Multi Rest Mash Order

I've been reading up on mash science recently (geek) and was mulling over the traditional multi stage mash schedules, particularly popular in Germany.

Why do they tend to start with a low temperature rest and then increase?

As far as I can tell the logic suggests starting at a higher rest (say 72 C) would get the Alphas well under way, breaking down starches into longer chained sugar molecules.

Then the Betas could work on those sugars turning them into fermentables, which you could assist by dropping the temperature down to, say, 63C.

If so this would be uber efficient.

I know this must be wrong since hundreds of years of experience have not changed the prices - along with the extensive research from the past 70 years.

But why?

Have the betas already been so damaged from the upper rest?

(this does, of course, ignore the low lower rests).

Among you bunch of homebrew geniuses I'm guessing you can enlighten me...

Cheers.

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The higher temperatures will denature the enzymes that work at the lower temperatures. So you cannot go from high to low for the full mash.

Decoction mashing accomplishes exactly what you propose. A portion of the mash (containing a lot of starch but relatively little enzyme) is converted fully at a high temperature and then boiled and then added back to the rest of the mash which contains a lot of enzymes and less starch so those enzymes can work on the converted starch at lower temperatures.

remilard said:

The higher temperatures will denature the enzymes that work at the lower temperatures. So you cannot go from high to low for the full mash.[...]

Click to expand...

Exactly. Once denatured the beta amylase ain't coming back to life. It's done.

If I remember my reading there are around 8 different enzymes in malt that, depending on the degree of grain modification, protein content, mash pH and the brewer's goals (and probably something I missed listing), could benefit from specific rests...

Cheers!

Don't forget, the temps listed are for optimal activity. They still work just fine at lower temperatures. They are all active together as long as it is below the denaturing temperature. If you are doing a protein rest, both of the amylases are still doing their job, just at a slower rate (still pretty fast though). These are the same enzymes the seed uses to germinate in the cool ground in the Spring. I'm not sure what the relative levels of alpha versus beta amylase are, or their relative reaction rates. It could very well be, that even at say 148 F that there is enough alpha amylase activity to provide beta amylase with substrate such that it's activity is saturated (i.e. no way to speed it up).