I am new to home brewing but have made several very tasty batchs. I am designing an all grain recipe on my own. I am confused on Apparent Attenuation. if my yeast lists the attenuation as 67% and my target OG is 1.053 then my FG should be 1.017? I took 53 multiplied it by .67 telling me that my gravity will drop from 53 down about 36 points to 1.017? the reason i am confused is that when i put this recipe into any online calculator it shows 1.014 as finishing gravity. what am I doing wrong? or am I just completely misunderstanding attenuation?
Your math is correct. But... The calculator(s) must be assuming a different apparent attenuation than 67%. By the way, the fact that a yeast manufacturer gives a typical attenuation value is almost meaningless. Besides yeast strain, other factors affecting attenuation include the grain bill, mash temperature, and mash length. All three of these grain/mash related parameters affect the attenuability of the wort. Unfortunately, most programs/calculators ignore at least one of these parameters.
ok, thank you. In one way I am happy I was not mistaken in my understanding of attenuation. However now I dont know how to get an estimate of the ABV before I brew the beer and get a OG and FG. Much more study is needed on my part I am guessing?
In my experience, wyeast and whitelabs yeasts usually complete near the top of the estimated attenuation range. What yeast is it? Because 3711, for example, often attenuates 85% of sugars or more, which is quite a bit higher than the estimate. if it goes to 64%, the FG would be 1.19 to 67% would be 1.0175 to 70% would be 1.016 the above shows a gravity range of .003, which is equal to about 0.4% ABV differential
It's not so much an academic exercise, but a practical one. The more you brew the greater your understanding of efficiency (OG) and attenuation (FG) in your system. Somewhere in the software there is a "tweak" to manually adjust the yeast's attenuation (usually called "custom attenuation"). For starters, pick some where in the mid point of the mfg's specs or just accept the software's default numbers. This is heavily influenced by mash temp and yeast health and somewhat by grain bill. Brew a lot, keep notes, and you'll start to get a good feel for the parameters of each strain. Related: your OG is a mystery until you nail down your efficiency. Your previous commercial recipes had an assumed efficiency (probably around high 60s or low 70s) but that can bounce around depending on quality of crush and your sparge technique. Accept the fact you'll be off a few points until you figure it all out (aka; the joy of brewing).
You don't have to guess about attenuation. It's always an estimate, but some are more likely to be good estimates than others. BeerSmith is very popular and it considers all the factors I mentioned except for grain bill. BrewCipher considers them all and also has a "power knob" to dial the model in to your own brew house results. (In fact, the issue you are pondering right now was a major reason for developing BrewCipher.)
