The fermentation process is such a complicated biochemical process it would put Bill Nye The Science Guy to sleep. At least that’s what it’s cooked up to be from anything I’ve read, but it really is simple and I’m about to prove it.
The fermentation process involves three simple phases. The success of these phases depends on three factors, yeast, wort and temperature.
The initial stage is where the yeast starts to reproduce. The wort must have enough nutrients, and enough oxygen for the yeast to do so. The temperature must be ideal as well. If you pitch the yeast when the wort is too cold, then the yeast may go dormant and you won’t get any action. If the temperature is too high, then the yeast will go into a nympho like reproduction stage and will ferment too fast. This wouldn’t be a bad thing, but it creates off flavors which you probably don’t want.
This is the reason why you need to aerate your wort prior to pitching your yeast, and why you need to plan on how you will cool your wort so you can pitch your yeast at the ideal temperature.
What you may not know or even care to pay attention to is what type of yeast to use…
The amount of yeast or the type will depend on the type of beer you are brewing. You must have an idea of what the Original gravity will be in order to decide which and how much yeast to use.
See, during the first stage, the yeast uses the oxygen to reproduce. Once the oxygen is depleted, the yeast turns to sugars to reproduce by turning the sugars into alcohol. That’s when the actual fermentation begins. If you notice, the Original Gravity is higher than the Final Gravity. The reason for that is because as the yeast eats up the sugars it reduces the Gravity. This process is called attenuation. Every yeast packet has it’s expected attenuation levels. This is what you’ll use to plan for what and how much yeast to use.
You know fermentation is going on when Krausen starts to form and Gravity starts to drop.
That’s pretty much it. Simple enough?
Now there is one last stage that almost no one talks about, but it’s important to learn about. Once the fermentation is done the yeast will clean up and go through a conditioning phase. The Krausen and the alcohol produced during fermentation is very bitter. During the conditioning phase, the yeast turns the bitter flavors to a more taste bud friendly ones. This is why many brewers rack their beers and hold them on a secondary fermentation carboy.
So now you know why you need to aerate the wort, and why the temperature needs to be ideal. You also know why the airlock is not the absolute indication of fermentation, but rather the drop in Gravity that tells you when fermentation is done. Sometimes you’ll see airlock activity cease on day 6-8, but the beer will continue to ferment for a few more days.
You also know that in order to use the right amount of yeast, you must have an idea of what the Original Gravity will be and what you are looking to achieve as a Final Gravity reading.
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