At the beginning of the brewing process, brewers combine hot water and crushed malted barley in a process called mashing. During the mash, enzymes naturally present in the malted barley convert starches into fermentable sugars.
Table of Contents
Boiled Down Summary
- Enzymes are protein catalysts that increase the rate of a specific chemical reaction by lowering the activation energy.
- Malted barley contains starch, typically composed of 20-30% amylose and 70-80% amylopectin.
- 𝛼-amylase, β-amylase, and limit dextrinase are enzymes naturally present in malted barley that convert starches to fermentable sugars in the mash.
- Brewers can control the mash conditions to achieve the desired sugar profile for the beer style they are brewing.
What are enzymes?
Enzymes are protein catalysts that increase the rate of a specific chemical reaction by lowering the activation energy. As catalysts, enzymes increase the reaction rate but are not consumed or permanently changed in the reaction (Cooper, 2000). This means they can catalyze a reaction over and over. Below is a short animation of how an enzyme catalyzes a reaction in its active site.
To learn more about enzyme basics, see this intro on Khan Academy.
Starch modifying enzymes in malted barley
Malted barley (malt) is a core brewing ingredient that contains starch, proteins (including enzymes), beta-glucans, polyphenols, and other compounds that affect beer properties. Brewers buy malt from maltsters who have taken the raw barley through the malting process. In the malting process, the inside of the barley kernel is modified to make it suitable for beer brewing. This modification includes the production of starch-modifying enzymes that brewers utilize in the mash.
Starch makes up roughly 65% of the weight of barley, of which 20-30% is amylose and 70-80% is amylopectin (Bamforth, 2006, p. 52). Amylose is composed of straight chains of glucose bound by 𝛼-1,4-glycosidic bonds. Amylopectin is made from 𝛼-1,4-glycosidically linked glucose chains branched by 𝛼-1,6-glycosidic linkages.
Brewers combine crushed malt (grist) with hot water in a process called mashing, where starches are converted into fermentable sugars and dextrins. During the mash, the starch in malt is first gelatinized, rupturing large starch granules into amorphous starch molecules (Kunze, 2019, p. 200). The released starches are converted to fermentable sugars and dextrins by the starch-modifying enzymes contained in malted barley: 𝛼-amylase, β-amylase, and limit dextrinase.
𝛼-amylase (alpha amylase)
𝛼-amylase cleaves 𝛼-1,4-glycosidic bonds in amylose and amylopectin at random points, shortening the chains. 𝛼-amylase has the highest activity in the mash between 70-74°C (158-165°F) and pH 5.6-5.8 and is denatured above 80°C (176°F) (Kunze, 2019, p.221). As 𝛼-amylase is randomly cleaving, it reduces the degree of polymerization of starches in the mash and causes a significant drop in the viscosity of the mash.
β-amylase (beta amylase)
β-amylase works from the non-reducing end of the starch and dextrin chains, releasing primarily maltose, although some glucose and maltotriose are also released (Kunze, 2019, p. 222). The optimum of β-amylase in the mash is between 59-63°C (138-145°F) and pH 5.4-5.5.
Limit Dextrinase
Limit dextrinase is a starch-debranching enzyme that cleaves 𝛼-1,6-glycosidic bonds in starch at branch points in amylopectin and the residual dextrins from amylopectin. The optimum activity for limit dextrinase in a mash is between 63-65°C (145-149°F) and pH 5.4-5.5 (Stenholm & Home, 1999).
| Enzyme | Optimal Mash Temp Range* | Optimal Mash pH Range* |
|---|---|---|
|
𝛼-Amylase (Alpha amylase) [1] |
70 - 74°C
(158 - 165°F)
|
5.6 - 5.8 |
|
β-amylase (Beta Amylase) [1]
|
59 - 63°C (138 - 145°F) |
5.4 - 5.5 |
|
Limit Dextrinase [2] |
63 - 65°C (145 - 149°F) |
5.4 - 5.5 |
[1] – (Kunze, 2019, pp. 221-222), [2] – (Stenholm & Home, 1999)
* Optimal temperature and pH ranges for typical mashes as expressed by referenced texts
NOTE: The rate at which enzymes catalyze reactions, called activity, in the mash depends on pH and temperature, but also many other factors like ionic strength, mash consistency, and more. The chart above is a good reference point for enzyme activity ranges, but specific optimums will depend on the exact conditions in a mash.
Measurement of starch modifying ability of enzymes
Starch-modifying enzymes were the first ever isolated enzyme preparations. In 1833, Payen and Persoz extracted enzymes (called a ferment at the time) from germinating barley and showed that they could convert starch to sugars (Armstrong, 1933). They called this separated ferment diastase, which we now know is a combination of various starch-modifying enzymes.
The term diastase lives on in an essential metric of malted barley that brewers rely on called diastatic power. Diastatic power measures the ability of all starch-modifying enzymes in malted barley to hydrolyze starch to sugars (Oliver, 2012, p.288). Maltsters provide the level of diastatic power of their malt on the certificate of analysis (COA) that they give to brewers.
In the United States, the standard unit of measurement for diastatic power is Lintner (°L), and in Europe, it is Windisch-Kolbach (WK), with a conversion of 1 WK = (°L*3.5)-16 (Mallett, 2014, p. 182). Some COAs will also specify 𝛼-amylase activity in addition to diastatic power.
Brewers control wort sugar profile with mash conditions
Brewers utilize temperature, pH, mash thickness, and other factors in the mash to control the starch-modifying enzymes (and other enzymes in the mash that are beyond the scope of this article), which impact the profile of the wort produced in the brewhouse.
Traditionally, many ale brewers used a single-temperature infusion mash. Lager brewers used decoction, where small portions of the mash were separated, boiled, and returned to the mash to raise the temperature (Bamforth, 2006, pp.65-66). However, most brewers today use a temperature-programmed mash that takes the mash through a series of temperatures using steam-jacketed vessels.
References
Armstrong, E. (1933). Enzymes: A Discovery and its Consequences. Nature, 131, 535-537.
Bamforth, C. W. (2006). Scientific Principles of Malting and Brewing. American Society of Brewing Chemists.
Cooper, G. (2000). The Cell: A Molecular Approach. Sinauer Associates. The Central Role of Enzymes as Biological Catalysts, https://www.ncbi.nlm.nih.gov/books/NBK9921/
Mallett, J. (2014). Malt: A Practical Guide from Field to Brewhouse. Brewers Publications.
Oliver, G. (2012). The Oxford Companion to Beer. Oxford University Press.
Stenholm, K., & Home, S. (1999). A New Approach to Limit Dextrinase and its Role in Mashing. Journal of the Institute of Brewing, 105(4), 205-210. https://doi.org/10.1002/j.2050-0416.1999.tb00020.x