View Full Version : Extended discussion on starch conversion
Truman, I have enjoyed your occasional posts. Can I ask you what is (I think) a simple question?
Based on my historical readings, a full conversion could be obtained by mashing corn at about 150 F. I know the temperature would be adjusted for entry of rye and barley malt, but for corn, I understood that was the center of the range and if you went much higher you might create non-fermentable dextrins.
Yet I understand that modern batch cooking methods take corn mashes much higher than that, going say to about 100 Centigrade.
Where I am going wrong here? If higher heat levels are indeed used today than traditionally (1800's), why does that not cook the sugars and cause them to become unfermentable dextrins?
Many thanks for any information. I don't mean to highjack the thread and if this discussion should be placed elsewhere I'm in favour. Thanks all.
Wow, I am going to have to go to the books on this one. My first inclination is to answer that cooking the mash is to gelatanize the starch, not to convert it. The enzymes from the malt do the conversion. The cook is to get water into the tightly curled starch molecules. Dextrins are branched 1-4 bonded glucose molecules. They are not created by heat.
Modern mashes have gotten higher temperatures to gelatanize the more prolific amounts of starch in the newest breeds of corn. #2 Yellow Dent corn is bred/egineered to contain lots of starch for high alcohol yields per bushel. higher temperatures with water get faster gelatinization and better access for the enzymes.
When we batch the organic white corn we use for Rain Vodka, we use a different tepmperature for cooking because there is less starch and it is looser so we can use less heat (ie less$) and get the same results for gelling the starch particles.
Most interesting, thanks very much! I thought high temperatures may create dextrins but this seems not so. It seems like modern corn varieties need more heat to solubilize the starches and permit gelatinization. Thanks again for the info.
I thought high temperatures may create dextrins but this seems not so. It seems like modern corn varieties need more heat to solubilize the starches and permit gelatinization.
Perhaps you were thinking of mash temperatures, not cooking temperatures. A higher mash temperature favors the alpha amylase rather than beta amylase. The former breaks the starch chains into dextrins, while the latter breaks them further into simple, fermentable sugars.
This is a gross simplification - it's a complex mechanism that involves pH, Ca++ ions and others, amount of water, and so on, but temperature plays a major role.
In making beer, we generally mash from about 145F (63C) for a very fermentable wort to 158F (70C) for a less fermentable one. Of course, in making beer for distillation, unfermentable dextrins are unwanted as a waste of raw materials, so the mash is conducted as low as possible.
I think the answer is, by the time barley malt is added and conversion begins, the temperature is set low enough to preclude excess production of dextrins. However I am wondering too if higher temperatures during solubilization/gelatinization stage (for corn) affects in any way the flavor of the final ferment. If say at one time the mashing of corn was conducted at 150 F. (which I believe was the case) and now typically is conducted much higher (100 C if I am not mistaken) is there any reason to suppose the flavor of the mash and ferment would be different and if so how?
I believe "mash out" temperature is about 178 deg F.
This is the temperature at which the enzyme activities in mashing can no longer take place. Brewers often take the wort to this temperature at the end of the mash to prevent futher activity.
From what I understand, corn is boiled for some time prior to the mash, but I can't see how one could mash at boiling temp.
Well all these stages (boiling, solubilization, mashing) are part of a process. Here is a quote I found interesting from a late 1800's encyclopedia-type book called American Family Educator, available online through a quick search under this name and "whisky":
"The Manufacture of Whisky [the book uses the British spelling].
... The grain is mixed with malt and ground in a suitable mill and then run in a mash tub [note the grains are put in all together at once] where it is agitated with water at a temperature of 150 degrees Farenheit.
The Mashing Process
The mashing process is continued until the starch is changed entirely into malt sugar or maltose. This requires from one to five hours, according to the amount of grain in the mash. Malt contains a substance known as "diastase", which possesses a remarkable property of turning strach into maltose or malt sugar. It is for this reason that malt is added to the grain in the mash tub. Starch is changed by prolonged boiling into dextrin, which does not ferment readily, while maltose ferments very easily. Great care, therefore, must be taken during the mashing process that the dextrin formation is reduced, to a minimum. This is done by keeping the temperature near 150 degrees during the whole process".
Elsewhere I have read that too high a boiling of the corn can also caramelize sugars (which would reduce their fermentable principle) yet I understand again that modern batch cookers attain a high degree of heat, such as 100 C. But maybe the heating is not allowed to be prolonged. Anyway I am sure there is an explanation but I thought it was interesting that in the 1800's there seemed a focus on keeping mashing to about 150 F throughout all stages of the process.
If say at one time the mashing of corn was conducted at 150 F. (which I believe was the case) and now typically is conducted much higher (100 C if I am not mistaken)
I think you are confusing two distinct steps in the process - mashing and cooking. Perhaps this is because you know that when you make all malt beer (either distiller's beer, as in Scotland, or regular beer), there is no cooking involved. But when corn (maize) is used, as in American whiskeys, or corn or rice, as in traditional North American beers, they must be cooked.
In the distant past of American distilling, corn whiskey was made with malted (sprouted) corn that didn't require cooking, as the malting process makes the starches accessible to water, and the water soluble enzymes. And the Massachusetts pilgrims made ale with malted "Indian corn."
Unmalted corn has always been cooked (with a bit of malt called premalt), and typically this is done at boiling temperature or even higher using a pressure cooker. This is necessary because corn (or rice) starch molecules do not gelatinize at mash temperatures the way that malted barely starch does, or even unmalted barley, rye or wheat.
Corn starch gelatinizes at about 160-180F (70-80C), as I recall, and boiling does the job more quickly. Unmalted barley, rye and wheat gelatinize around 145-155F (63-68C). Malted barley starch is ready to go at a considerably cooler temperature.
So here is the procedure briefly (ignoring the addition of backset, the thing that makes it sourmash) - corn is boiled, cooled, rye or wheat is added, it is cooled a bit more, and the barley malt is added. This mash rests at about 145F (63C) for the starches to be converted to sugars by the malt enzymes, and is allowed to cool naturally to room temperature, when the yeast is added.
In just a bit more detail, the corn (and a bit of malt called premalt) is mixed with hot water to about 150F (65C) and then this is brought to a boil. This gelatinizes the starches - unravels the huge starch (amylopectin) starch molecules that contain thousands or tens of thousands of glucose units and exposes the interior to water. The malt is necessary to prevent retrogradation of this process (which is what happens when cornmeal or polenta thicken up as they cool and when bread stales).
This cooked corn is cooled to perhaps 156F (69C), and the rye or wheat are added. These small grains could also be boiled, but it takes extra energy and may impart a bitterness. After this is held a short time for the starches to gelatinize, it is cooled so that when the remaining barley malt is added, the temperature will stabilize at around 145F (63C).
Even this does not result in anywhere near 100% fermentable sugars, so some distilleries (I don't know how many - maybe all of them) add powerful enzymes either to the mash or fermenter to finish the job.
Hope this helps clear things up.
[I wrote my earlier post before checking back to see the two intervening posts from you and Roger.]
Here is a quote I found interesting from a late 1800's encyclopedia-type bookStarch is changed by prolonged boiling into dextrin, which does not ferment readily, while maltose ferments very easily. Great care, therefore, must be taken during the mashing process that the dextrin formation is reduced, to a minimum. This is done by keeping the temperature near 150 degrees during the whole process".
I think that it is not a good idea to depend on 19th Century non-scientific sources for authoritative chemistry. ;)
Elsewhere I have read that too high a boiling of the corn can also caramelize sugars (which would reduce their fermentable principle) yet I understand again that modern batch cookers attain a high degree of heat, such as 100 C.
I brew a pre-prohibition American pilsner in which I pressure cook corn grits (plus pre-malt) - about 22% of the total grain bill, at 15 psi/250F (121C/1 bar) for 20 minute plus cooldown. There is definitely some caramelization, which adds to the depth of flavor. Very nice, malty, caramelly, yummy flavors. But a trivial amount of the sugars are caramelized.
I don't know if these flavors would be carried over into a distillate, but I can only imagine that if they were, it would be a good thing.
I thought it was interesting that in the 1800's there seemed a focus on keeping mashing to about 150 F throughout all stages of the process.
To repeat what I wrote earlier, this is important in the mash itself (in order to preserve the heat-sensitive enzymes), but not the cooking prior to the mash.
Jeff, thanks for both posts! My only object here is both to understand the processes in question and try to figure out if what is done today was done the same way (more or less) 100 years ago, and if not, why not. I do understand the difference between cooking and mashing and the preliminary treatment corn needs to undergo if it is not malted. In effect, I am trying to figure out if the "cook" used to occur at 150 F. The quote I gave from the late 1800's book (admittedly a generalist text but quite detailed in some points) suggests to me this may have been the case. In other words, I understand the way things work today but that alone does not answer if they worked that way 100 years ago in American distilleries.
My understanding is corn gelatinises at 62-72 degrees C. or 144-162 degrees Farenheit (I do have a source for this and will dig it out). This being so, and since 150 F. is of course in that range, I am wondering if in fact one can cook corn at a steady 150 F. albeit this may take longer than if higher water/spent beer temperatures are used. Truman Cox indicated, and this makes sense to me, that modern corn varieties are higher in starch than earlier varieties and therefore high water temperatures assist to solubilise such modern varieties efficiently. But maybe with older varieties you could cook with lower heat and I thought the 1800's article I quoted gave some support for that.
For a table of gelatinization temperatures for different grains including corn/maize, see pg. 174 of the article by J.A. Morrison, "Production of Canadian Rye Whisky - The Whisky of the Prairies". This is a chaper of a distillery science text called "Alcohol" extracts of which are included at www.scocia.com by a person who studied at Heriot-Watt in Scotland (well-known school specialising in advanced studies in brewing and distillery science).
For a table of gelatinization temperatures for different grains including corn/maize, see pg. 174 of the article by J.A. Morrison, "Production of Canadian Rye Whisky - The Whisky of the Prairies". This is a chaper of a distillery science text called "Alcohol" extracts of which are included at www.scocia.com (http://www.scocia.com) ...
Thanks for that reference. I didn't find that chapter at that web site, but a search turned it up at http://distillers.tastylime.net/library/Listings2.htm, which looks like a great source for further reading.
I also found another interesting article called "The New Starches at http://www.foodproductdesign.com/archive/1998/0298CS.html. At the very end is a chart of gelatinization (or gelatinisation ;)) temperatures which also gives a similar range for corn as you have. But I suspect that this may not apply in practical cases. The chapter on the production of Canadian rye whisky says that even rye, with its lower gelatinization temperature, is raised to 85C and held for 10 minutes.
So while corn starch will gelatinize at lower temperatures than is commonly used in practice (after all, the baby corn plant makes it happen at ground temperature), it seems that boiling has been the practice for years. Check out a reference I have suggested before for brewing 100 years ago at http://hbd.org/aabg/wahl/. On page 705 (reproduced below) is a chart showing that gelatinization at 150F is "slow."
It is my feeling that boiling the corn has historically been the practice in brewing and distillation in North America. The high temperature and the mechanical agitation from boiling makes the process proceed quickly, and time is money. I wonder if your 19th Century source was speaking of all malted grain, or was perhaps not fully informed.
With modern breeds of corn and enzymes derived from Aspergillis mold and/or genetically engineered bacteria, lower temperatures are no doubt possible, and I am sure that the distillation industry is actively investigating it.
No question that gelatinization of corn proceeds at different tempos at different temperatures. The use of high temperatures today and no doubt for a long time in many distilleries can be put down I think to needs of efficiency (e.g. saving of energy), characteristics of modern corn, and the need to sterilise the mash to preclude the risk of subsequent bacterial contamination (Mr. Morrison discusses this latter point if I read him right). My original question was prompted by a statement on another board that an 1885 letter from Colonel Taylor stated that Frankfort distillers shared the practice of "mashing or cooking" the grain in "sour spent beer" (i.e., apparent 100% use of backset, interesting in itself) at a "lowly temperature". And I was trying to figure out what that temperature was as compared to modern cook and hold temperatures for corn. I posed the question here because we have a number of people with technical or specialist knowledge in the area.
My own conclusion from all I have read is that in the 1880's in Frankfort, KY pre-industrial methods had held on to the point of being defended by a leading industry figure. Whether these old methods produced a better-tasting (or worse-tasting?) white dog or bourbon than today, I cannot say, but I wished to shed some light on what seems an evident difference in the cooking and mashing process for corn from what exists today.
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