Thanks!
Now how do you know primary fermentation is done? From what I have heard, fermentation will stop for one of two reasons:
They ferment everything, run out of sugar, and starve or
they make so much alcohol, they end up basically poisoning themselves.
...Now how do you know primary fermentation is done?...
That’s where the hydrometer comes in. Starting at about day 7 (or 10, after the yeasty foam has settled down), take a hydrometer reading of the fermented wort. Use a sanitized turkey baster or wine thief to obtain a sample from the fermenter.
The hydrometer will give the specific gravity of the liquid. Correct the reading for the temperature of the wort (most hydrometers are calibrated to pure water at 60F (SG = 1.000) and have a calibration chart for different temperatures). Record the specific gravity. (This is where a digital thermometer and a brewing software program (like ProMash) come in handy).
When you see a constant SG reading over 2 or 3 days, then the primary fermentation has stabilized and you’re ready to bottle. The yeast cells have indeed digested as much of the sugar as they can and/or have created more alcohol than they can handle. They go dormant until more of the right type of sugar becomes available (such as during the conditioning phase).
(yes, that means that you’re drinking yeast poop!)
I’ve found that 2 weeks works just fine (15 years homebrewing experience) to complete the primary fermentation. Since I usually brew on a weekend, I don’t have to sweat bottling on a weekday evening. All part of the “relax, don’t worry” part of this avocation.
A few practice runs with the hydrometer and plain sugar water can help with developing a good procedure for the limitations of your work area and an understanding of how to read the meniscus and converting to the true SG.
Recommended reference: “The Complete Joy of Homebrewing” by Charlie Papazian. I read mine until it was about dog-eared before I started brewing, to help visualize the steps in the process.