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Continued Meditation on Brew House Efficiency

by Rob Friesel

After posting Puzzling Out Brew House Efficiency, I shared the link with the local homebrew club, just to see what others might have to say on the subject. (Always tap into the collective wisdom, right?) One member shared a link that helped me think about “where to from here” with this on-going experiment. This post is a think-out-in-the-open style follow up to my previous post, in light of reading this research series posted on BrauKaiser.com.

Article Summary

The BrauKaiser article writes up a series of experiments looking at mash parameters and how they affect overall wort fermentability and brew house efficiency. (N.b., they seem more concerned with the former, vs. my focus on the latter.) Their experiments assess the roles of:

  • Mash time
  • Mash temperature
  • Mash pH
  • Mill gaps (a.k.a., crush size)
  • Mash thickness
  • Base malt types
  • Calcium concentration

For my purposes, I skipped over mill gaps (effectively a constant on my system), base malt types (which in my opinion are recipe design concerns, and their conclusions support my intuitions anyway), as well as mash pH and calcium concentration (mostly due to having insufficient data from prior brew days). From their, I focused on their conclusions, paying particular attention to what they had to say about brew house efficiency.

Mash time

Simply put: longer mash rests at lower temperatures are likely to yield more conversion and a more fermentable wort. This is because mash rests below approx. 152ºF allow the beta amylase to be more stable (i.e., not denature) and therefore carry out their thorough conversions to completeness. Long mash rests at higher temperatures are effectively “pointless” because the beta amylase activity (though more aggressive) arrests as they denature; alpha amylase is more stable at those temperatures but will similarly fully convert during those shorter time periods.

Main takeaway: “low and slow” mash rests are likely ideal for maximizing conversion.

Mash temperature

As mentioned in the previous section, higher mash temperatures will accelerate the enzymatic activity — i.e., increasing conversion rates, meaning shorter mash rests — but this comes at the expense of enzymatic stability and wort fermentability. In other words, a higher mash temperature will likely fully convert faster, but amylase enzymes (especially beta amylase) will denature faster, leaving behind more unfermentable dextrins in the wort.

Main takeaway: “low and slow” mash rests are likely ideal for maximizing conversion.

Mash thickness

The BrauKaiser.com compared thick (i.e., 2.57 L/kg or 1.25 qt./lb.) vs. thin (5 L/kg or 2.4 qt./lb.) mashes over a variety of temperatures, for 60 minutes each. Their research did not find a significant effect on overall fermentability with respect to mash thickness, but they did assert that a thinner mash (i.e., higher liquor-to-grist ratios) correlated with better brew house efficiency. That said, their controlled experiment held mash time as a constant, so the lower mash temperatures with the thiner mashes appear to lower; this is easily accounted for with longer mash rests.

Main takeaway: as a BIAB brewer, thinner mashes are a typical part of the brew day — so I should already be in the ballpark for the “ideal” mash thickness.

Follow-up steps

Having read this article, here are my thoughts on what to do next:

  1. Be more disciplined about pH readings. Target a mash pH between 5.2-5.4 and then get more disciplined about taking those readings. I would like to be able to revisit the mash pH question again in a year.
  2. BHE as a function of mash thickness + mash temperature + mash time? I feel the need to do a series of plots to start comparing these. If I consider the planned O.G. as a predictor of mash thickness, what plots are going to help me make sense of this? Current thinking:
    1. O.G. delta vs. mash thickness
    2. O.G. delta vs. mash time
    3. O.G. delta vs. mash temp
  3. Estimated SRM as a predictor for BHE? Another thought here: I haven’t really looked yet at the color of the planned beers and any relationship to the O.G. delta nor the BHE. Given that malt color can affect mash pH, and that mash pH can affect conversion, perhaps some of these missed marks are because this. If the data suggest that color is having an influence here, perhaps consider re-adopting the “cap with dark grains toward the end of the mash” approach.

About Rob Friesel

Software engineer by day, science fiction writer by night. Author of The PhantomJS Cookbook and a short story in Please Do Not Remove. View all posts by Rob Friesel →

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