I've done some looking around, but can't seem to find a decent answer to this question, so I'll pose it here. I'm trying to replicate a commercial beer. The beer starts at 13.5 Plato and is 5.2% alcohol, according to the brewery's website. In gravity terms, this translates to approximately 1.055 OG and 1.016 FG. My latest attempt, using Wyeast 1728 (Scottish Ale), mashing at 153, and fermenting at 67F gave me a FG of ~1.013 and I nailed the OG. So my question is, given a particular yeast strain, a particular mash temp, and OG and FG numbers, is it possible to calculate how much a change in mash temperature will affect the attenuation, and corresponding FG, if other factors (grain bill, fermentation temp, water chemistry, etc.) are assumed constant? Obviously, I know that a lower mash temperature will yield a more fermentable wort, and vice versa, but by how much? Also, I have a related question regarding yeast - the attenuation numbers listed on the Wyeast specs - what do they even mean? Are they based on a particular mash temperature and grain bill, or what? Because it seems to me there are far too many variables that affect attenuation for them to serve any purpose other than comparing yeast strains to one another, but it might be helpful (or at least, satisfy curiosity) to know how they are actually calculated.
I'm pretty sure that unless you're in a controlled laboratory experiment where you can control yeast pitching, viability, mash temps, mixing, etc etc etc you're not going to have an accurate answer to your question. A vague number that varies a bit? Maybe. I think your best bet if you want to clone that beer is to make a few good assumptions, brew it a bunch, adjust after each brew, take meticulous notes and hone in on the taste you want. For instance, try keeping everything else constant and mash at 155F next time to try to raise your FG.
Do you think there is a problem with your beer because it finished 3 points lower? I believe that there are too many factors to come up with any formula to accurately predict final gravity from mash temp,O.G., and yeast strain.
This question is asked all the time. Yes, you can calculate this number within +/-1 point of FG based on these variables. Cue @VikeMan.
No, I'm sure the beer will be great. But I do think that to nail the mouthfeel of the beer I'm trying to make, it's important to come as close as possible to the ABV and residual sugar content in that beer. And while I agree that the sheer number of variables involved makes it impossible to accurately predict for any one recipe, having some actual data and several constants to plug into a formula for this particular beer ought to make it easier to predict, at least within an acceptable margin of error, what my mash temp ought to be next time around to finish 3 points higher. And I also have data from a prior attempt using a different yeast that could likewise be used, should it turn out I like that yeast better.
BrewCipher models attenuation based on yeast strain, grain bill, mash temperature, and mash length. You are wise to question this. By and large, I don't even find them useful for comparing strains to each other.
So, plugging in my batch specs to BrewCipher gave me a higher attenuation and lower expected FG than I actually got - by over 2 gravity points. I'm curious as to how you've modeled this.
Basically, It's modeled based on yeast strain data and grain data from Greg Doss, mash temp data from Kai Troester, and mash time data from both Greg Doss and Kai Troester. And some extrapolations thereof. There are lots of reasons why your results could be different than predicted. here's some... - Factors not modeled in attenuation part of the model (e.g. pH, yeast pitch rate, yeast health, oxygenation rate, nutrients, methods used to combine grist with brewing liquor, mashout/no mashout, mashout time). Many of these would be minor, but there's no data to model them from, and little things can add up. - Measurement error (either in the data the model was built from or in your batch) The above non-modeled factors (and even measurement errors) tend to be brewhouse specific. If you look at the Brewhouse parameters tab, there's an Attenuation Power factor you can use to minimize (or eliminate) the average difference between the modeled attenuation and actual atenuation. When you hover over that cell, there's a popup comment explaining how to use it.
2 points is really not that bad. I consider 1 point to be pretty good. Are you measuring using a hydrometer? Measurement accuracy with that tool is +/- 1 point on its own.
