Fermentation theory, yeast particulars, the who what and when why...

So, my sickness is growing...I lay in bed sleepless, wondering about yeast and fermentation times and all this whooditty.

Sick, just sick.

In order to quiet the sick sadist beer sloth, muttering in my pretty little head...I'd like to get some direction out of you crusty clowns.


Lets for example take this smidgeon of brew conflict I have rattling around like a bb in my tin can head.

I've seen it posted as of late that this s - 04 yeast is a "fast" yeast. Purportedly most activity halting within 72 or some odd hours. Fine. Then I stumble upon a recipe for a Founder's Breakfast stout clone. The recipe for this particular brewlicious godly nectar of fantasticishnessisosity, desires 2 weeks in the primary AND....yes AND...calls for this Safale S-04 speed demon of a yeast. AND! 2 packages no less!

NOW! I understand that the original gravity being fairly high and there's seemingly quite a bit of goodness for the yeast to chew through. But, my questions is...

What determines a proper primary fermentation duration? Style, OG, Activity, many things combined, yeast protests, semi annual elections?

If lets say the airlock stops farting at say 8 days on this particular recipe...is the extra 6 days for good measure, personal preference, sweet torture for the masochisticly impatient?

So, in short, I need input, information, data...sources, theories, postulations.

Got a good book to recommend?

A web based source?

Should I got back to high school chemistry not so....err....artificially hungry, shall we say?

Please...I need sleep. Help.

You ask a great many things and in wonderful ways but the only thing I can think to say is use your hydrometer. If you take a gravity reading over the course of like 4 days and it's still the same then you would be able to assume that the majority of fermentation is over. Now people leave it in primary for longer than that to let the yeast clean up all the nastiness like diacetyl and whathaveyou. Yeast are smart little buggers and if you give them time, the proper conditions and love them, then they will love you back.

Yes, after primary fermentation is done it's generally a good idea to let the beer sit so the yeast can do some more work and the flavors can meld. Doesn't matter what kind of beer you make; letting it sit after fermenting is almost always a good idea (though different styles do need less time - very roughly, higher OG beers need more conditioning time and lower OG beers less).

StumpyJohnson said:

What determines a proper primary fermentation duration? Style, OG, Activity, many things combined, yeast protests, semi annual elections?

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Style = not so much. OG = yes; the more sugars the yeast have to chew through, the longer it will take them. Activity = yes; the more yeasties there are, the quicker they'll eat. Temperature also makes a big difference (lower fermenting temps = slower ferments).

Got a good book to recommend?

A web based source?

Click to expand...

Here's a good place to start:
http://www.howtobrew.com/

Good luck!

Also, 2 weeks in primary may not mean 2 weeks of fermentation. Perhaps this person doesn't rack into a secondary fermenter and they are just telling you that but in a really confusing way.

Not to mention that while fermentation itself may be done within 72 hours (depending on OG, nutrient levels, yeast activity, oxygen, etc.), the beer is not "done". The yeast hang out for a few more days to clean up and all of that nice stuff, so while the sugar consumption may be over, it's not finished.