Step mashes, enzymes and amyloglucosidaise (oh, my!)

[Brooothru]

So most all grain brewers are at least conversant in the temperature bands for maximizing and manipulating the mash to highlight beta amylase and/or alpha amylase to produce either drier and higher alcohol beers or maltier and more dextrinous ones. Some of us have played around with amyloglucosidaise in either (or both) the mash tun and the fermenter to break down some of the more stubborn starches and dextrins to provide very dry and crisp beers.

Beta amylase is optimized between 131F-150F to produce maltose. Alpha amylase is optimized between 154F-162F and produces a variety of fermentable sugars in addition to maltose. Both enzymes are less active outside those temperature bands but still convert starches to fermentable sugars outside those optimal ranges. Both enzymes are denatured at mashout temperatures. Single temperature mashes choose a 'Goldilocks' in-between temp to favor one enzyme over the other while still utilizing both. Step mashes strive to capture both enzymes in sequence at the most optimum temperature for each.

Then comes 'gluco'. This enzyme attacks the limit dextrins alpha 1,4 and alpha 1,6 thus hydrolyzing and converting starches that wouldn't be converted by either beta or alpha amylase enzymes. Gluco becomes denatured at temperatures above 140F, which is lower than most beta rests in step mashes and is completely below the temperature for any single temp mash.

Since I'm not a biochemist and haven't studied this topic since freshman Organic Chem over 50 years ago, can someone 'splain to me why we don't just mash at some temperature below 140F and allow an addition of amyloglucosidaise to hydrolize and convert all the starches into fermentable sugars? I suspect it may have to do with what sugars result from the conversion by specific enzymes (more glucose than maltose?), but would the proportion of different "toses" really make a difference? In other words, would it still be 'beer' if the larger proportion of simple sugars in the sweet wort wasn't maltose?

The literature is pretty thin on this topic. I'm planning to brew some light lagers and dry, crisp versions of Domestic and Continental ones as well when the weather turns a bit warmer and I can brew outside again. But I'm not looking to go "full Brut" again like I did last year. If anyone has experience mashing with gluco I'd like to know how long you rested the mash below 140F and how it affected your O.G. and flavor profile of the finished beer.

Brooo Brother

 

[Vale71]

Since I'm not a biochemist and haven't studied this topic since freshman Organic Chem over 50 years ago, can someone 'splain to me why we don't just mash at some temperature below 140F and allow an addition of amyloglucosidaise to hydrolize and convert all the starches into fermentable sugars?

One word: gelatinization temperature.
OK, that was two words, but you get the idea. Below gelatinization temperature not much can happen no matter how many enzymes you add to the mash.

 

[Robert65]

But gelatinization temperature is an amorphous and progressive thing, not a simple on/off switch. Likewise activation and denaturation temperatures of enzymes. Using a typical step mash, I normally see 75% of conversion before reaching what one would describe as gelatinization temperature of a particular lot of malt by standard definitions and analyses. There is plenty of available substrate, and activity of all enzymes, well below (and, for enzymes, even above) the temperatures homebrewers have been conditioned to accept as necessary.

 

[Brooothru]

One word: gelatinization temperature.
OK, that was two words, but you get the idea. Below gelatinization temperature not much can happen no matter how many enzymes you add to the mash.

Thanks for that pertinent reminder. Gelatinization was something I was maybe/probably aware of at some point but had long ago misplaced in my memory banks. So I jumped back down the Google Rabbit Hole to reacquaint myself with the topic. As always in such endeavors I discovered/rediscovered brewing knowledge to fill the sizable gaps and answer my questions. I really do appreciate the nudge in the proper direction.

So just to review with the class what I have learned today:

1). Gelatinization is necessary for the efficient breakdown of the starch molecules so the enzymes can convert it.

2). The starches in barley gelatinize between 136F-143F (rice, corn, wheat and other adjunct grain starches gelatinize at different temperatures).

3). Barley starch molecules come in two varieties, large and small, that actually have two different gelatinization temperatures. The variance in the proportion of large verses small starch granule distribution is affected by random factors like seasonal differences due to different growing conditions experienced from one year to the next. Typically the large molecules gelatinize in the 136F-143F range, but the small barley starch molecules don't gelatinize until 154F, which is also the mid-range temperature at which most adjunct grains' starch molecules gelatinize.

Number #3 (above) raises some interesting points. The first and most obvious conclusion is the efficacy of step mashes over single temperature mashes in maximizing conversion in the grist, especially when using adjunct grains. At a minimum, a 140ish rest would optimize the 'large' molecule barley starch conversion and a 154ish rest would optimize the small molecule barley (plus rice+corn+wheat) starch conversions.

The second conclusion is that those specific temperatures match the most active points of the beta amylase and alpha amylase enzymes in their respective ranges. Is that merely a happy coincidence, or is it a cause and effect?

The third conclusion is actually more of a still unanswered question of what role amyloglucosidaise plays during the mash. We know that it debranches the alpha 1,4 and 1,6 limit dextrins in the mash to make them available for conversion, but at what temperature range does this debranching occur? It has to be less than 140F since that is where gluco denatures. Would a rest at say 137ish F be beneficial since gelatinization of barley starches is occurring and beta amylase is becoming active at that temperature?

John Palmer talks about the mash temperature range of 113F-131F where proteolytic enzymes and beta-glucanase/cytase enzymes are active. Since most (barley) malts today are fully modified, a 'protein rest' in this temperature range is not considered beneficial since it can negatively affect body and head retention. Unless it is conducted in a narrower temperature band where beta-glucans are active but proteolytic enzymes are not, that is to say less than 113F. Once again, Palmer suggests a "pause" at 104F (93F-113F range) when doughing-in since this is when debranching enzymes are most active. 104F (40C) is also coincidentally the suggested temperature rest specified by George Fix as the first 'step' in a step mash.

Since switching from gas to electric brewing about six years ago I've been doing step mashes simply because I can. It's all automated, so why not? Now I can actually see a reason as to why. Mash-in and rest @ 104F for :15 minutes and let the amyloglucosidaise debranch alpha 1,4 and 1,6; rest @ 145F to let beta amylase work on large molecule barley starches; follow up at 155F for alpha amylase to likewise convert small molecule barley (plus corn+rice+wheat) starches; then slowly increase the temperature to mash out allowing as much starch as possible to be converted before the enzymes all denature.

I'm really getting stoked for warmer weather to try this with gluco in the mash to see if it has a favorable effect on yield and efficiency, and whether it results in drier, crisper lagers. C'mon, Springtime!

Brooo Brother