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Old 12-05-2010, 05:27 PM   #1
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Default Why does amylase work at high temperatures?

Alpha amylase is optimized to work in germinating barley seeds. They certainly don't get up to the temperatures we use to mash. Why is the optimum temperature, then, for mashing 150-160F? That seems to be WAY outside the logical range for this enzyme.

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Old 12-05-2010, 05:32 PM   #2
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There are many enzymes, and it's oversimplistic to say that alpha amylase only "works" at XXX temperature. Here's some good but simple reading on enzymatic activity and mash temps, along with a chart: http://www.howtobrew.com/section3/chapter14-1.html

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Old 12-05-2010, 07:41 PM   #3
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Alpha amylase is optimized to work in germinating barley seeds. They certainly don't get up to the temperatures we use to mash. Why is the optimum temperature, then, for mashing 150-160F? That seems to be WAY outside the logical range for this enzyme.
Lots of organisms (plant, animal, bacteria) use alpha amylase so it is wrong to say that it is adapted to work in germinating barley.
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Old 12-05-2010, 07:50 PM   #4
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Because evolution does not optimize. Alpha enzyme is most efficient (aka fastest) at 160F, but it works fine, if somewhat slower, at room temperature.

Survival of the "good enough", not the fittest, is the truth. Just look at what a lousy arrangement the human eye is, but it's good enough.

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Old 12-05-2010, 08:51 PM   #5
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Originally Posted by apeltes View Post
Alpha amylase is optimized to work in germinating barley seeds. They certainly don't get up to the temperatures we use to mash. Why is the optimum temperature, then, for mashing 150-160F? That seems to be WAY outside the logical range for this enzyme.
The ~150F mash temperature is the best for brewing beer because that provides the maximum alpha amylase activity for breaking down starch chains into fermentable sugars. As has been said above that is not the only thing alpha amylase might do nor does it mean that alpha amylase does not work at all at different temperature ranges.
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Old 12-05-2010, 09:11 PM   #6
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Originally Posted by david_42 View Post
Because evolution does not optimize. Alpha enzyme is most efficient (aka fastest) at 160F, but it works fine, if somewhat slower, at room temperature.

Survival of the "good enough", not the fittest, is the truth. Just look at what a lousy arrangement the human eye is, but it's good enough.

I'd say it is perfectly optimized to do what it needs to at lower temperatures. The barley produces amylase after it germinates (malting), to turn stored starches into food. It has to be slow for a few reasons.
A growing plant doesn't need a ton of sugar all at once. but rather a slow continuous supply
If you convert the starch into sugar all at once, the water activity inside the seed would drop like a rock and suck the moisture from the growing sprout.
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Old 12-06-2010, 04:04 AM   #7
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Default Yes, but...

The alpha amylase in barley evolved to work best in germinating barley seeds (and evolution, natural selection specifically, DOES optimize things).

Any enzyme tends to have one temperature at which it works best. Any higher or lower, and it loses efficiency. For example, human digestive enzymes work best at approximately 98F. Any higher or lower, and they become less effective.

Why does mashing work best at almost 170F? Why doesn't mashing work best at the temperature at which barley germinates?

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Old 12-06-2010, 04:42 AM   #8
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I'm way out of my league here but will venture a WAG. The efficacy of an enzyme depends upon its shape and its shape is controlled by the charges on the acid residues. Whether an acid residue gives up its proton or not depends on pH and the pK for that residue and the pK depends in turn on temperature. Thus temperature effects the conformation of the enzyme. Coupled with that is the fact that reactions generally take place faster at higher temperatures. OTOH, if the temperature gets too high the enzyme is denatured. Put all these together (if I'm right in my hypothesis) and there is an optimal temperature and pH for each enzyme whether this be the temperature at which it operates in nature or not. Amylases do not need to work at optimum rate to perform their functions in nature nor indeed in brewing. But in brewing speed is important. We don't want to have to wait overnight for the starches in our mashes to convert.

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Old 12-06-2010, 01:24 PM   #9
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Quote:
(and evolution, natural selection specifically, DOES optimize things).
No, check out the efficiency of photosynthesis using chlorophyll. The most primitive photovoltaic cells do a better job.
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Old 12-06-2010, 02:02 PM   #10
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Default Natural Selection and Optimization

Evolution via natural selection doesn't necessarily (or usually) produce the best possible configuration, but that's not what I mean by "optimize". I'm saying that natural selection favors the most adaptive version of a trait given a range of available genetic variation. Thus, for enzymes, we can usually trust them to work best under the conditions in which they evolved.

I think the best hypothesis we have so far is that alpha amylase obviously works well within a very broad temperature range. It's not as "sensitive" as the enzymes I'm more familiar with. For example, many mammalian digestive enzymes slow significantly at a few degrees above normal body temperature (or below). Perhaps we need to mash at such high temperatures to compensate for the reduction in concentration produced when we crush and mix with water? Within limits, reduced concentration equals reduced reaction rate.

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