Tuesday, April 16, 2013

Mash Starch Test

I homebrew beer. I haven't talked about it much since February 2012 where I described the chest freezer I use to control fermentation and lagering temperatures.

Today I'm going to describe an experiment Sabrina and I did testing the effectiveness of my mashing procedure.

Mashing is the first step in making beer from malted barley and other grains. During the mash, you heat a mixture of crushed grain and water up to certain temperatures. You hold the temperature constant at one or many different points to allow the naturally occurring enzymes in the malt to convert starches into simpler sugars. Mashing usually involves holding temperatures for up to 90 minutes.

One method of testing the progress of this conversion is to perform an iodine starch test. A good description of what is going on can be found here. In brief, when an iodine solution is exposed to starch, the iodine changes color from dark brown to intense purple/black. Once all the long-chain starches are broken down, the iodine test will be negative. There will be no color change when the iodine solution is mixed with the wort. (Wort is the liquid sugar solution produced in the mash, or unfermented beer.)

The first experiment we did was to perform the iodine test every 10 to 15 minutes during a 90 minute mash rest. We also measured pH using test strips. We recorded time and temperature on the end of each test strip.  Here you can see the results:

The test was done by placing several drops of wort on a piece of chalk. A medicine dropper makes this much easier, just be sure to rinse it well between samples. Next, a couple drops of iodine solution were placed on the same piece of chalk. If you are careful to ensure that the iodine drops cover both part of the chalk soaked in wort and part of the dry chalk, it is very easy to detect if a subtle color change occurs.  You can see this effect rather clearly in the 80 minute and 90 minute samples above.

One thing I was not expecting was that once the iodine and wort evaporated from the chalk, the color disappeared. You can see how the color from the earlier samples is fading away. The color of the pH test strips also faded away as they dried.

I still had questions after this first experiment. All samples had been taken from the drain at the bottom of the mash container immediately after the mash had been stirred up.

The next time I made beer, we continued the experiment and collected more detailed data. This time we took samples from various locations in the mash, both with and without stirring. The pH was written down at each step so this time I have an accurate record of pH changes. Samples were taken every 15 minutes during a 60 minute mash.

The sample at the start of the mash was taken immediately after stirring together the water and grain. There was a clear purple color. 15 minutes later, three samples were tested. One from the drain without mixing or stirring (N), one at the top of the mash where the grain and water are mixed together (T), and one from the drain after mixing (M).

Without mixing, there was no reaction. This leads me to believe that the enzymes rather quickly convert the starches that are dissolved in solution. The top and mixed samples showed varying degrees of reaction. My conclusion is that at the top, starches continue to dissolve into the wort from the grain, and after stirring, these starches are distributed throughout the mixture.

The results from the rest of the mash were relatively unexciting. The reaction showed negative at 30, 45, and 60 minutes. This indicates that starch conversion finished rather early. A negative starch test doesn't necessarily mean that the mash was finished this early since the enzymes will continue to break down sugars. However, it is a good indication that the mash is progressing well.

A quick word on the iodine solution used for this. I bought 10% providone-iodine solution from the first aid section of my local pharmacy. I then diluted it 10 to 1 with rubbing alcohol. This lightens the color of the iodine so that the more subtle purple reaction can be seen. Otherwise the iodine is very dark and can mask a partially positive reaction.

I have heard that this test also works well using iodophor, a no-rinse sanitizer that is often used in homebrewing. Simply dilute the iodophor 10 to 1 with rubbing alcohol and it should work the same.

The Container Store sells some amber glass bottles with built-in medicine droppers that worked very well for storing and dispensing the iodine solution. It made it easier to avoid spills, which is important since iodine stains.

A couple months after I did my experiments, I ran across an episode of the Basic Brewing Radio podcast that goes into great detail on the subject. If you are interested, look for the March 3, 2011 episode.

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