Conversion of Starch to Sugar

The process of converting starch to sugar occurs in the mash tun. The mash tun is the first vessel in the brewing process where grain and adjuncts are mixed with water. Examples of adjuncts are wheat, corn, and rice. The mixture of grain with water is called the mash.

After mixing all the grain and water together to form the mash, the mash must be raised to a temperature range between 150-168 degrees F called the brewer's window. This is acheived by a burner run off gas below the mash tun or steam that runs through jackets around the mash tun. Alternatively, mixing 172-74 degree water with the colder grain usually results in the mash falling into the brewers window (this is more risky to do). It is less risky to start at an temperature in the 140's after all grain is mixed and then raise the temperatue gradually to your mashing temperature using a heating method mentioned above.

This is the most critical part of the brewing process because at this temperature range the starch in the grain and adjuncts is converted to sugar by two enzymes. WIthout sugar, there is no beer!! If the temperature exceeds 168, the enzymes will be denatured and no starch will be converted to sugar. If the temperature is too low, the enzymes will not be activated and no starch will be converted. Two enzymes alpha amylase and beta amylase are responsible for this conversion.

Once the mashing temperature is reached, the mash is kept at this temperature anywhere from 20 minutes to 2 hours depending on the mash temperature and the mash tun. This allows ample time for the enzymes to convert all the starch to sugar. To test for a complete converstion, a sample of the mash is taken and a drop of iodine is applied to the mash. If the iodine turns yellowish or clear, all starch is converted. If the iodine remains dark, all starch is not converted and a longer resting time period at the mash temperature will be needed to convert the rest of the starch.

Why is this important? The yeast is eventually responsible for converting the sugar to alcohol (ethanol). Yeast is uncapable of metabolizing starch or complicated sugars (carbon chains). With simple sugars like glucose, fructose, malto-triose, and triose produced during mashing, the yeast is able to metabolize thesee simple sugars, reproduce, grow, and produce the ethanol that is responsible for getting us drunk. I will talk further about the brewer's window and the difference between mashing at lower or higher temperatures in this window. Some Otter Creek Porter is calling my name, so I have to go.

Time to drink some good beer,
Brian