Kolbach Index

When a brewer plans or executes a beer recipe, several parameters must be considered, from raw material values to equipment and process details. As?the malt is the main, when?not the only, source of sugar and other compounds to wort, the certificate of analysis (COA) must be often consulted. The Kolback index (KI) is not the only important parameter of COA, and?all certificate must be analyzed; however, this article will focus on this index. Before reading, please subscribe to this newsletter to receive a new article every week!

What is it?

When barley (or other grain)?is converted?into malt, proteins from the grain are broken into smaller fractions. In malting, the proteins are solubilized by endopeptidases and broken down by exopeptidases. The endopeptidases act in the middle of the chain and do not release free amino acids.

These small fractions?are easily solubilized?in wort during the mashing step. The Kolbach index is?obtained,?by?dividing the solubilized protein (or nitrogen) by total protein (S/T),?and represents?the proteolytic activity,?being?an important parameter to evaluate the malting quality.?

It is expected from a good malt, a KI?between?39 and 45 S/T, but these values can vary depending on the beer style to?be produced.

FAN

The Free Amino Nitrogen (FAN) is another COA parameter and?has a strong relation with?the Kolback Index.?The FAN measures how much nitrogen in the form of amino acids?is accessible from malt.?To have a healthy and complete fermentation, the yeasts require nitrogen for growing, requiring values between 150 and 250 ppm. The FAN analysis is critical, mainly in not-pure malt beer?because?the adjunct fraction will not provide FAN to the wort.

Despite the two parameters, FAN and Kolbach Index, involve proteins,?both must be analyzed?in every case; nonetheless, it?is expected?that a well-modified malt (good KI) also has good FAN levels.

Kolback Index in Practice

The evaluation of KI is an?important?criterion for deciding?do?or not?to do proteolytic rest. With low FAN malts or KI below 40 S/T, a rest at 50° for 5 to 15 minutes can help break down proteins, increasing FAN and low-weight proteins,?important?in the foaming process; however, making a proteolytic rest with KI higher than 45 S/T have?negative?effects, such as haziness, poor head retention, and dull malt flavors.

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