Enzyme Conversion in the Mash
Mashing works because malted grain carries enzymes that break starch chains into sugars. In GF brewing, the amount and activity of those enzymes varies widely — and sometimes they are not enough on their own.
The two key enzymes in the mash are alpha-amylase and beta-amylase. They work together, attack starch chains in different ways, and have different temperature optima and heat tolerances. Understanding what each enzyme does — and when GF malts fall short — is the basis for designing a mash that converts fully.
Alpha-Amylase
Alpha-amylase is a random-endohydrolase: it attacks starch chains at random internal points, breaking large chains into smaller dextrins and some fermentable sugars. It is the enzyme responsible for liquefying the mash and producing the unfermentable dextrins that contribute body to finished beer.
Temperature range: Active from roughly 140–167°F (60–75°C). Optimal activity around 158–163°F (70–72°C). It survives into higher temperatures than beta-amylase.
At higher mash temperatures (155–162°F): Alpha-amylase dominates activity. More dextrins are produced, less complete fermentable sugar conversion. Beer body increases. Attenuation is lower.
Beta-Amylase
Beta-amylase is an exohydrolase: it attacks starch chains from the non-reducing end, cleaving off maltose units one at a time. Maltose is the primary fermentable sugar that yeast converts to alcohol and CO₂. Beta-amylase is responsible for most of the fermentability of the wort.
Temperature range: Active from roughly 130–155°F (54–68°C). Optimal activity around 140–149°F (60–65°C). It is thermolabile — it denatures rapidly above 158°F (70°C).
At lower mash temperatures (148–153°F): Beta-amylase is more active longer before denaturing. More maltose is produced. Beer is drier and more fermentable. Less body.
The practical dial: lower mash temperature = drier, more fermentable wort. Higher mash temperature = fuller body, less attenuation. Both enzymes are always active across the mash temperature range; the ratio of their activity shifts with temperature.
Diastatic Power in GF Malts
Diastatic power (DP) is the measure of a malt's total enzyme activity — how capable it is of converting its own starch and any unmalted adjuncts added to the mash. It is expressed in degrees Lintner (°L) in the US or Windisch-Kolbach units (°WK) in Europe.
Barley pale malt typically carries 100–160°L — well above the 35°L threshold generally considered the minimum for self-conversion of a simple grain bill.
GF malts vary considerably:
- Malted millet: typically 80–120°L depending on cultivar and malting quality — comparable to barley, the best performing GF base malt
- Malted sorghum: typically 40–80°L — adequate for self-conversion of a sorghum-only bill but leaves less margin for adjunct conversion
- Buckwheat: near zero DP — no useful enzyme activity, cannot self-convert
- Rice: near zero DP — must be converted entirely by base malt enzymes or exogenous additions
- Oats: very low DP — similar to rice
A mash with a large adjunct fraction (30–50% rice, for example) requires the base malt to carry enough DP to convert both its own starch and the adjunct starch. Marginal DP situations — particularly sorghum bills with significant adjunct additions — are a leading cause of incomplete GF mash conversion.
Exogenous Enzymes
When endogenous DP is insufficient, exogenous (externally added) enzyme preparations can close the gap. For GF commercial production — and for homebrewers using sorghum as a primary base grain — specific enzyme products are well established in the industry.
Thermostable vs. Fungal Alpha-Amylase: The Critical Distinction
Not all alpha-amylase preparations operate at the same temperature, and this distinction is essential for sorghum brewing.
Termamyl SC DS (Novozymes) is a thermostable bacterial alpha-amylase derived from Bacillus licheniformis. It remains active up to approximately 200°F (93°C). In a step-mash or in-vessel gelatinization program where the mash is raised to 185–190°F to gelatinize sorghum starch, Termamyl is the enzyme that can be added at that high-temperature stage — it liquefies starch as it gelatinizes. Typical dosing in commercial GF production: added at mash-in and retained through the high-temperature step.
Fungamyl 800L (Novozymes) is a fungal alpha-amylase derived from Aspergillus oryzae. It has excellent saccharification activity and produces well-fermentable wort, but it denatures above approximately 160°F (71°C). In a sorghum step program, Fungamyl is not added during the high-temperature gelatinization hold — it is added after the mash has cooled back into the saccharification range (130–155°F). The two enzymes are therefore stacked in sequence rather than added simultaneously.
Ondea Pro (Novozymes) is a combined enzyme preparation designed specifically for high-adjunct sorghum recipes. It contains alpha-amylase, beta-amylase, pullulanase (a debranching enzyme that improves fermentability by attacking starch branch points), and protease activities in a single product. Dosing guidance from the Novozymes Brewing Handbook (2013): 1.2–2.2 kg per ton of grain for sorghum-dominant bills up to 100% sorghum.
Other Commercial Enzyme Preparations
Glucoamylase (amyloglucosidase): Cleaves glucose from the ends of dextrin chains, converting unfermentable dextrins into fermentable glucose. Used for very high-attenuation or dry-style GF beers. It continues working during fermentation when added to the fermenter. Attenuzyme Pro (Novozymes): dosing scales with how dry you want the finished beer — generally 0.05–0.10 kg per ton of grain per additional percentage point of attenuation targeted.
Beta-glucanase: Breaks down high-molecular-weight beta-glucans responsible for wort viscosity. Critical for millet-heavy bills or any GF grain bill where vorlauf flow is sluggish. Ultraflo Max (Novozymes): 0.10–0.15 kg per ton of grain. Effective at 95–113°F (35–45°C); add during the beta-glucan rest if using a step program.
Amylase blends: Some commercial preparations combine multiple activities. Follow supplier dosing guidelines — over-dosing glucoamylase in particular produces a thin, watery beer with no body.
Exogenous enzymes are not a substitute for good malt selection and mash design — they are a tool for specific situations, particularly adjunct-heavy commercial GF production.
Enzyme conversion failures:
- Using sorghum with marginal DP for an adjunct-heavy bill — insufficient enzyme activity for complete conversion
- Mash temperature too high early in the mash — denaturing beta-amylase before it can produce fermentable sugars
- pH outside the 5.2–5.4 range — both enzymes have reduced activity outside this window
- Incomplete gelatinization of high-temp grains (sorghum, corn, rice) — starch that isn't gelatinized cannot be converted by amylase regardless of DP
Signs of successful enzyme conversion:
- Iodine test returns amber/clear on spent grain sample — no unconverted starch
- Pre-boil gravity hits expected target within ±2 points
- Wort ferments cleanly to expected final gravity
- No residual starchy haze in finished beer
Source Notes
Alpha and beta amylase activity ranges from brewing science literature. Diastatic power values for GF malts from malting quality reports and commercial brewing trials. Exogenous enzyme product details and dosing guidance from Novozymes Brewing Handbook (2013) and commercial GF production documentation.