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Old 07-24-2010, 02:07 AM   #1
JLem
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Default starch gelatinization question

A bit if history before the question...I am probably going to brew up a pumpkin ale this fall and after reading a lot of different recipes and advice I was curious as to whether pumpkin needed to first be gelatinized or if it could be added raw into the mash. I found a white paper on starch properties of winter squash and came to the conclusion that pumpkin starch gelatinizes at standard saccharification rest temps, which I believe means it can be added directly to the mash without any sort of pre-cooking. I decided to add this info into the growing body of the "everything you wanted to know about pumpkin beer" thread. In response to my post, passedpawn posted a chart of the gelatinization temps of various starches (page 21 of the aforementioned thread). Some back and forth ensued about whether or not anything special needed to be done with starches that had gelatinization temps lower than standard sacch. rests - i.e. whether or not they need to go through a cereal mash process. For example, according to the chart rye has a gelatinization range mostly under 60C. I had thought that cereal mashes were performed for those grains/starches that gelatinized at temps greater than standard mash temps. I was under the impression that for starch gelatinization you needed a certain minimum temperature, but now I am not so sure. On that same chart, for example, oats have a gelatinization temp mostly lower than typical mash temps and everything I've read about using oats says to use flaked/rolled oats because they are pre-gelatinized - otherwise you have to cereal mash them.

So, what's the deal with gelatinization temps and cereal mashes? Perhaps I don't truly understand a cereal mash - I thought it was just cooking (i.e. boiling) the grains to allow for starch gelatinization. However, this goes against what the chart is saying in terms of gelatinization temperatures. Can anyone shed some light on this?



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Old 07-24-2010, 12:43 PM   #2
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There needs to be a certain amount of time at the gelatinization temp to allow it to complete. Also, with the double mash/cereal mash procedure that brings the raw grains up to boiling temperature, you can use that to step up the temp of your main mash, kind of like a decoction.
Hopefully, this link works, if it doesn't , there's a graph on page 64 of The biotechnology of malting and brewing
By James S. Hough that shows the temperature profile, it can be viewed on Google Books.



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Old 07-25-2010, 12:35 PM   #3
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From my understanding of starch gelatinization, it is a physical/chemical reaction. I'm curious what is happening at higher temps that prevent the gelatinization process. It seems to me, given my admittedly limited understanding of chemistry, that if gelatinization can happen at 55oC then it should also happen at 65oC, maybe even at an accelerated rate. Unmalted grains like rye, barley, oats, and wheat all have gelatinization temperatures that are mostly below standard mash temps so what is happening, on a starch granule-level, when you put them into a standard mash? Why won't they gelatinize at those temps?

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Old 07-25-2010, 03:03 PM   #4
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Quote:
it is a physical/chemical reaction.
yes, it is. It still takes time for 100% completion.
Quote:
at 55oC then it should also happen at 65oC, maybe even at an accelerated rate.
Yes, it will. Even faster at 100 deg. Which is why the double mash schema ends with boiling. Same with cooking rice even for human consumption.
Quote:
Why won't they gelatinize at those temps?
It just may take more than an hour at mash temps. So why wait? Just boil it instead, or use flaked grains.
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