Brewing Beer and the Starch Test

March 7, 2011

Making alcohol can be simplified as saying the yeast eats sugar and then converts it into alcohol and carbon dioxide. When making wine from fruit, the sugar is usually the form of fructose. But what about beer?

The “sugar” in the grain that makes beer is carbohydrates and starch. But in cider making, I said that I avoided starch because it doesn’t ferment, and I use an iodine test to make sure an apple is ripe and has therefore converted the starch to sugar.  Well, in beer making, they encourage the grain to start to sprout, which then allows an enzyme to convert the starch to a sugar the yeast can process.  The spouting is then stopped by drying or roasting the grain, leaving a product called malt that can be bought at any homebrew store.

The brewing process then begins in which the home brewer adds the malted grain to very warm water and let is soak/cook again to get the starches to convert further to complex sugars. And then what happens? My husband steals my iodine to test it to make sure the process finished and he doesn’t have any leftover starch!

A little bit of beer wort with a little bit of iodine. No starch here!

Remember, if you put iodine on something with a lot of starch, like a potato, it turns blue. In my husband’s test, it isn’t blue, so the starch to sugar conversion is complete and the next process in his homebrewing can begin.

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4 Responses to “Brewing Beer and the Starch Test”

  1. Erroll Says:

    I was with you right up until the end, “it is blue, so the starch to sugar conversion is complete …” ~ don’t you mean, “it is NOT blue?”

  2. Heather Says:

    You are right – thanks for the catch!


  3. […] step one is to find raw materials, such as grapes, fruit, grains, etc. with either sugars or complex carbs in them that can be fermented into a beer or wine in step two, which is legal. I know I was […]


  4. […] is spent grain? In order to make beer, grain is soaked to remove the sugars/carbohydrates, and then the water is removed leaving behind “spent grain.” This is now a by-product of making […]


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