Mash temperatures

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DavidHawman

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This question has been bugging me ever since I started reading about mashing. The amylases in the seed become most active at ~150F and denature around ~160F hence brewers aim to mash at temperatures around that. Enzymes, for the most part, function in a narrow band of temperatures. Below which they are sluggish and above which they denature, sometimes irreversibly.

My question is: Why is that temperature for the amylases so high? Most enzymes in the human body are most active at 98.6F since that is the environmental temperature they operate in the most.

So it stands to reason that the seed enzymes would be most active around 60-70F or the temperature of the ground when they germinate but instead they are double that. I doubt you would find a single enzyme in the human body that would be more than barely functional at 180F let alone in its most active state.

Conversely, if an enzyme is most active around 150F then what use is that for the seed if it never reaches anywhere near that temperature while germinating since the enzyme will be incredibly sluggish?

What am I missing? :confused:
 
Interesting question.

This might shed some light:

Since a wide variety of organisms, including humans, can digest starch, alpha-amylase is obviously widely synthesized in nature, as opposed to cellulase. For example, human saliva and pancreatic secretion contain a large amount of alpha-amylase for starch digestion. The specificity of the bond attacked by alpha-amylases depends on the sources of the enzymes. Currently, two major classes of alpha-amylases are commercially produced through microbial fermentation. Based on the points of attack in the glucose polymer chain, they can be classified into two categories, liquefying and saccharifying.

Because the bacterial alpha-amylase to be used in this experiment randomly attacks only the alpha-1,4 bonds, it belongs to the liquefying category. The hydrolysis reaction catalyzed by this class of enzymes is usually carried out only to the extent that, for example, the starch is rendered soluble enough to allow easy removal from starch-sized fabrics in the textile industry. The paper industry also uses liquefying amylases on the starch used in paper coating where breakage into the smallest glucose subunits is actually undesirable. (One cannot bind cellulose fibers together with sugar!)

On the other hand, the fungal alpha-amylase belongs to the saccharifying category and attacks the second linkage from the nonreducing terminals (i.e. C4 end) of the straight segment, resulting in the splitting off of two glucose units at a time. Of course, the product is a disaccharide called maltose. The bond breakage is thus more extensive in saccharifying enzymes than in liquefying enzymes. The starch chains are literally chopped into small bits and pieces. Finally, the amyloglucosidase (also called glucoamylase) component of an amylase preparation selectively attacks the last bond on the nonreducing terminals. The type to be used in this experiment can act on both the alpha-1,4 and the alpha-1,6 glucosidic linkages at a relative rate of 1:20, resulting in the splitting off of simple glucose units into the solution. Fungal amylase and amyloglucosidase may be used together to convert starch to simple sugars. The practical applications of this type of enzyme mixture include the production of corn syrup and the conversion of cereal mashes to sugars in brewing.

Thus, it is important to specify the source of enzymes when the actions and kinetics of the enzymes are compared. [...]
Click to expand...

http://www.eng.umd.edu/~nsw/ench485/lab5.htm

Anyway, what I took from that is that the source of the alpha-amylase determines in part how it behaves. So maybe the alpha-amylase used by the human digestive system works best at ~98.6F, but the alpha-amylase in grain works best at ~150F.
 
Sounds like you are angling for proof that the Gods love us and have stuck this enzyme in barley so we could make beer. ;)

It is a good question, are these enzymes active at lower temps at higher pH's? Are they active in the plant (as opposed to the seed) at lower temps? Possibly, when the plant is growing, there are other chemicals that make the enzymes active at lower temps. I think you would need a degree in botany to answer this one.
 
It's more complicated than that. Beta amylase is most active between 130-150F, alpha doesn't de-nature rapidly until 165F. The main starch enzyme in your body is alpha amylase. Nature has a lot of "good enough" processes. If it all made sense, we would be producing Beano in our guts. It can breakdown almost any complex sugar at body temps.
 
I guess my question is that biologically speaking, enzymes in organisms are tightly bound to the environmental conditions the organism grows in. Why are the amylase enzymes of barley so outside the temperature ranges of a seed?

Evolution has tailored the enzymes of living organisms to operate at peak efficiency at the conditions of the enzyme's environment. Human stomach enzymes work at a pH of 2 or 3, those in the blood at a pH of about 7. Enzymes that operate outside normal parameters are sometimes reporting enzymes that act to trigger mechanisms to bring the organism back to normal but I don't see amylase doing this.

The amylase enzymes of barley seems to violate this close tailoring. I doubt very much that if you plant a barley seed in soil at 150F it would grow because nearly all its enzymes would denature. Yet, the seed contains amylase enzymes that are highly active at this temperature.

pkeeler's suggestion of pH and cofactors could explain this but it seems quite a stretch that a simple pH change could allow an enzyme to function at twice its normal temps...

Ah the wonders of science.
 
There are ideal temperatures for enzymes to work, however at the same time life is about trade-offs. Even though a-amylase may work best at higher temperatures, 150 to 160 degrees would be too high for many other biological processes. So body temperature may be contained within a certain boundary in order to maximize total body function rather than benefiting solely the function of a-amylase.
 
From an evolutionary standpoint, perhaps the rate at which the enzymes function under typical plant conditions, is sufficient and more beneficial than at a greater rate.

For example, in our own bodies, we benefit from complex starches because they provide a more sustainable source of energy, and in the same way, perhaps the slower rate of conversion of polysaccharides to mono/di-saccharides provides an energy source, while holding starches whole for later use. After all while we store energy as fat, plants store it as starch.
 
DavidHawman said:
So it stands to reason that the seed enzymes would be most active around 60-70F or the temperature of the ground when they germinate but instead they are double that. I doubt you would find a single enzyme in the human body that would be more than barely functional at 180F let alone in its most active state.

Conversely, if an enzyme is most active around 150F then what use is that for the seed if it never reaches anywhere near that temperature while germinating since the enzyme will be incredibly sluggish?
Click to expand...

We need the starch to convert in an hour, the seed doesn't. What does it matter if it's sluggish if it's got days to get it done?

I don't have any data to back that up, just makes sense to me.
 
Does unmalted barley contain amylase enzymes? If so, why do we use malted barley, rather than unmalted?
If the enzymes are produced as a by-product of the malting process, isn't it reasonable to assume that those enzymes are going to be active at something similar to the kilning temperatures experienced during the malting?

-a.
 
Kilning is not exactly a natural part of the barley life-cycle, considering it's the arrest of development which stops further growth of the sprouting grain, before it can utilize more starch for growth. The enzymes are produced via germination, which is mostly at room temperature.
 
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.

Dr Malt :mug:
 
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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