Boiling effect on starch structure

[Owenbräu]

We read a lot about the effects of boiling on proteins as a result of a decoction, as well as the impacts of different temperature rests the decoctions have on the overall mash. Boiling forces the rupturing of cells, as well as denaturing the protein matrix where starches are stored inside the barley, thereby allowing them to be more easily gelatinize and subsequently broken down by enzymes.

Folks often use terms like free up, break up, burst, release and break down when describing what happens to starches during the decoction. What does this really mean, and how does boiling impact the structure of the actual starches?

In other words, does boiling actually alter the length, structure or form of the starches, or does it just make the big amylopectin and amylose reserves in the barley more soluble and accessible to enzymes? Can boiling break straight chains or alter branching points, thereby exposing more binding sites for saccharification enzymes?

[lhommedieu]

I admit to being out of my depth and may not be able to give you a correct answer to your question. However, what Kunze describes in Technology Brewing and Malting appears to be a physical change: whether or not his description merely forms the basis of your question is an issue to which to respond:

In hot aqueous solution a large amount of water is incorporated into the starch molecules. This results in an increase in volume which causes the closely packed starch granules to swell and finally to burst. The starch molecules lose their crystalline state and become more amorphous. An Increasingly viscous (sticky) solution is formed. (222) [Emphasis mine]

I think that it is fair to ask whether starch molecules subjected to high heat and constant agitation (boiling) are, in addition to swelling, effected by shearing forces that can change their structure. I was an English major in college; the last chemistry class that I took was back in high school, lol.

I haven't purchased deClerke's book yet. I'd be interested in hearing whether or not he addresses the issue.

[Bryan R]

I don't have the molecular answer for you, lhommedieu, explains its nicely. We call that "gels". You will see the decoction gel, when releasing all that new starch.

[Owenbräu]

Right, the mash thickens (like making oatmeal) as starches gelatinize. From there, the enzymes then liquify the mash (unlike oatmeal), which allows you to then boil it, hence the sacc rest during the decoction.

I suppose another way to infer this would be the difference in attenuation between a decoction mash and step infusion mash. If you did a 3 hr step infusion, hitting all the same times and steps as a decoction only you didn't boil the grains, would there be a difference in fermentability? If there is, then you know the boiling did something to the actual starches to allow enzymes to make a more fermentable wort.

I am curious if this has been done in a lab setting, measuring the % glucose, maltose, maltotriose, etc. afterwards.

[Bryan R]

Well the gel happens during boil. The sacc rest in the step allows you to convert the grains before the boil, otherwise you would lose out on all that extra sugar(depending on where you are in the main mash) of the decoction mash.

No, I think fermentabilty would stay the same. Decoctions are really not about the fermentability of wort, more so the extra extract from the same amount of grain, and the maillard reactions.

[Owenbräu]

Gelatinization occurs during the whole time you are heating the decoction. Thats why it gets thick, then turns to liquid once enzymes act on it. Once its liquid, you boil it to get those last stubborn starches to gelatinize.

If you release starches after the sacc rest (by boiling) and they carry over to be converted to fermentable sugars once returned to the main mash, then too should any starches gelatinized before you do the sacc rest during the decoction. I don't see why the sacc rest is necessary for dissolving starches. The only thing the sacc rest at 70C does is liquify the decoction and create a higher percentage of dextrins. Why not rest at 62-65C? If you didn't do the sacc rest, then you would actually have more unconverted starches to be broken down by beta amylase once returned to the main mash. You should actually get an increase in maltose production and fermentability by not doing the sacc rest during the decoction.

This is one part of the decoction process that never made sense to me, except to 1) reliquify the decoction so you do not scorch it, and 2) to salvage a medium-full body by creating a lot of dextrins at intervals along the way as you perform an hour protein rest on top of an hour maltose rest during the main mash .

[Bryan R]

Well, I think we are talking different things. I am not challenging gelatinization, I am talking about the "gel" in the boil. Here is the few pictures..
Before "gel"


"Gel"


Right, thats why I stated depending on where you where on the main mash. However, bringing sugars into the boil, along with the starches, aid in the malliards, and flavors of the boil.

[lhommedieu]

I thought that besides creating a maillard reaction (if desired) and boiling off protein gum, the boil allows you to return softer, gelled starch back to the main mash, so that Alpha can more easily break the starch down into fractions with reducing and non-reducing ends, and give Beta more non-reducing ends to turn into maltose?

Edit: Another way to look at is that while all starch will gell under heat, there are starches of different sizes present in the mash: starch that is in the form of flour will gelatinize more readily than larger pieces adhering to the inside the husks. One of the purposes of boiling after the first saccharification rest is therefore to cause those particles to swell and burst them apart; this action frees them from the husks, and returns more startch into the mash. Depending on the decoction method that is used, much of this starch will remain accessible to the enzymes responsible for breaking it down further into sugars.

When viewed in this manner "gelification" of the mash (the mash gets "sticky") is due to the introduction of more amorphous starch into the mash; Alpha now has more starch to play with, and so, consequently, does Beta, as it has more non-reducing ends available to convert glucose to maltose.

Of course, this begs the question, above, of whether boiling effects starch on both a molecular and physical level.

Edit: Finally, here's a part of a post by VladOfTrub over at HBT that helps to round out the picture:

"When you look at pictures of crushed grain, you'll notice chunks of white stuff. The chunks are hard starch. The starch is heat resistant and enzymes do very little to it. Even, when the grain is ground to powder, enzymes do very little to the starch. The powdered starch ends up in the bottle. The chunks contain the thing responsible for producing body and mouthfeel in beer. It is called amylopectin, which is slightly different in make up than amylose.

A few lines up, I mentioned that the mash will jell up when it is boiled. Boiling bursts the hard starch, releasing amylopectin. The amylopectin causes the mash to jell. When amylopectin forms, enzymes switch gears. They slow down.

During the several saccharification temperatures used throughout the process, Beta and Alpha will convert the amylopectin to A and B-limit dextrin. Limit dextrin creates body and mouthfeel in beer. Limit dextrin, although non-fermentable, should not be confused with non-fermentable sugar produced during single infusion, high temperature saccharification methods."

[Weizenberg]

Would this imply that an infusion mash starting at 64-65 Celsius would be preferable for mouthfeel? (By infusion we mean what you call a German step mash), as opposed to 62C.

I've seen people quote dough in temps as high as 66C for Bavarian Infusions.

[lhommedieu]

My qualified answer, given in the spirit that If I'm wrong I am, at least, working towards understanding:

I think that what you might infer from his comment, taken within the context of the conversation about jelled mash after decoction, is that a slightly higher mash (64-65C) will make starch slightly more soluble and give Beta more non-reducing ends to work on after Alpha has chomped on them,since Alpha is also slightly more active at this temp. This could produce more b-lmit dextrin and create better balance between a- and b-limit dextrin after Alpha creates a-limit dextrin at the next step - but after Beta is becoming denatured. In contrast, a single infusion mash done at a higher temperature that favors Alpha over Beta will produce a sweet beer that may seem cloying and unbalanced.

I am open to correction. After writing this I am reminded of a comment that a college professor wrote on a paper of mine (I can recall it to this day): "This is ingenious, but it is too, too bad that it is bad, perverse, wrong."