Friday, July 6, 2007

Brewing chemistry: Part 3- Mashing: Amylase

Once the barley has been malted and roasted, the grain is full of starch and enzymes. The grains are then dried and roasted. At his point, it is critical that the amylase enzymes not be denatured. Denaturation is any process that renders enzymes inactive. Heating (i.e. cooking) will denature proteins (enzymes are proteins). Roasting the barley too hot could destroy the critical enzymes. But, fear not, the folks who do the roasting know exactly what they are doing.

When the barley is roasted it is ready to be mashed. For extract brewers, this is something that isn't done. For all-grain brewers, mashing is a critical process. A screw up here and the whole batch could be ruined. Mashing essentially breaks up the starch into fermentable sugars. No sugar, no beer.

As I have mentioned before, I am now doing partial mashes (I'll post later about my method). In fact, all four batches featured recently were partial mash batches.

There are a lot of things that happen during a mash. I will focus on the action of amylase in the context of doing a partial mash.

During mashing, malted barley is heated in water. For partial mashing about 1 liter of water is used per pound of grain. The temperature control is critical since the amylase activity is dependent on temperature.

There are two main amylase enzymes at work. The enzymes are formed during the malting process thanks to the action of gibberillic acid. The two enzymes are alpha-amylase and beta-amylase.

They both break glycosidic bonds between the glucose molecules in starch. However, alpha-amylase does so randomly and beta-amylase starts at the end of the starch chain (the non-reducing end) and chops off two glucoses (maltose) at a time. The optimum temperature for alpha-amylase activity is around 158° F and that for beta-amylase is around 145° F. In all grain brewing temperature control is absolutely critical since the amylase activities must be balanced out. In partial mashing a temperature compromise is reached. At 152-154° F the activities of both enzymes are good enough to result in decent conversion.

The goal is to not convert all of the starch into glucose or maltose. Unless you are trying to brew a very dry beer with very low residual carbohydrate levels (i.e. T.A.L.L.). If beta-amylase activity is allowed to dominate, the result is a highly fermentable wort and a dry beer.

A great description of partial mashing is available on the BYO website

8 comments:

Anonymous said...

Are you sure you were talkin celsius not farenheit?

I´ll never understand how your country got as far as it did without metrical units (o.k., I admit it: I am not using kelvin in normal live either :-)

schinderhannes (from germany)

Chemgeek said...

Dang it!!!! Of course I meant °F and not °C. Force of habit as a scientist I guess. Everything I write is usually °C. Of course, I should have just converted to °C.

I would give anything to have the good ol' USA convert to the metric system. I really hate the American system. I love my country, but I could do without pints, quarts, gallons, ounces etc...

Anonymous said...

Apart from a nice pint of beer of course. I learned to love that in England, where a pint is a generous 568 ml. In comparison to the US pint (473ml) I prefer half a liter :-)

Schinderhannes

Anonymous said...

With all respect, the reason that "our Country" got as far as it did was because the "Mighty 8th"
Army Air Force measured their payloads in "Pounds" rather than "Kilograms". Remember, be nice the the USA, or we might bring Democracy to your country....

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Travis said...

Thanks for this article. It is very informative, especially with regards to the chemistry involved. I am studying Chemical Engineering and my final year project is actually to do with brewing (best course ever), so I was wondering if there are any more of your blog posts that deal with the chemistry of brewing (or any websites you can recommend). I am particularly interested in the fermentation process, as this is generally where most things can go wrong. Thanks again for the article and hope you can help.

Travis

Miko Castilo said...

Where can u buy alpha amylase at a cheap price as we r currently conducting a study using alpha amylase thank you so much sirs/maams

Miko Castilo said...

Where can u buy alpha amylase at a cheap price as we r currently conducting a study using alpha amylase thank you so much sirs/maams