Attenuation and Homebrewing

Why am I obsessing over my homebrew's attenuation? Because I have OCD. To refresh, attenuation is basically the amount of sugars converted into alcohol and carbon dioxide by the yeast (thank you, Wiki Brew). This number is given by a percentage. Here’s where it gets a little confusing: There is “real” attenuation and “apparent” attenuation. Why not just go by real? I have no idea. Why do beer brewers make this so difficult for me? I do know that by understanding what attenuation is, I can build a better beer, and that’s all that matters.

How does attenuation affect the character of beer? The yeast won’t eat up all the sugars during fermentation, so the amount of fermentable sugars left in the beer will affect the all-around “character” of the beer. Different styles have different amounts of fermentable sugars left when it’s at the drinking stage. This is where the hydrometer comes into play and where “real” versus “apparent” is found. The thing is, a hydrometer can’t measure the amount of ethanol in the beer, so the reading is off a little bit. The reading will show a lower sugar (extract) level than the “actual” beer has in it. That’s why this initial reading is called the “apparent” attenuation. If you want to know the “real” attenuation, you’d have to burn off the alcohol before using the hydrometer and use this formula: real extract = 0.1808 * original extract + 0.8192 * apparent extract. I prefer to use my beer app, though.

Here’s what I found most interesting about this whole thing: Different yeast strains have different attenuations. This is where getting crazy-awesome with your own personal made-up recipe can get fun. Lager yeast actually consumes all of the sugars, so there’s already a huge difference between ale and lager yeast right there. When the yeast drops to the bottom of the bucket (flocculation) or sit on the surface of the beer, it stops having much contact with the sugars. A funeral for the yeast cells is then needed. What happens when the yeast “dies?” There are still fermentable sugars left in the beer, which is part of that whole character thing. The rule usually goes:

Less flocculation = more attenuation

Closer to attenuation = drier and sweeter flavor

This is the gist of it and all I’m willing to absorb, but I’m sure I’ll get into it more later when I understand it a little better. For now, at least I know why there are different strains of yeast.

Thanks to Home Brewing Wiki, here’s a great illustration showing the process: