This is the final installment of the Enzymes for Brewers series.
A ribbon model of beta amylase from barley.
Barley seed can sprout at temperatures as low as 34 °F (1.1 °C). The seedlings can survive overwinter at temperatures below freezing, although the plant does not grow at these temperatures. So, the enzymes in barley are active as low as 34 °F (1.1 °C). The amylase enzymes we use in brewing slowly turn the starch in this seed into sugar, which is used as fuel for germination and early growth. Eventually, the first leaf unfurls, and photosynthesis begins supplying the plant with sugar as the starch stores in the seed are depleted.
Temperatures in Brewing
In brewing, we utilize barley enzymes at temperatures far above that which would kill the living plant. We mash at high temperatures so that the enzymatically-catalyzed reactions occur quickly. (If a barley seed converted all it starches to sugars within an hour, the plant would quickly be infected by soil bacteria and die. In situ, this takes weeks.)
As far as starch conversion is concerned, we could, hypothetically, mash at just about any temperature. For example, if we use the 10 °C approximation of enzyme rate, and we discover that a 30-minute mash at 158 °F (70 °C) can yield a negative iodine test, then a 60-minute mash should be able to do the same thing at 140 °F (60 °C). Furthermore, a 120-minute mash at 122 °F (50 °C) should accomplish the same thing. The numbers may not be exactly right, but you can see that, at lower temperature, exponentially longer mash times are required. Of course, at lower temperatures, the activity of other enzymes — and, for very long rests, the growth of lactic acid bacteria — would interfere with the goal of producing quality beer. More importantly, the activity of the amylase enzyme on starch changes when the starch is above or below it’s gelatinization point. Some starch degradation can occur below its gelatinization temperature. (In living barley, all starch degradation occurs below the starch’s gelatinization temperature.) Interestingly, one study found that a 2-hour mash at 131 °F (55 °C) — below the temperature at which most barley starch is gelatinized — was able to extract 90% of the fermentable sugars from the malt.
Enzyme Activity in a Single Infusion Mash
In a single infusion mash, in the usual range (148–158 °F/64–70 °C), the concentration of beta amylase declines steadily throughout the rest. However, enough of the enzyme remains active for long enough that sufficient maltose production can be completed. Significant declines in the population of alpha-amylase molecules is not seen unless the temperature is near the high-end of this range. Even then, it’s rate of decline is slower than that of beta amylase. When a mashout is employed, the rate destruction of the enzymes increases. Levels of beta amylase decline to zero (or nearly so), but some alpha amylase activity can persist (perhaps even into the boil).
Although above the traditional range for a protein rest, a small (but measurable) amount of protein degradation occurs in a single infusion mash. (With modern, fully-modified malts, the end of a single infusion mash should leave the levels of starches, sugars, proteins, and gum in their optimal range.)
Enzyme Activity in a Step Mash
In a step mash, the 113–131 °F (45–55 °C) range was traditionally called the protein rest. (And sometimes this rest was broken up into two ranges, a lower range for peptidases and a higher range for proteinases.) If you are mashing undermodified malt, a rest in this range will result in a significant degradation of proteins. This is also the optimal range for beta glucanase. If phytase was present in your malt, it will also be active at this range, although it is above that enzymes usual stated range (95–113 °F/35–45 °C). It will, however, be progressively destroyed and will not survive the next increase in mash temperature. (Also, the effect it has on your mash will be minimal, as phytase requires a long rest to produce sufficient acid to lower the mash pH.) In the protein rest range, the amylase enzymes will already be working, producing a significant amount of fermentable extract after 15–20 minutes.
Many times, the next rest in a step mash is in the 140–145 °F (60–63 °C) range. This is frequently described as being an optimal range for beta amylase (and it is, in terms of activity). During the ramp up to this temperature, the denaturation of beta-amylase will already have started. However, for a rest of a reasonable length, sufficient beta amylase will remain to do its job in the traditional saccharification range. In the optimal beta-amylase range, alpha-amylase is active, however at a lower rate than it will be during the final rest. Small but measurable amounts of protein degradation occur at this rest also, and will continue into the final rest.
The final rest, before a mash out, in a step mash proceeds much as a single infusion rest. However, less beta amylase is present at the beginning as some of it has been “used up” in the earlier low-temperature rest. Still, some beta amylase activity may persist until 90 minutes into a step mash. (Exactly how long it lasts depends on the mash thickness and the exact temperature changes.) Some alpha-amylase activity can continue past the two hour mark, even following a mash out. Protein degradation still occurs at this rest, although it’s rate is greatly slowed.
The results of brewing science experiments are sometimes contradictory. Laboratory mashes frequently behave different than real-world brewery mashes. Likewise, different studies of the behaviors of enzymes in the mash have occurred at different mash thicknesses, with different grists, and different temperature programs. So, the information here will likely not hold in any and all situations. However, learning about the basics of how enzymes work the mash may help in some situations. For example, if you mash in at too low of a temperature, you should understand that you can take your time (within reason) heating the mash up to its correct temperature. Conversely, if you mash in too high, you should work to get the mash temperature down more quickly. This will avoid undue denaturation of enzymes (especially beta amylase). Simply mashing in too high, however, will not instantly destroy all the enzymes in the mash.
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