Monday, March 19, 2007

Brewing chemistry: Part 2- Kilning

Once the barley has been malted, and the barley has just started to sprout, the next step is to kiln dry the grain. In some cases, the grain is roasted.

The purpose of the kilning (if that is a word) is to dry the grain, but also, in some cases, to roast it.

During the heating, some enzymes become denatured. However, most of the amylase enzymes survive. These will be utilized during mashing to liberate fermentable sugars from starch. Fortunately, during the drying phase, most lipase and lipoxygenase enzymes are destroyed. These enzymes are implicated in the formation of off flavors in beer as it ages.

A second goal of kilning, in some cases, is to roast the grain. Pale malt is typically not roasted, whereas, roasted barley is (umm, that's why they call it 'roasted' barley). During the roasting process a glorious reaction called the Maillard reaction occurs.

The Maillard reaction is a general reaction between an amino acid and a reducing sugar. Considering there are a lot of types of sugars and amino acids available, the Maillard reaction can form a variety of products. The Maillard reaction is a very important reaction in food chemistry. The products contribute to the color and flavor of browned bread, chocolate, seared meat, caramel and deep-fried death. Now, I'm not a food chemist. I'm just a chemist who likes food. My understanding is the Maillard reaction is central to what food chemist study. The following is my understanding of the Maillard reaction.

In the first step, an amino acid reacts with a reducing sugar (glucose is shown) to make an amino glucose. This part of the reaction is known as the Amadori reaction.



The Amadori complex can react with dicarbonyl compounds in a reaction known as the Strecker degradation. This results in a number of aldehydes such as, isobutyraldehyde and furfural and others. Some examples include:



Another important product of this breakdown are the melanoidins. This class of poorly characterized heterocycles contribute a dark color and a toasty aroma.

In reality, the Maillard reaction is more important during the boiling of the wort (a future post), but it does play a role in the roasting of grain.

UPDATE:
Try #2 for the images. I don't know why, but my images stopped appearing. I reloaded them above as .gif files and below as a .bmp file. Can you see it?

7 comments:

Matt Jenks said...

I was thinking of the Maillard reaction over the weekend as it pertains to our deliciously brewed beverages. My wife bought me a gallon of stout when she went to Winston-Salem early last week, and I was enjoying it with my Irish dinner on Saturday.

In short, I peered into the glass and wondered which chemical lent their light-absorbing properties to the brew to provide such a luscious, beautiful dark color. I pondered the Maillard reaction and maltose for a while. That's the kind of dork I am.

Chemgeek said...

Embrace your dorkhood! and embrace your wife. A gallon of stout? Oh my!! What a wife!!!

Lab Cat said...

I can't see your images :(

Matt Jenks said...

Too much embracing of the stout and then embracing of the wife will put me squarely into the "third child's a charm" boat.

Chemgeek said...

Lab Cat, I have no idea why you can't see them. I'll try posting them in a different format when I get home tonight.

Matt, your preachin' to the choir.... As we say up here in the North Central: uff da!!!!

Matt Jenks said...

Uff Da!!! is such a good beer.

I couldn't see them, either, but it seems to be fixed now.

Anonymous said...

Hi,
Your last post was a while ago, so I'm not sure if you're still running this blog, but it's worth a try. I'm finding this site really useful at helping with the chemical side of brewing, but you only reuploaded one of the two pictures of the Maillard reaction. Would it be possible for you to upload the second?