Why Malt the Barley for Beer?


Dear Reader, usually the deal here on Aard is that I tell you what to think and you reply, zombielike, “Yes… Master… Kill… Kill…”. But today, let’s turn the tables. I’m going to ask a question about a simple scientific-culinary matter that has baffled me for decades. And I hope someone out there knows enough about yeast to enlighten me.

  1. When starved of oxygen, yeast turns sugar into alcohol.
  2. When germinated, barley grains, by means of the enzyme amylase, turn some of their constituent starch into sugar. This process is called malting.
  3. In order to make beer, you must malt the barley. This suggests that yeast cannot make alcohol out of starch.
  4. But Swedish vodka is made from potatoes, which are very high in starch but cannot be malted. This suggests that yeast can make alcohol out of starch.

So here’s my question: if yeast can make alcohol directly out of starch, why bother malting the barley before making beer? Couldn’t you just mix barley flour with water and yeast and put a lid on the slop?

Update same evening: Dale P and other Dear Readers solved the conundrum för me. Yeast cannot in fact ferment starch. To ferment potato mash, you add enzyme-containing barley malt to it!

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21 thoughts on “Why Malt the Barley for Beer?

  1. I did some quick digging on the interwebs and found two tidbits for you…

    “…germination creates enzymes which are required to convert starch to fermentable sugar later in the brewing process…” from http://www.leeners.com/beer-about-barley.html


    “…Malting is a process of bringing grain to its highest point of possible soluble starch content… It is at this point that the seed is rich in the starch it needs to use as food for growth.” from http://www.alabev.com/ingredie.htm

    So it’s either to generate enzymes, or make more of the barley’s starch soluble. Or both (I’m suspecting both).


  2. Potato starch still requires conversion to sugar for fermentation to occur. Typically, this is a thermal conversion by a long cooking step, rather than an enzymatic conversion as takes place in barley malt. It’s worth noting that in beermaking, the partial conversion during malting is taken to completion during the brewing process (mashing). Potato vodka skips the malting stage, but still requires the mash step to hydrolyze the starch into fermentable sugars.

    So no, you can’t just ferment a pot of barley flour – you could heat it, and get some fermentable sugar out of it, but it’d be inefficient. Since vodka is a distilled spirit, inefficiency can be compensated for by the distillation process.


  3. From

    “2. Cook the potatoes. Place the potato cubes into the pressure cooker. Then, pour water over them until the potatoes are completely covered, plus about an inch of water. … Cook until the potatoes have completely combined with the water, or the potatoes have nearly liquefied.
    “4. Add malt or enzymes. Wait until your potatoes have cooled to about 150 degrees before adding malt or enzymes. The malt converts the starch in potatoes to fermentable sugars.’


  4. Amylase is amylase, for the most part. In Chicha production, it’s human saliva that provides the amylase to break down cassava starch. And yes, thermal hydrolysis is a way of breaking down starch into fermentable sugars, but it’s reasonably energy-intensive and requires high heat and pressure to be efficient compared to enzymatic hydrolysis.


  5. When baking sourdough bread, a common technique is to proof your dough in the fridge overnight. This slows down the yeast activity, while leaving the amylase enzymes free reins converting the starch. As the dough is removed from the fridge, the yeast wakes up and starts feasting on the resulting sugars.

    I believe that the addition of malted barley to the dough has a similar effect, but saves you time, probably at the expense of flavours.

    Not sure if this has anything to do with anything, really. Your #3, perhaps.


  6. Nope,

    Yeast cannot ferment starch, they only take in simple sugars (glucose, fructose, maltose, etc). In making beer or vodka, the first step is to convert the starch to sugars via enzymes. Traditionally in European production malted barley was the source of the enzymes.

    When barley germinates (the first step in malting) it starts producing large quantities of amylases (there are several kinds) and other enzymes that together breakdown starch. Total starch & starch breakdown products don’t increase. The heating step that follows kills off one set of enzymes but leaves others working. It also adds flavor.

    Boiling potatoes doesn’t break down starch. It does melt starch crystals so they are more easily digested by the enzymes

    Brought to you by a Certified Biochemist!



  7. As always, oxygen is as much of a killer as it is an enabler. Oxygen will kill the enzymes given half a chance, but they can survive with the help of enough sugar to feed the engines as it were. In order to make fermented brews with Stone Age technology which could not be completely anaerobic you needed a lot more sugar than you do with modern or even historical technologies. Malting and adding sugar in the form of honey helped a lot.


  8. Another, and important reason, for malting the barely is by maximizing the starch –> sugar process, you can get a greater diversity of flavour when you roast the malted barley, which is why you can brew very light lagers up to very dark stouts from the same two row malted barley – roast it longer to caramelize the sugars more.


  9. Martin: I am glad to see that you have been enlightened on the core question (starch needs to be broken up into its constituent sugars for these to be available for fermentation, and using enzymes is the most efficient way to do this).

    However, I have a nit to pick, which may enlighten you further:

    But Swedish vodka is made from potatoes

    While that is true for many Swedish vodkas, it is not always so. Absolut, for example, is a grain vodka.



  10. When germinated, barley grains, by means of the enzyme amylase, turn some of their constituent starch into sugar. This process is called malting.

    But then what is malted milk, as in malted milk balls? Surely the milk is not germinated? And milk has very little starch to be turned into sugar.


  11. Some starches seem to split easily – eg mescal is made by cooking cactus in a pit, then fermenting (then distilling) according to a winemaker friend of mine who watched the process in rural Mexico. Also, I often wonder what “sour mash” is about. Can any biochemist out there say if cooking up starch which has been acidified with organic acid products of bacterial fermentations (eg sourdough) can produce a worthwhile yield of fermentable sugar? Might rye starch be more amenable to to hydrolysis by this method (if it is a method)?

    (As an aside, Sake is made using Aspergillus mold to split rice starch, and mineral acids also split starch)


  12. Mescal and tequila are made from agave which is rich in fructo-oligosaccharides, not starch.

    The agave is heated at ~75C for up to 36 hours. You can heat at higher temperature for shorter time, I have seen retorts used (~121 C). I’ve also read of low temperature processing that uses natural enzymes … but I know little about this process.

    You can make corn syrup from corn starch by adding hydrochloric acid and retorting. Corn syrup includes dextrose, maltose and oligosaccharides at different levels, depending on the time-temp-acid level. Only dextrose and maltose are fermentable (by distillers yeast), so an acid hydrolysis is inefficient compared to enzymatic. It is much more expensive from an energy standpoint too.

    Sour mash Bourbon process adds material from an earlier mash to the current one – this drops the pH and makes the environment less hospitable for bacteria or other spoilage organisms, which could affect the flavor and fermentable sugar yield.

    As far as I know, malted barley or malted wheat are added to potatoes for potato vodka for the mashing step. Potatoes would be cooked thoroughly before adding the malt to gelatinize (solubilize) the potato starch. You could, theoretically, add glucoamylase directly or even grow koji mold on the potatoes, but I’ve never heard of potato vodka made that way.


  13. #10 is wrong. Oxygen does absolutely not kill amylase enzymes. It IS bad for beer in/after the fermenting process however. The problem in malting for the most part in preserving these are in the kilning process. They are extremely susceptible to heat, especially with moisture present, which is why we give a low temperature “free dry” before raising the temp for a roast to give color and taste. The more the roast, the less enzymes, therefore less (to none in many dark malt examples) conversion of starches to fermentable sugars. This is why a light pale malt is the base of ALL beers (alcoholic anyhow). And the same rules apply for distillation, this is just an added process to concentrate.


  14. “Update same evening: Dale P and other Dear Readers solved the conundrum för me. Yeast cannot in fact ferment starch. To ferment potato mash, you add enzyme-containing barley malt to it!”

    Just wondering about fermentation, is it the same with fermenting alcohol/beer or fermenting foods like fermenting vegetables? I’m interested in fermentation co’z it’s so healthy according to this article


  15. Two different kinds of microbe are involved. Single-cell fungi (yeast) make the alcohol and carbon oxide in beer. Lactic acid bacteria ferment i.e. cabbage into Sauerkraut and kimchi, and make sour dough. Both processes are known as fermentation.


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