Fault
Unintended sweetness
Beer that finishes sweeter than intended, from under-attenuation, excess crystal malt, or a mash run too warm.
Also called cloying, underattenuated, syrupy.
What it tastes and smells like
Styles this tends to affect
Not where it belongs — where it is most likely to appear when something has gone wrong.
- Alcohol-free stout — An alcohol-free dark beer where roasted grain does most of the work — one of the more successful conversions in the category.
- London brown ale — A low-strength, notably sweet dark brown ale from London, now largely extinct as a commercial style.
- Milkshake IPA — A hazy IPA with lactose and fruit added for sweetness and a fuller, creamier body.
- Pastry stout — A heavily adjuncted sweet stout built to taste like dessert, using lactose, vanilla, cocoa and similar additions.
- Sweet stout — A stout sweetened with lactose, giving chocolate and cream character over a full body and gentle roast.
- Tropical stout — A strong, sweet, fruity stout brewed for tropical markets, with less roast bite than its Irish relatives.
If you are drinking it
A beer that tastes syrupy and never quite finishes is usually a recipe or process issue rather than spoilage. Harmless.
Not a safety issue. Beer’s alcohol, hop compounds and low pH make it inhospitable to organisms that cause illness.
What causes it
| Cause | Stage | How often | Who can act |
|---|---|---|---|
| A mash held hot leaves more unfermentable dextrin behind, so the beer finishes sweeter whatever the yeast does. Above about 72 °C no further fermentable sugar is produced at all. The temperature at which beta-amylase actually stops is contested in the literature, so the useful rule is the direction rather than a number: cooler for a dry beer, warmer for a full one | mashing | most common | brewer |
| Too much crystal or caramel malt. Its sugars are largely unfermentable, so it sets residual sweetness directly. | raw materials | most common | brewer |
| Yeast dropping out or stalling before terminal gravity, leaving fermentable sugar behind. | fermentation | common | brewer |
If you are brewing it
- Brewer: Mash at 64–66 °C for a more fermentable wort, and verify mash temperature with a calibrated thermometer. (prevents)
- Brewer: Keep crystal malt below about 10% of the grist for most styles. (prevents)
- Brewer: Pitch adequate healthy yeast, keep fermentation temperature in range, and rouse gently if it stalls early. (mitigates)
Where in the process this comes from
Steps that can produce this fault when they go wrong. Each links to what the step is for and how it is controlled.
- Arrested fermentation — Stop fermentation deliberately and early — by chilling, filtering or pasteurising — so little alcohol is produced.
- Mashing — Hold milled malt in hot water so the grain’s own enzymes convert its starch into sugars that yeast can ferment.
Often confused with
- Stalled fermentation — high final gravity, sweet and underdeveloped
- Diacetyl — butter, butterscotch
Evidence
What BeerHQ knows about this, and how. Every statement carries the state of the evidence behind it rather than being presented flatly as fact.
The temperature at which beta-amylase stops working is genuinely unsettled, and the round numbers repeated in brewing guidance sit between two incompatible sets of published figures.
— The long-standing figures, tabulated in the review, put beta-amylase’s temperature optimum at 55–65 °C and its inactivation at 74 °C.
— Recent work the review cites puts the optimum far lower, between 45 °C and 50 °C, with inactivation beginning at 52.5 °C and only 10% of activity remaining after 3.4 minutes at 60 °C.
The review sets both out without resolving them. The practical guidance a brewer acts on — mash cool for a dry beer, warm for a full one — is unaffected either way, which is why the disagreement has survived; but a specific inactivation temperature is not something BeerHQ can state.
Genuinely contested Credible sources disagree, so both positions are given rather than one.
Source: Laus et al., "Review on Recent Advances and Novel Approaches in Milling and Mashing" (2025), section 3.1.3, amylolytic activity during mashing (Compr Rev Food Sci Food Saf 24(5):e70239)
Above about 72 °C no further fermentable sugar is produced in the mash: alpha-amylase continues to break starch down but only into dextrins, which yeast cannot ferment and which remain in the finished beer as body and sweetness.
Checked against the source
Source: Laus et al., "Review on Recent Advances and Novel Approaches in Milling and Mashing" (2025), sections 3.1.2 and 3.1.3 (Compr Rev Food Sci Food Saf 24(5):e70239)