl and pentanedione - buttery and honey flavors). Fusel alcohols are converted to esters (fruity flavors). Yeast flocculates out, and the beer clears. Time to bottle!

Note: One can choose to rack the wort to a secondary fermenter in the conditioning stage - away from the trub, the exudate in the bottom of the primary (full discussion in Palmer - I'm not doing this yet).

So bottling after only a week means missing out on all the benefits of the conditioning phase. However, do not to leave the wort in the primary fermenter more than three weeks at the outside because the yeast will undergo autolysis. This means the yeast cells themselves break down and release their innards into your beer, ruining it. Very potent rotten egg or burnt rubber smell when you open the fermenter.

I may look into secondary fermenters before I put in my IPA. Certainly the German Altbier kit I have requires it, so I could get some practice!