Step Mashing

This braukaiser file answers my question! He says:

"The length as well as the temperature of the maltose rest determines the fermentability of the wort. Shorter rests and/or higher temperatures will result in a less fermentable wort as the beta amylase gets less time for maltose production".

Thus, the protein rest is separate and doesn't affect the fermentability; the dextrination rest (alpha) is constant and doesn't affect the fermentability; and only the maltose rest (beta) seems to affect the overall fermentability. Shorter rests and/or higher temperatures result in a less fermentable wort, while longer rests and lower temperatures in the beat range result in a more fermentable wort.

 

"To reduce and eventually terminate the beta amylase activity and to ensure that all starch in the wort has been converted (especially the small starch granules which have a higher gelatinization temperature), a dextrinization rest is held at 158 - 162 *F (70 - 72 *C). At this temperature the beta amylase is quickly deactivated and only the alpha amylase works on the starches. The rest is held until the mash is iodine negative (no starch or long dextrines in the wort). Narziss [Narziss, 2005] and Fix [Fix, 1999] suggest, that a rest at 158 - 162 *F (70 - 72 *C) benefits head retention and body of the beer though glycoproteides that are extracted from the malt but not degraded by enzymatic activity. Because of that Narziss suggests holding this rest up to 60 min."

Thus the alpha stage just converts all the starch and works on the small starch granules that the beta stage has created. The amount that the beta stage has created determines the amount of fermentability.

Thus, based on my understanding, the beta stage does the clipping of the starch chains, and the alpha stage does the conversion of those clipped chains. The more the beta stage clips, the more conversion there will be and thus the more fermentable it will be.

Also, the previous statement in the last message specifically only refers to the beta stage, not the alpha stage.

 

But that's not what Kai says. He specifically states:

"To reduce and eventually terminate the beta amylase activity and to ensure that all starch in the wort has been converted (especially the small starch granules which have a higher gelatinization temperature), a dextrinization rest is held at 158 - 162 *F (70 - 72 *C). At this temperature the beta amylase is quickly deactivated and only the alpha amylase works on the starches."

So if the step is increased rapidly (e.g. by adding a boiled decoction, or adding boiled water), the beta amylase will be denatured at this temperature range (158-162 F). Then ONLY the alpha amylase will be active.

He is talking about adding a boiled decoction, which "quickly" raises the temperature from the beta amylase phase to the alpha amylase phase. The higher the temperature, the more quickly it denatures, so there might be a very short time when it is still active. So, perhaps there might still be a little beta amylase activity while the temperature is rapidly increasing, and while it begins to demature, but it is likely an insignifcant amount.

In the beta amylase range, the alpha amylase is not overly active, but active enough to help the beta amylase out. The beta amylase works on the glucose chains (large dextrines) that the alpha amylase produces. So in that range, the two work together. But in the higher temperature range, the alpha amylase basically works alone, converting the starches to glucose.

I agree. Without more information, it is difficult to determine to what degree the beta amylase is a bigger driver.

 

Regarding the denaturing of the beta amylase, and what I feel is "insignificant", one of Kai's charts shows it denaturing in 30 minutes at a temperature of 150 F, and about 6 minutes at 158 F. So at 162 F, it likely denatures in less than 3 or 4 minutes. So, for the range he is recommending for the alpha amylase (158 - 162 F), the beta amylase would likely denature in about 3-6 minutes, with a rapidly decreasing amount active over that time. Thus, effectively, you might have a couple of minues of beta amylase activity. Over a period of one hour of alpha amylase activity, that is quite insignificant.

[See Figure 4 in the following link}.

https://braukaiser.com/wiki/index.php/Starch_Conversion

 

Sorry, I meant "fermentable sugars": glucose, maltose, etc.

 

Not necessarily. Don't forget that beta amylase denatures at 160 F. That's its maximum temperature. I doubt if it can do it's entire work in a matter of minutes. If so, there would be no need for a beta rest. Why bother with a 15-20 minute rest if it can do its entire work in a couple of minutes at the highest possible temperature? Might just as well only do an amylase rest and cover both bases at once.

 

OK, I'll acknowledge that the temperature of the alpha amylase stage does affect the fermentability - to some extent. But in another article where Kai discusses this same attenuation effect, he makes a qualifying statement. First he says that the graph was only based on using a single temperature rest - not a combined alpha and beta rest ("the rests were held until conversion was complete"). So the graph doesn't show the complete picture where a step mash is concerned, which is what we are discussing. Which means that the experiment you provided is misleading, and not totally relevant.

Secondly, he states:

"The rests were held until conversion was complete. It should also be noted that the exact fermentability will depend on more than the temperature. The fermentability is mainly determined by the time the beta amylase was active. The higher the temperatiure, the quicker the beta amylase is deactivated. This results in less maltose production".

He then provides other factors that affect fermentability, such as the PH level.

See:

https://braukaiser.com/wiki/index.php/The_Theory_of_Mashing

 

The graph is entirely misleading because it only shows the direct relationship between mash temperature and fermentability. Obviously, the higher the temperature, the less active beta amylase is. Thus, without the assistance of beta amylase at higher temperatures, it is obvious that fermentability would decrease. The graph does not show the effect of alpha amylase - by itself - AFTER the beta amylase has had it's effect at lower temperatures. At the higher temperatures it only shows what alpha amylase can do mostly by itself without much help from the beta amylase. Of course the graph shows a sharp decrease. But that does not prove that alpha amylase by itself increases fermentability to any great degree with increased temperature. It actually indicates the exact opposite.

 

I don't think I did at all. Please explain in detail.