Like, for example, if you select a yeast with an average attenuation of 80%, but you mash at 160, which limits attenuation to 76.8%1, would the limit simply be the lower of the limit or the average attenuation? (76.8) or would you multiply the limits? (like 0.77*0.80 ~=61%)

Further, does anyone know if a more detailed breakdown than the one linked (pasted for convenience)

140ºF (60ºC)    149ºF (65ºC)    160ºF (70ºC)    167ºF (75ºC)
87.5%           86.5 %          76.8%           54.0 % 

[1] http://www.homebrewtalk.com/wiki/index.php/The_Theory_of_Mashing

  • 2
    The attenuation ranges specified for yeast do not apply to your wort. They are merely provided by yeast labs for you to be able to compare yeast strains from the same lab. Those numbers come from fermenting a standardized (for their lab) lab specification wort that may have little bearing on your particular beer. Also many other other factors affect attenuation besides wort, including pitching rate, yeast's health and prior history, yeast strain, availability of yeast nutrients, alcohol level, temperature, and other competing microorganisms. Sep 30 '14 at 20:47
  • Let's assume, for sake of the question, that the "average attenuation" is not taken from what the mfg states, rather it is an average of what you get for that yeast with that beer style (all other things being equal). You are only wanting to know how additional changes in mash temp will affect attenuation.
    – Wyrmwood
    Sep 30 '14 at 22:26
  • Sorry, on the second question, I am not aware of a resource like that. I think it would be hard to put together because you will have variability even if you could keep mash temp stable to laboratory degrees of precision because wort fermentability likely correlates with water-to-grist ratio, mash pH, and sparging technique. On the first question, it seems like you would still have variability -- each yeast cell has its own preferences and limit for fermenting the sugars from the most readily fermentable (glucosse) to more difficult to ferment (like maltotriose). Oct 1 '14 at 16:13
  • 1
    This is not a direct answer, but doing a forced ferment test on your wort is highly recommended to determine the attenuation limit for that particular wort. Oct 1 '14 at 16:14

I think you are over thinking and and mis-interpreting the point of the "theory of mashing" article. That table regarding mash temp and attenuation is only specific to the wort tested. It's meant as a demonstration of how increasing temps may make a less fermentable wort.

Fermentability of a wort is based on much more than temperature of the mash. The composition of the grist can have a much bigger effect than temp alone. Manipulating temps is a tool for overcoming the limitations of the grist. Consider the differences between three grists: 100% 2-row, 50% corn- 50% 2-row, 50%corn 50% Munich. In each case the total diastatic power of the grist is different. If you mashed each one at the same temp you'd likely get three different attenuations. There is no way to calculate the fermentability of your wort. It can only be tested.

In general, you are correct however in assuming that which ever factor is the least attenuative that will drive your attenuation. A 100% fermentable sugar solution will only attenuate to the level that the yeast can tolerate the alcohol or lack of nutrients. Where as if you make a wort that contains 30% non fermentables; a yeast that can go to 80% attenuation will stop at 70% attenuation because there is nothing left to ferment.

  • 2
    Yeah, the concept of non-fermentables in the mash (crystal malt, partially kilned malt, etc) totally ruins any chance of having the formulas in the question be practical at all.
    – Graham
    Oct 1 '14 at 14:52
  • And if the mash temp limited the wort to 75% fermentable, but your yeast could only handle 70, you'd get ~70?
    – Wyrmwood
    Oct 1 '14 at 15:53
  • Right @Wyrmwood. There are many variables in brewing and calculating any # to much exactness is not really a strong science.
    – brewchez
    Oct 1 '14 at 15:55
  • Right on @Graham!
    – brewchez
    Oct 1 '14 at 15:56
  • On this topic, I am reading Brewing with Wheat, and I am struck by how the brewers change their mash profile for each batch of grain, knowing that while it all may be wheat, the wheat from one particular farmer is different than the wheat from another. Oct 1 '14 at 16:16

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