Stuck Fermentation: How to Diagnose and Restart It

A wine fermentation is stuck when the hydrometer reading stops falling while there is still sugar left, typically somewhere above 1.000 for a wine meant to finish dry. Before you treat it, confirm it with two readings a few days apart, because a quiet airlock on its own proves nothing. Then work through the fixes from simplest to hardest: warm the wine to around 68 to 70°F, rouse the yeast, add yeast nutrient, and if nothing changes in about two days, restart it with a strong, alcohol-tolerant yeast such as Lalvin EC-1118, added step by step.

The sequence here follows Bob Peak’s WineMaker Magazine guide Restart Stuck Fermentations, whose full restart is adapted from a Scott Laboratories protocol, scaled down for home batches.

Is Your Fermentation Really Stuck?

Most “stuck” fermentations that home winemakers ask about are not stuck at all.

WineMaker’s test for a juice or carboy fermentation is the same: if bubbles stop and the hydrometer shows sugar remaining, you are stuck. Take readings two or three days apart; our guide on how to use a hydrometer covers the method and temperature correction. Typical timings are in how long wine takes to ferment.

What Causes a Stuck Fermentation

Temperature

Every yeast has a working range. WineMaker notes that some strains manage around 50°F while others need about 68°F to thrive, and that very warm fermentations can slow, stop or kill the yeast. Wine kit makers such as Winexpert ask you to keep the fermentation area between 68 and 77°F for the whole process. The Lalvin EC-1118 product sheet gives that strain a range of 50 to 86°F (10 to 30°C).

Nutrients

According to WineMaker, the most common nutrient problem is a shortage of nitrogen the yeast can use, and a stressed, hungry yeast often gives itself away with a rotten egg smell of hydrogen sulfide. Fruit wines are more prone to this than grape wines, which is why most fruit wine recipes add yeast nutrient at the start.

Sugar and alcohol

The most common reason for a stall late in fermentation is alcohol. If the must started with more sugar than the yeast can turn into alcohol, it stops with sugar left. WineMaker suggests checking any must above about 24°Brix (a gravity of roughly 1.100) against the yeast’s alcohol tolerance before you pitch, and diluting with water if needed. Our guide on how to make wine stronger covers yeast alcohol limits, and the sugar calculator helps you avoid overshooting.

How to Fix a Stuck Fermentation: Start Simple

1. Warm it up, slowly

Move the fermenter to a room at about 68 to 70°F, or wrap it, and let it warm over a day. WineMaker warns against warming or cooling quickly, which can further damage the yeast that is still alive. If it starts again, leave it alone.

2. Rouse the yeast

For a sluggish carboy fermentation, WineMaker suggests removing the airlock and swirling the carboy or stirring with a sanitized spoon to get the yeast back into suspension. Early in fermentation, a little air helps, because yeast needs oxygen to grow.

3. Add yeast nutrient

WineMaker gives diammonium phosphate (DAP) at about 1 gram per gallon, or a complete nutrient such as Fermaid K or Fermaid O at 1 to 2 grams per gallon. Fermentation should pick up within a day if nitrogen was the problem. Use less late in fermentation, when there is little sugar left for the yeast to use it on.

4. Re-pitch if it was a cold or sulfite problem

If warming did not wake it, WineMaker says it is usually safe to add a fresh pack of the same yeast. If there is still no activity after about two days, move to the full restart.

How to Restart a Stuck Fermentation (Full Restart)

When alcohol, wild yeast or toxins from the first fermentation are to blame, dropping a fresh packet into the wine rarely works, because new yeast cannot cope with alcohol it has not adapted to. The full restart builds a small, vigorous starter and feeds it the stuck wine in stages. These are WineMaker’s rates, with our arithmetic for 1 and 5 gallon batches.

1. Check that the yeast mixture and the restart container are within 18°F (10°C) of each other; if not, add a little of the restart mixture to the yeast and stir.
2. Stir the yeast into the restart container and wait 20 to 30 minutes.
3. Add stuck wine equal to 10% of the batch to the container. Wait 20 to 30 minutes.
4. Add 20% of the batch. Wait 20 to 30 minutes. Repeat three more times.
5. Add the rest of the stuck wine, fit the airlock, and keep it warm.

EC-1118 is the yeast WineMaker names alongside Uvaferm 43 for this job; Lallemand lists its alcohol tolerance at 18%. Our wine yeast guide compares it with other strains.

Restart supply	Lalvin EC-1118 Wine Yeast, 10 pack Editor's ChoiceTop pick	Fermax Yeast Nutrient, 1 lb	Fermaid O Yeast Nutrient, 2 oz	North Mountain Supply Go-Ferm, 3 oz
Product
Job in a restart	Restart yeast	Nutrient for the stuck wine	Complete organic nutrient	Rehydration nutrient for the restart yeast
Maker's rate	5 g sachets	1 tsp per gallon before fermentation	20 g/hL twice during fermentation	See jar
Key fact	Alcohol tolerance 18% (Lallemand)	Improves speed and completeness of fermentation (maker)	Yeast-derived organic nitrogen, no DAP (maker)	Helps a faster start and fewer sulfur smells (maker)
Price tier	$	$	$	$
Buy	Check price	Check price	Check price	Check price

Editor's Choice

Lalvin EC-1118 Wine Yeast, 10 pack

Job in a restart

Restart yeast

Maker's rate

5 g sachets

Key fact

Alcohol tolerance 18% (Lallemand)

Price tier

$

Check price

Fermax Yeast Nutrient, 1 lb

Job in a restart

Nutrient for the stuck wine

Maker's rate

1 tsp per gallon before fermentation

Key fact

Improves speed and completeness of fermentation (maker)

Price tier

$

Check price

Fermaid O Yeast Nutrient, 2 oz

Job in a restart

Complete organic nutrient

Maker's rate

20 g/hL twice during fermentation

Key fact

Yeast-derived organic nitrogen, no DAP (maker)

Price tier

$

Check price

North Mountain Supply Go-Ferm, 3 oz

Job in a restart

Rehydration nutrient for the restart yeast

Maker's rate

See jar

Key fact

Helps a faster start and fewer sulfur smells (maker)

Price tier

$

Check price

How to Prevent a Stuck Fermentation

• Measure the starting gravity and match it to your yeast’s alcohol tolerance.
• Keep the temperature steady in the yeast’s range; avoid cold garages and sunny windows.
• Add yeast nutrient to fruit and honey musts, which are often short of it.
• Wait 24 hours after sulfiting fresh fruit before adding the yeast; see our Campden tablet guide.
• Pitch a healthy dose of cultured wine yeast, rehydrated as the packet says, rather than relying on wild yeast.