Wheat Beer Protein Rest

I'm a molecular biologist who recently got into brewing because it's a lot of what I like about science - pressure + beer. Anyhow, I've been really interested in grain enzymatic activity at mash temps (in that they're nowhere near germination temps) and came up with a practical hypothetical question.

From what I've read, barley beta-amylase is optimally active around 130F(ref), which is in range of a normal protein rest. That's not an issue when mashing barley because its starch gelatinization temperature is above 140F. However, the gelatinization temperature of wheat starch is around 125F(ref), meaning that at protein rest temps the wheat starch is actually available for conversion to the optimally active beta-amylase.

From a practical standpoint, if you are doing a 15-20 minute protein rest on a beer that is 60-70% wheat, should you mash shorter/hotter for the sac rest in order to maintain body and not dry it out like crazy? Or did I just come up with a problem that doesn't really exist?

For my hefeweizens I do a 15 minute "protein rest" at 122F, and then raise the temp to 150F for saccarification, and hold there for 60 minutes. My recipe is 50% wheat malt, 50% barley malt. I usually mash other (all-barley) ales at 152F for 60 minutes. I have not tested for starch conversion to see if I could cut down those times. However, I have not had a problem with overly dry wheats. My hefeweizens seem to have plenty of body for style. With the rest I get great "rocky" foam, absent with the all-barley beers. Hope this helps.

I guess I'm wondering if it's something that has been investigated before. It makes sense that you would get conversion of the wheat starches at protein rest temperatures, and probably at a higher rate than the typical infusion mash temps. Depending on the conversion potential during the protein rest and the proportion of wheat in your grain bill you could do some interesting things with the saccarification rest that you wouldn't be able to do with an all barley beer.

Then again, I'm too new at this to know what I'm talking about, so I could be totally wrong.

Well, beta-amylase can only cleave maltose off the ends of the larger molecules. Perhaps, especially at 130, alpha amylase is slow enough that there's not an appreciable increase in dryness in the finished product.

Beta-amylase can completely convert linear amylose, but it can't chew past the 1-6 linkages in amylopectin (the branch-points in the branchy starch molecule). From the sources I found, wheat starch is somewhere around 15% amylose with the rest being amylopectin. If you can imagine starting the sacc rest with >10% of your total conversion (.15 * 70% wheat grain bill) complete, you can see that there is potential for different mash techniques when using a high wheat grain bill and a protein rest that is not possible with a barley only beer.

Basically, the kinetics of the mash *have* to be different between the two scenarios but it's a question of whether it's different enough to allow for variations in technique. Maybe you can do something a little fancy with a high wheat mash, maybe you can't. I'm sure someone who is way more knowledgable has thought of it before and either they figured out that it doesn't matter, or there's an under-utilized wheat beer mashing technique floating around somewhere.

The attached is the profile that I have used for wheat beers for years. It is from Eric Warner's monograph in the AHA series. It makes a really nice beer and I adopted it so long ago that if I ever did try to figure out how it works I've long forgotten my conclusions. Note that there is a protein rest but the most interesting thing is that the decoctions are held at 160 °F. I guess this gives alpha amylase a chance to do its thing such that when returned to the main mash there are lots of reducing ends available to beta amylase.

Wow, ajdelange, you are a patient soul! Three and one half hours of mash time for a wheat beer is past the limits of my patience.

Lagers require triple decoctions so wheat is a short brew day.

So AJ, what kind of attenuation do you normally see with that mash schedule? It seems like you would get as close to 100% conversion as is possible. Also, does boiling for 20 minutes completely denature grain enzymes or can they refold after being brought back into the main mash (or are they just insanely stable)?

HIlife said:

Also, does boiling for 20 minutes completely denature grain enzymes or can they refold after being brought back into the main mash (or are they just insanely stable)?

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They denature...that's why he does the rest at 160--to convert before he denatures

ajdelange said:

Lagers require triple decoctions so wheat is a short brew day.

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hefe is the only beer i do dme instead of ag, so it's really short. 1.5 hours total :rockin:

HIlife said:

So AJ, what kind of attenuation do you normally see with that mash schedule? It seems like you would get as close to 100% conversion as is possible. Also, does boiling for 20 minutes completely denature grain enzymes or can they refold after being brought back into the main mash (or are they just insanely stable)?

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I don't have access to my records right now and I don't brew much wheat beer anymore either - sort of lost my taste for it but with the lagers which do not do the high temperature rest I usually get 75 - 78% ADF. But then you use the term 'conversion' so perhaps you are referring to mashing efficiency. I usually get 67 - 69% but that is measured a bit differently from what most people do. It is the ratio of effective extract in the keg to the total weight of the grain and thus includes all losses in the process.

Once the enzymes are boiled they are toast but the art of decoction mashing has us pull thick decoctions for the first 2 such that most of the enzymes are left behind with the main mash. There are enough in the decoctions to convert however- they do taste sweet after the rest.

I meant attenuation, the mash profile looks like it is tailor-made for converting the most possible fermentable sugars out of the grain based on all the available mash theory. Also, I did just look up heat inactivation of amylases and, while they are permanently inactivated by a 30 minute boil, they can re-fold after chemical or 85C heat denaturation.

Any enzyme that is maximally active at the ~70C range is a good candidate for a potentially highly thermostable molecule. That's the kind of temperature that only hot spring-dwelling thermophilic bacteria can survive in, which is decidedly not where wheat and barley like to germinate.

HIlife said:

I meant attenuation, the mash profile looks like it is tailor-made for converting the most possible fermentable sugars out of the grain based on all the available mash theory.

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Yes, it does. Warner's book may even have said something about that but as I said all my books are back in the States so I can't check. Home next week though.

It's worthy of note that these beers don't taste particularly dry to me - in fact somewhat sweet.

HIlife said:

I meant attenuation, the mash profile looks like it is tailor-made for converting the most possible fermentable sugars out of the grain based on all the available mash theory. Also, I did just look up heat inactivation of amylases and, while they are permanently inactivated by a 30 minute boil, they can re-fold after chemical or 85C heat denaturation.

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Interesting info about the refolding. Where did you find this? So far I have considered the amylases denatured permanently when inactivated by heat.

A.J.’s efficiency to our definition is around 85%. You simply need to divide by the potential extract of malt, which is generally around 80%. German brewers like to base their efficiency on the total grain weight and not just the potential extract weight.

Kai

Here's the paper I found on alpha amylase, it's an old biochemical paper and they are looking at B. subtilis alpha amylase but they talk about numerous previous reports of chemical denaturation and refolding as well as their findings on heat inactivation. Who knows if grain enzymes are more/less stable at high temperatures, especially within the context of the mash or decoction. If you boil thick vs thin mash I'm sure the conditions in the pot will be different and it's a matter of whether those conditions lend themselves to a more or less full unfolding of the enzymes.

A 30 minute boil will probably permanently inactivate everything. I'd bet that a ~10 minute boil would leave you with some activity from at least some of the different enzymes. Again, these temperatures are so far outside of biologically relevant temperatures that I am hesitant to apply general biological principles to the bag of enzymes that is the mash.