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Old 04-24-2010, 05:54 PM   #11
Tiber_Brew
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Quote:
Originally Posted by DavidHawman View Post
Below which they are sluggish and above which they denature, sometimes irreversibly.
Don't mean to pick on you, but denaturing amylase enzymes by excessive heat is always irreversible. Otherwise it wouldn't be denatured.
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Old 04-28-2010, 06:55 PM   #12
Dr Malt
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Dave:

Good question.

The answer to your question about the temperature of amylase breakdown of starch is related to the rate of the reaction as someone here suggested. Chemical and enzymatic reactions increase in rate at higher temperatures. Thus, if you want a reaction to go faster (more hydrolysis of starch in a shorter period of time) you heat the reaction. Enzymes unfortunately are complex proteins of a specific shape to catalyze very specific reactions and have a limit to how much heat they can stand. When these proteins reach too high a temperature, the structure changes in shape so it no longer can catalyze the reaction. This change is irreversible and thus referred to as denaturing. For alpha-amylase that temperature is approaching 160 F. However, this enzyme functions just fine at the physiological temperatures of germinating barley (50 F and above) but at much slower rates. Thus, the 150 F range we use in our mash is just taking advantage of the rate and stability of the enzyme at that temperature to do what we want it to do, breakdown starch.

I hope this help.

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Old 04-28-2010, 08:18 PM   #13
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As Dr. Malt said, the rates of chemical reactions increase at higher
temperatures. Rates roughly double for every 10 C or 18F. Brewers
want the mashing process to go as fast as possible, so they mash
at as high a temp as possible. Above about 170 the proteins unfold
(denature) irreversibly, otherwise you'd mash close to the boiling
point of water to complete the process as fast as possible. The
purpose of the enzyme in the organism is to break down the starch
in the seed to provide fuel for growth, and this process doesn't
happen in 30 minutes or an hour as in a mash, but over several days
at the temperature of the ground.

Related to this is the rate of fermentation. I constantly see remarks
in this newsgroup about how great the yeast was, the fermentation
took off like a rocket etc. but that's not what you want. You want
a slow contained fermentation to minimize byproducts. The rates
of byproduct fermentation increase at higher temperatures just
like the rate of alcohol production. If your fementation blew out of
the carboy, the temperature is probably too high.

Ray

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