Skip to main content

The Sugar Bible: Wort Sugars, Enzymes, and Fermentability

The mash does not make "sugar." It makes a specific mix of sugars, and that mix decides how the beer ferments, how it finishes, and how it feels in the glass. Enzyme choice is sugar-profile choice.

Never thought about what kind of sugar is in wort? Here is the whole idea in one breath: starch is a long chain of glucose units, enzymes are scissors, and where the scissors cut decides what the yeast gets to eat. Cut the chain into single units and you get one kind of beer. Cut it into pairs and you get another. Leave some chains long and the beer keeps body. Everything else on this page is detail around that one idea.

Sugar 101: it is all chains​

Every sugar that matters in brewing is built from the same brick — glucose — in chains of different lengths:

NameSizeYeast can ferment it?
Glucose1 unitYes — first and fastest
Maltose2 unitsYes — the workhorse of normal beer wort
Maltotriose3 unitsPartially — depends on the yeast strain
Dextrins4 to dozens of unitsNo — they stay in the beer as body
Starchhundreds to thousands of unitsNo — and it causes haze if it survives

The profile we are aiming for​

Here is the target — the mix a conventional all-malt wort lands on, the profile beer yeast evolved alongside, and the reference point every mash design on this site is measured against:

SugarShare of wort carbohydrate (typical all-malt wort)
Maltose~50–60% — the backbone
Maltotriose~15–20%
Glucose~10–15%
Sucrose + fructose~2–5%
Dextrins (unfermentable)~20–25% — the body

Roughly three-quarters fermentable, maltose-led, with a dextrin remainder that gives the beer something to stand on. Barley brewers get this mix nearly free — a conventional barley mash lands on it every time. Gluten-free brewers do not. When external enzymes own conversion, the sugar mix is whatever the enzymes make it — which means the profile above is a design target, not a default, and every deviation from it (deliberate or accidental) shows up in the fermentation and the glass.1

What yeast does with the mix​

Yeast eats the table in order. Glucose first — greedily. Then maltose, then (for strains that can) maltotriose. Dextrins never.1

The order matters more than it sounds, because glucose is not just first — it suppresses the machinery for everything after it. A wort loaded with glucose tells the yeast "no need for maltose transport," and by the time the glucose runs out, the yeast has to switch metabolic gears mid-fermentation. That switch is where sluggish finishes, stalls, and off-character live. A maltose-forward wort ferments steadily from start to finish because the yeast runs one program the whole way.1

The endpoint matters too. Ferment everything and the beer is bone dry with nothing left for the palate. Leave dextrins and the beer keeps body and mouthfeel without sweetness — dextrins have almost no taste; what they have is presence.

The scissors: how each enzyme changes the mix​

Every conversion enzyme cuts the glucose chain differently, so every enzyme choice is a sugar-profile choice:

EnzymeWhere it cutsWhat it makesWhat that does to the beer
Alpha-amylase (bacterial, e.g. Termamyl)Middle of chains, randomlyShorter chains and dextrins — it liquefiesThins the mash; on its own leaves a barely-fermentable wort
Beta-amylaseTwo units at a time, from chain endsMaltoseBarley's native tool; weak in sorghum malt — the gap external enzymes fill
Fungal alpha-amylaseToward chain ends, maltose-leaningA maltose-forward profileThe closest external route to a "normal beer" wort
Glucoamylase (e.g. Amylase AG 300L)Single units off chain ends, and through branchesGlucose, relentlesslyVery fermentable, very dry — the light-beer tool. Uncontrolled, it strips the beer
Debranching enzymes (limit dextrinase, pullulanase)The branch pointsOpens branched dextrins for other enzymesMore complete conversion, drier finish

Two practical consequences fall straight out of this table.

First: alpha alone is not conversion. Bacterial alpha-amylase opens and thins the mash — essential work — but its product is mostly dextrins. Something else has to make the fermentable sugar: beta-amylase in barley brewing, an external saccharification enzyme in ours.

Second: the finishing enzyme sets the beer's character. Finish with glucoamylase and the wort runs glucose-heavy: fast start, dry finish, and the fermentation-order problem above. Finish with fungal alpha-amylase and the wort runs maltose-forward, like conventional beer. Neither is wrong. One is a choice for lightness and attenuation; the other is a choice for a conventional fermentation profile and more beer-like balance. Choosing without knowing is the only mistake.

Where our protocols sit on this map​

Mash Protocol 1 liquefies with bacterial alpha-amylase at the 190°F baseline, then finishes with Ondea Pro and a glucoamylase. That produces a fermentable, glucose-forward wort — a deliberate, proven trade: high attenuation and reliability, at the cost of the conventional maltose profile. It is also why the protocol is strict about deactivating the glucoamylase on schedule: that enzyme does not know when the beer is dry enough.

The maltose-forward alternative — protease rest, then a fungal-alpha finish — is the design space of Mash Protocol 3 (Proposed): a hypothetical next protocol nobody has validated at production scale, laid out as a research project for whoever gets there first.

How you see the sugar mix without a lab​

  • The iodine test detects long chains — starch and large dextrins. Iodine-negative means liquefaction finished; it says nothing about which fermentable sugars you made.
  • Final gravity against expectation is the poor man's sugar assay. Finishing far below target means over-conversion (glucoamylase ran long); far above target with healthy yeast means the wort was short on fermentables.
  • Fermentation shape tells on the profile: a violent start that dies early smells like glucose-heavy wort; a steady, even ferment suggests a balanced profile.
  • A real wort sugar profile (HPLC, from a brewing lab) is worth buying at least once per recipe — it turns all of the above from inference into data.

Practical takeaways​

  • Starch is chains; enzymes are scissors; the cut pattern is the beer.
  • Glucose ferments first and suppresses the rest — a glucose-heavy wort ferments hot then stumbles.
  • Maltose is the backbone of a conventional fermentation. Sorghum malt cannot make enough of it natively; the external enzyme system decides whether the wort gets it.
  • Dextrins are body. Total conversion is not the goal unless dry is the goal.
  • Know which profile your finishing enzyme builds, and deactivate it on schedule — it works for its optimum, not yours.

The Documented Evidence​

  • Yeast sugar uptake order and glucose repression — glucose is consumed first and represses maltose and maltotriose uptake; maltose is the major sugar of conventional brewer's wort: Stewart (2016).1
  • Maltotriose is the strain-dependent straggler — uptake of maltotriose is the slowest and least complete of the wort sugars, varying by yeast strain: Alves et al. (2008).2

References​

  1. Stewart, G.G. (2016). Saccharomyces species in the Production of Beer. Beverages 2(4):34. doi:10.3390/beverages2040034 ↩ ↩2 ↩3 ↩4

  2. Alves, S.L. et al. (2008). Molecular Analysis of Maltotriose Active Transport and Fermentation by Saccharomyces cerevisiae Reveals a Determinant Role for the AGT1 Permease. Applied and Environmental Microbiology 74(5):1494–1501. doi:10.1128/AEM.02570-07 ↩