Explain It To Nick: Mash Thickness

Exactly. Just because you've converted starches to sugars doesn't mean your yeast can ferment all of those sugars. Fermentability is mostly based on two factors: mash length, and yeast strain. Some yeasts like 3711/Belle can ferment every damn thing under the sun down to 1.002 every time. Other yeasts like Windsor can't ferment even the simplest sugars worth a frick. However mash time is also a tool in your toolbox that can be used to either reduce or improve fermentability. The longer the mash, the more simple fermentable sugars will be produced, and conversely, a very short mash of say 15-20 minutes will ensure much less fermentable sugars in the rare case where you want a lot of body and don't care about high ABV. But just because your starches are converted, doesn't mean your yeast can ferment very much of it. Whether people know this fact or not, this is really why most people mash for a full hour or more, is to ensure a high degree of fermentability / attenuation, NOT for purposes of efficiency which largely occurs within about the first ~20 minutes of the mash. Based on tons of experimentation & experience, I mash most batches for 45 minutes these days (used to be 40) for purposes of FERMENTABILITY, NOT efficiency. I can get excellent efficiency every time in just 30 minutes. It's the "normal" FERMENTABILITY of about 70-80% that I'm really aiming for with my mash time of ~45 minutes. I could mash longer, but... diminishing returns beyond that point, honest to golly.

 

Mash temp and the makeup of the grist can also be significant knobs. For some reason known only to Ninkasi most brewing software ignores the grist component, which is why we get so many posts like "My Imperial Stout fermentation is stuck at 1.030. Should I add some champagne yeast?" (A two-fer.)

 

Right again. Cheers.

 

That is an exaggeration. Windsor can ferment the simpler sugars of Sucrose, Glucose, Maltose, Fructose,…

It is Maltotriose that Danstar Winsor has ‘issues’ with as detailed on the Lallemand website:

“Windsor does not utilize the sugar maltotriose (a molecule composed of 3 glucose units). Maltotriose is present in wort in an average 10-15% of all malt worts. The result will be fuller body and residual sweetness in beer. Be advised to adjust mash temperatures according to desired result.”

http://www.lallemandbrewing.com/product-details/windsor-british-style-beer-yeast/

Cheers!

 

Yes, that was an exaggeration. I'm a grumpy old man.