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A bit of background -- I brewed a pumpkin ale recently. The mash temp was maintained fairly high (well above 150F) for at least a full hour. The sparge was a disastrous 3-4 hour experience (despite lots of rice hulls!) The beer turned out fairly thin in body, leaving me to ponder my question here. My theory is that the mash dropped well into the range which favored beta amylase conversion for an extended period of time, allowing the complex sugars previously formed to be further reduced into fermentable sugars.

So my question is this: can beta amylase continue to produce fermentable sugars from the more complex sugars produced by alpha amylase?

My chemistry is rusty, but I certainly invite some technical explanations.

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Yes, at typical mash temperatures (ca. 150-156F), the beta amylase works in tandem with alpha amylase and limit dextrinase - the latter two enzymes reduce the number of limit dextrins, giving more opportunity for the beta to do it's work and produce a more fermentable wort.

Although your mash temperature was on the high side, there will still be some beta amylase activity, and so it could continue working when the mash temp was reduced. Although the optimimum temperature is in the 140-150F range, beta amylase isn't fully denatured until 160F, so it may not have been fully denatured by your high mash temp. It may be worth calibrating your thermometer also - 5F is not an uncommon error and yet makes a world of difference with the fairly tight tolerances of a mash schedule temperature.

The article below explains this in much more detail.

See

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When fly sparging, a mash out (raising the mash temp above 160, usually with an infusion of boiling water) is a good idea. Given the relatively long period of time between the end of the mash and the start of the boil, you want to deactivate the enzymes in the mash and "freeze" the sugars and dextrins in the desired ratios. Batch sparging is quicker and many brewers will skip the mash out when using this technique. –  Tobias Patton Oct 24 '12 at 14:19
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