Under a given set of conditions, there is an optimum cooking temperature and time to obtain the best quality of distillate and the best alcohol yield. I believe the question you have is about cooking small grains at high temperatures. There are a lot of ways to prepare grains for fermentation, but the simple goal of cooking is to gelatinize the starch granules, to make them available for hydrolysis by enzymes to convert to fermentable sugars but the complicated goal is to efficiently obtain proper gelatinization of starch, properly free up amino acids the yeast require, convert to fermentable sugars, reduce contamination and obtain a flavor extraction from the grains. The infusion mashing process we use, (simply cooking small grains at lower & proper temperatures), here at Wilderness Trail is designed around maximizing flavor first, energy second and time third.
You do not have to boil your grains up to 210F and you certainly do not want to cook any of your small grains (wheat, rye, barley, malted barley, etc) in that range, again you can but it will not be the highest quality distillate you can obtain in the end if you do that. You can cook corn to 210F and it doesn't do much more than waste energy cooking it that high, part of the high heat is to sterilize the grains of bacteria and you take care of that around 190F and you only need to cook corn around 190F-185F for proper gelatinization, we cook our corn at 190F, it saves energy from going higher, we convert all of the available sugars and sterilize our grains, that is why you do it. For wheat the actual gelatinization range is 136F-146F but we start adding our wheat around 155-160F. For Rye the actual range is 135F-158F and we add and cook our Rye no higher than 160F for good reasons. Our Malted barley never goes in higher than 145F to preserve the enzymatic activity and to keep the grains intact. Think of it this way, gelatinization is like popping popcorn under water, its a dramatic change in the grains composition.. and throw in some smaller ductile grains like wheat or rye and you blow them apart under the same conditions as well as a lot of protein you don't want to break down.
The reasons you do not cook grains beyond their proper gelatinization range is more about flavor than yield because if it is too rigorous, thermal decomposition of grain components will cause objectionable popcorn phenolic odors, yield is more impacted by poor grains, under cooking, poor conversion and yeast conditions. By using the infusion mashing process for small grains, you keep the branched chain amino acids and proteins in place with the grains that the yeast will use to properly make a flavorful result. If you boil your small grains, you are creating unbranched chain amino acids, degrading proteins and frankly blowing apart the flavor you are trying to extract. Small grains also get scorched very easy and there are Maillard effects that create all kinds of new chemicals from the high heat of small grains you don't want, plus why would you, the process doesn't require it. The yeast take these unbranched chain and Maillard effect's and turns them into higher alcohols (fusels) and other chemicals that alter the flavor and result of the beer & distillate.
In short summary for our whiskeys, we cook our corn to 190F and hold that for 40 minutes, we cool to 160F by adding some water additions of the overall mashbill and add our wheat or Rye and hold that for 30 minutes, we add more water additions to get to 145F which is when we add our Malted Barley which rest for 30 minutes. We add the rest of our water additions for our ferm set and the chiller takes it down to 90F. We send that to our fermenters, which are set to hold at 85F for three day beer and 78F for 4-5 day beer. By shortening the initial cook of the total water, your initial cook is thicker, for us that is around 18 beer gallons and that allows you to use less energy to heat up the initial cook and reserve the rest of the water for cooling capacity as well as when you add your grains you are also using that to help cool your mash down. For example I mentioned we add our wheat at 160F but after the grains are added the temperature drops to around 150F+ and rest out to a little above 145F.
We primarily make a wheated Bourbon but we also make a Rye Whiskey, which again even though the Rye will be the majority of grains, we still cook our smaller amount of Corn up to 190F and then cool it down to 160F before adding the majority of the mashbill of Rye. Infusion mashing is scientifically proven to offer a more flavorful distillate and smoother distillate, mainly for the reasons listed above.
Co-Founder, Master Distiller
Wilderness Trail Distillery