Role of Alpha and Beta Amylase

[jan23778]

Hi,

I consider myself as a relatively advanced homebrewer but I have always had a question that I have never been able to completely answer. I was wondering if anyone had any views.

I understand that in brewing the Alpha (and Beta) Amylase breaks down complex carbohydrates into simpler sugars in order for the yeast to be able to ferment and produce CO2, alcohol and other compounds.

The Alpha and Beta Amylase are produced in the seed through Germination/Malting.

My question revolves more around the use of the enzyme for the plant, though.

The plant supposedly generates the enzymes for the same reason; to break down the complex starches it holds within its kernel in order to provide sugar and nutrients for the plant whilst it is still in the ground and unable to do this for itself (due to lack of sunlight) a sort of plant breast-milk, if you like. But, Beta Amylase (which has the lower temperature range of the two) is only active from 54°C or 130°F.

Given that the vast majority of all plants on this planet germinate at a lower temperature than 54°C, surely neither of these Amylase enzymes would be active. Meaning the starches wouldn’t convert to sugars. I can appreciate that at a slightly lower temperature they may activate but more slowly, but wheat and barley crops are grown in much lower temperature areas, so I don’t buy that.

Does this mean that the plant uses starch reserves (instead of more simple sugars) to create the nutrients it needs and the enzymens are not used? And if so, why haven’t these unused enzymes been eradicated by evolution over the tens of thousands of years of the grain’s history.

 

[Homercidal]

Good question. Remember that alpha and beta amylase are only two of the many enzymes a barley kernel has in it. I'm guessing that some of the others function at other temperatures. And while they may be fine for growing a plant from a seed, it's the alpha and beta that are more useful in brewing. Happily their activation temperatures overlap so we can take advantage of both with 1 temperature rest. But some brewers also use other temperatures for various things like a Cereal Mash, Protein Rest, etc.

A quick peek on Google shows that Barley germinates at a lowest temperature range of about 34-36F. There must be some enzyme that activates at that temperature when wet.

 

[govner1]

As I recall from my Biology classes (a LONG time ago) rehydration causes the seed(s) to germinate. As a part of this rehydration the cells in the outer layer(husk) of the endosperm produce & release enzymes such as amylases that breakdown the starches stored in the endosperm. This creates the simpler sugars.

 

[jan23778]

Hi Homercidal,

Thanks for the response. Yeah, it must be something along the lines of what you suggest as I can't think of anything eslse it could be. Strange though, as even on some horticulture websites I have seen it suggests that it is the Amalyses that do the same work in plants that we are so familiar with in brewing.

The lowest temperature enzyme rest I am familiar with regarding brewing is Phytase or Acid rest which is in the region of 30C or 86F. Maybe there are some that we brewers aren't familiar with that activate at lower temperatures but are not documented because they are no use to brewers.

Perhaps I should be posting this on a horticulture - thinking about it this is exactly what I will do.

Thanks again

 

[jan23778]

Hi govner1,

Thanks for the response, you are absolutely correct, my issue is with the temperature it does this at. Beta amylase is active at 130Fish but I cannot believe that a plant will produce enought heat on its own to reach this temperature.

I get a mental image of a cartoon grain with steam pillowing out of its head.

 

[ajdelange]

I can appreciate that at a slightly lower temperature they may activate but more slowly, but wheat and barley crops are grown in much lower temperature areas, so I don’t buy that.

This is a good question and one I am certainly not qualified to answer but common sense would seem to indicate that what you don't buy is probably the explanation. The germination process is much slower than the conversion in the mash tun and so much lower reaction rates are acceptable. Though reaction rates depend on a lot of things I believe there is a rule of thumb that a 10 K temperature change typically doubles a reaction rate. Based on that, which may not really be applicable here, we would expect a reaction at 0 °C to proceed at a rate 1/(2*2*2*2) = 0.0625 times its rate 40 °C. What takes an hour in the mash tun would take 16 hours in the plant at 0 °C

 

[Tiber_Brew]

They way it was explained to me was this:

The "active" temperature ranges you read about for enzymatic conversion in brewing are actually just optimal temperatures for a mash in the brewing purposes. The enzymes are active at much much lower temperatures as well, just at a much slower rate. At typical room temperature, conversion takes days - not minutes, but that's about the rate at which the seed consumes the saccharrides before the cotyledons become the source of energy. There is a lower and upper temperature limit for enzymes to be active, but it's wider than the "optimal" ranges given for brewers.

A mash is just a somewhat controlled means of speeding up the saccharification process.

 

[jan23778]

Ok, yeah. That would make sense. I had discarded that as I just couldn't get my head around enzymes being active at such a massive difference in temperature, I thought they needed more specific parameters. But given the massive difference in speed of conversion; minutes v days, that does make sense.

Many thanks to all for your help

 

[ajdelange]

The "active" temperature ranges you read about for enzymatic conversion in brewing are actually just optimal temperatures for a mash in the brewing purposes. The enzymes are active at much much lower temperatures as well, just at a much slower rate. At typical room temperature, conversion takes days - not minutes, but that's about the rate at which the seed consumes the saccharrides before the cotyledons become the source of energy. There is a lower and upper temperature limit for enzymes to be active, but it's wider than the "optimal" ranges given for brewers.

According to the Arrhenius law there is no upper or lower limit. When the reaction is catalyzed by an enzyme, however, we have to recognize that an enzyme is a protein and that proteins denature if they are heated above a certain temperature. Thus the 'optimum' for an enzyme in brewing occurs at the temperature at which increase in rate from the Arrhenius law is more than offset by the loss in rate caused by denaturing. This is why the rate curves you see run up gradually, roll over and then plummet.

This model says that there is an upper limit but now lower limit. But note that the decrease as temperature is reduced is exponential with temperature implying such slow conversion at really low temperature that the rate is practically speaking 0.

 

[Tiber_Brew]

According to the Arrhenius law there is no upper or lower limit. When the reaction is catalyzed by an enzyme, however, we have to recognize that an enzyme is a protein and that proteins denature if they are heated above a certain temperature. Thus the 'optimum' for an enzyme in brewing occurs at the temperature at which increase in rate from the Arrhenius law is more than offset by the loss in rate caused by denaturing. This is why the rate curves you see run up gradually, roll over and then plummet.

This model says that there is an upper limit but now lower limit. But note that the decrease as temperature is reduced is exponential with temperature implying such slow conversion at really low temperature that the rate is practically speaking 0.

Right. Try growing seeds in a freezer. Or in boiling water. Practically speaking, there are general limits, and then there are the recommended brewing ranges.

I've not heard of the Arrhenius Law, but I'll give that a read.

 

[ajdelange]

Actually it is the Arrhenius Equation. Start at https://en.wikipedia.org/wiki/Arrhenius_equation.

 

[Tiber_Brew]

Actually it is the Arrhenius Equation. Start at https://en.wikipedia.org/wiki/Arrhenius_equation.

Thanks

 

[helibrewer]

Yes, the plant has days to accomplish this, we are forcing things to happen in 15 min to an hour.

 

[jan23778]

Hi,

It looks like a-amylase has a secondary trigger (other than temperature).

https://en.wikipedia.org/wiki/Gibberellin

Bibberellins are acids that actually initiate a-amylase action:

"Usually in germination, the breakdown of starch to glucose in the endosperm begins shortly after the seed is exposed to water.[8] Gibberellins in the seed embryo are believed to signal starch hydrolysis through inducing the synthesis of the enzyme α-amylase in the aleurone cells."

 

[ajdelange]

The rate at which amylase operates depends on temperature but if there is no amylase then it doesn't really matter what the rates are. Apparently there is no amylase until the aleurone cells are triggered by certain gibberellins to produce some. And giberellins production is apparently triggered by water.

So dry grains in a freezer or in a bin in Coober Pedy: No water, no gibberellins, no amylase
Mash in a freezer: lots of amylase but very low rate constant = conversion takes forever
Mash at room temperature: Same but higher rate constant = conversion takes days
Mash at mash temperature: Same with higher rate constant still = conversion takes minutes
Mash at high temperature: amylose denatured = conversion stopped.

Barley corn in the ground in spring: water triggers gibberellin production. Gibberellins turn on genes which cause production of amylase. Weather is cool but warm enough that amylase rate constant allows enough starch to convert to glucose to feed the embryo.

Please note that all this is way above my pay grade. All my experience of giberellins is related to experiments I did in college on certain botanicals which botanicals were not, so to speak, approved of.

 

[Tiber_Brew]

Please note that all this is way above my pay grade. All my experience of giberellins is related to experiments I did in college on certain botanicals which botanicals were not, so to speak, approved of.

It's amazing what one can learn through such experimentation, isn't it?