Conversion progress in a single infusion mash

This was my contribution to the most recent Basic Brewing Radio / BYO listener experiment. It was also the first time that I was able to contribute.

When brewing my most recent KaIPA, I took iodine tests and mash gravity readings during the mashing process. The grist consisted of

  • 90% Bairds Pale Malt
  • 4% Weyermann CaraMunich I
  • 6% Weyermann Munich II

Mash temperature was 68 C at a mash thickness of 3.5 l/kg and a mash pH of 5.45. The mash was stirred before a sample was taken.

This is the progression of the iodine test:

At the 30 min mark I considered the iodine test negative.

The progression of conversion efficiency looked like this:

After 30 min, when the iodine test was negative, only 90% of the extract potential of the grain had been released into the mash’s sweet wort. If I would have run-off at that point efficiency into the kettle would have suffered about 8-9% (conversion efficiency needs to multiplied with the lauter efficiency if efficiency into the kettle is needed). Mashing another 30 min gave me the additional 10% extract potential from the grain.

To what extent the attenuation was still changing after 30 min I don’t know. But I assume that there wasn’t much change happening due to the relatively high mash temp which denatures the beta-amylase more quickly.

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