fermentation
Hop creep
Explain the renewed fermentation that dry hopping can start in beer that had already finished, and the over-carbonation and dryness that follow it.
Also called dry hop creep, secondary refermentation.
What is actually happening
- Fermentation finishes. Gravity flattens and holds. The dextrins left behind are long-chain sugars the yeast cannot ferment, and they are what the beer’s body is made of.
- Dry hops go in. Hops carry amylase and other diastatic enzymes. In finished beer they start breaking those dextrins into sugars the yeast can ferment after all.
- It starts again. Any yeast still in suspension ferments the newly available sugar. The beer attenuates further, gains alcohol, loses body, and produces gas — which in a sealed package is a hazard rather than a quality complaint. Diacetyl frequently returns with it.
Hops carry small amounts of amylase and other diastatic enzymes. Added to finished beer, they break down dextrins the yeast could not ferment — long-chain sugars that were supposed to stay behind as body — into sugars it can.
Any yeast still in suspension then ferments them. The beer that was stable at its final gravity attenuates further, gains alcohol, loses body and produces carbon dioxide it was not expected to produce.
In a package that is a real hazard rather than a quality complaint: the extra gas has nowhere to go, and the result is gushing or, in the worst case, a failed container. It also regenerates diacetyl, which is why a heavily dry-hopped beer can taste of butterscotch weeks after a clean diacetyl rest.
The usual controls are a warm rest after dry hopping to let the refermentation finish before packaging, or removing the yeast first so there is nothing left to ferment the newly available sugar.
What goes wrong here
Risks rather than certainties. This step does not cause these faults; getting it wrong can.
- Overcarbonation — Too much dissolved CO₂, from over-priming, incomplete fermentation before packaging, or contamination.
- Gushing — Beer that erupts on opening, caused either by refermentation in the package or by fungal proteins from mould-affected barley.
- Diacetyl — A buttery compound with a very low threshold — normally a sign of rushed fermentation, but traditional at trace levels in some Czech lagers.
Styles where this step is decisive
- New England IPA
Hazy, soft and intensely aromatic: tropical and stone fruit hop character with deliberately low bitterness and a full, juicy body.
- Double IPA
IPA scaled up: more strength, more hops and more bitterness, while staying dry enough to remain drinkable.
- American IPA
The defining modern craft beer: intense citrus, tropical and resinous hop aroma over a lean malt base, finishing firmly bitter.
Related steps and concepts
- Dry hopping — The step that causes it.
- Biotransformation — The same enzyme activity, wanted rather than not.
- Diacetyl rest — What it can undo.
Also at the fermentation stage
Biotransformation · Bottom fermentation · Diacetyl rest · High-gravity brewing · Mixed fermentation · Open fermentation · Pitching · Pressure fermentation · Primary fermentation · Spontaneous fermentation · Top fermentation · Yeast harvesting
See the whole process in order on how beer is made.
Last reviewed 2026-08-16.