Will mixing boiling water with malt flour deactivate the malt enzymes?

I’m trying to adapt a recipe for mämmi that involves mixing mixing a combination of malt+regular flour with boiling water in a 1:2 ratio (by weight) and need to understand whether the point is to stop the enzymes or to encourage their action.

Overall it is add 3 parts boiling water to 1 part malt, then 2 parts regular flour, off the heat. Mix and let sit.

  • Hard to say - how hot is the remaining mixture. Looks like amylase is most active between 55 and 65 C. – bob1 Mar 28 at 21:26
  • @bob1 2 parts water to one part flour , so it might be mixture temperature might be as high as 80C. More worried about the initial shock – Dave Mar 28 at 21:35

Yes, heating to boiling temperature will destroy amylase.

Depending on the ratio, the goal of that recipe may be to destroy the enzymes, to gel the starch, or to help the enzymes be most effective. It’s not uncommon for particularly old and traditional recipes to use a combination of boiling water, ice-cold water, and room-temperature ingredients to reach a particular temperature, as the ratio of inputs will determine the final temperature pretty accurately without a need for a thermometer. If the water to malt/grain ratio is about 1:1 by mass, that would put the enzymes at their optimum temperature for converting starch to sugar. If it’s a lot more water than malt/grain (again, by mass) then the purpose is more likely to deactivate the enzymes and/or gel the starch.

  • According to this article on Wikipedia: en.wikipedia.org/wiki/M%C3%A4mmi - the enzyme activity is importnat, so presumably is it important not to get the mixture too hot. However, maybe the maltase isn't harmed by high temperature while it is dry, so perhaps the water has time to cool while the malt-flour is soaking? (as an aside, note the links at the bottom of that article, they may be useful) – j4nd3r53n Mar 29 at 7:35
  • @j4nd3r53n Dry heat denatures enzymes just as surely as wet heat does (and it doesn't need to be boiling temperature. Most proteins are reliably destroyed once they reach 65 °C, only very few, most from specialised organisms, survive higher temperatures). – Konrad Rudolph Mar 29 at 8:16

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