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Mash and lauter efficiency

I brewed three batches on Sunday. Two infusion, one decoction.

For the first six batches I’ve done, all infusion mash, my volumes have all been off post-boil. My pre-boil volumes are close, but never quite there. For example, I expected 7 gallons pre-boil from my Patersbier and ended up with 6, which translated into 4 after a 90 minute boil. (I am wrongly assuming 18% per hour boil-off)

My seventh batch was a Hockhurz double decoction Oktoberfest, and every number (temperatures, gravities, pre/post boil volumes) was on target. Aside from the time impact, I found the decoction mash easier to manage than my infusion mashes.

What I can’t wrap my head around is why I’m coming up light in my infusion mashes. I’m stopping my sparge when the gravity reads about 1.008, per Palmer. (I tried checking pH but the time and temperature correction and keeping the device calibrated was more work than I wanted to do on brew day). While I am using the wrong volume assumption for boil-off, I’m struggling to think what I could change:

  • I use 1.5 as my mash thickness for the infusions. I used 1.8 for the decoction.
  • I use 3 quarts as my tun deadspace
  • I assume 20% gallons-by-weight grain absorption
  • My mash temperatures vary by up to + 2 degrees; I usually target 152 for my sacc’ rest.

I could see dropping my mash thickness and increasing my deadspace compensation, and subsequently sparging with more water. But since I’m stopping when the gravity reads 1.008 (or thereabouts), this seems foolish – the same net volume of water is flowing around, I’m just sparging with more.

I adjust mash and sparge pH via Bru’n Water. Using yesterday’s mashes (Dunkelweizen, Patersbier, Oktoberfest), the sparge pH was constant (5.6 adjusted with 88% lactic acid), mash pH was constant (5.4 adjusted with calcium hydroxide [Oktober, added to grain at dough-in] and/or 88% lactic acid [Dunkel and Patersbier]), just the thickness and mash scheme changed.

When doing iodine tests, my Dunkelweizen and Oktoberfest converted nearly completely, but even after extending the 152 sacc’ rest my Patersbier was still showing light purple on my test stick. I could see that the Hockhurz mash, with extended stops at beta and alpha amylaze activity, would convert more and therefore leave more sugar in solution, but my Dunkel at 152 sacc for 60 minutes converted roughly the same amount (given the color indications on my starch test).

Ideas appreciated!


Two thoughts - first, boil-off is best calculated as a rate (one gallon per hour, for instance), not a percentage, since it’s a constant under a given brewday’s conditions (kettle dimensions, ambeint temp and humidity, BTUs delivered by burner, etc.), and second, grain absorbs one lb of wort for each lb of grain or 0.125 gallons/lb.

A third thought - you don’t state your assumed efficiency, but if you hit better numbers on the decoction it’s possible that you are shooting too high and thus using less grain that you should for the infusions.

On the first point, I’ll play with your approach a bit but that doesn’t seem right – given all of those constants, wouldn’t it be some sort of compounding decline? Thinking about that, though, I guess that if the BTU rate is constant… then boil-off should be constant.

So 12.5% versus my 20%. If I’m assuming 20% in my math, and I stop my lauter at ~1.008, you are implying that I’m diluting the sugars towards the end of the lauter and therefore stopping it sooner than I should?

This. I went in assuming 80%. I’ll adjust it down 10% and collect all of the variables for Kai’s efficiency calculator during my next brew session.

To probe your intuition here, is it because a decoction (given the times and temps) typically has a higher efficiency due to longer conversion times (especially the hockhurz, with the 144 and 158 steps)?

Thanks for your insight.


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