Enzymes for Brewers (V: Kinetics II, Temperature)


A graph of the Arrhenius equation (not to be confused with an Arrhenius plot).

This is another installment in the Enzymes for Brewers series. 

The rate of an enzymatic reaction increases with temperature. This is because the molecules in solution are traveling at a higher speed, lowering the average time it takes for them to collide. Back in 1889, the Dutch chemist Svante Arrhenius derived a simple equation that showed the effect of temperature on the rate of any chemical reaction. Basically, his equation predicts that the rate of any chemical reaction will increase exponentially with temperature. Experiments have shown that his equation is remarkably accurate for a wide range of chemical reactions.

In chemistry, a rough rule of thumb is that, for every 10 °C increase in temperature, the rate of a reaction doubles. This is only an approximation, and the exact rate of increase depends on a rate constant specific to each reaction. (A rate constant is just a number that describes how fast the reaction proceeds. It has to be measured for each specific reaction.) However, for a surprisingly wide number of “simple” chemical reactions, this rule of thumb is “close enough” for most practical purposes. If the reaction is actually a net reaction of a series of chemical reactions, or a cascading reaction, this approximation can be way off.

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Enzymes for Brewers (IV: Kinetics I — Substrate Concentration)


This is the fourth installment in the Enzymes for Brewers series. 


Biochemists envision enzyme-catalyzed reactions as occurring in two steps. First there’s the formation of the enzyme-substrate complex. Then there is the subsequent formation of the product.

In most realistic situations — and certainly in brewing — the concentration of the enzyme is small compared to that of the substrate. As the concentration of substrate rises, so does the reaction rate, as the average distance between enzyme and substrate is reduced. Put more simply, in a brewing-relevant example, the more starch there is in the mash, the more likely an amylase enzyme floating in the liquid is to bump into a strand of it. At some point, however, enzyme activity does not increase as all the enzyme is tied up in enzyme-substrate complexes.

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