Stuck fermentation defined
| How to tell if wine is "stuck"
| Causes of stuck fermentation | Prevention
and treatment of stuck fermentations |
Have you ever started a wine - and fermentation seems to start
normally enough - but all of a sudden, the signs of fermentation
(bubbles in your airlock, or falling Specific Gravity, for example)
seem to slow down or stop too soon? If so, you've experienced what's
known as a "stuck fermentation."
By definition, a stuck fermentation is a fermentation that has stopped
before all the available sugar in the wine has been converted to
alcohol and CO2. Were you to give up on the wine at this point,
it would taste semi-sweet and pretty bad. That would be a shame,
and what's more, a waste of good juice!
How did this situation occur? More importantly, what can you do
to restart fermentation and salvage your wine?
Is It Really Stuck?
Before we dive into these questions, we should first make sure
that our wine is stuck. Ask yourself these questions before you
start dumping yeasts, additives, and chemicals willy-nilly into
- What is the SG (specific gravity) of your wine? Do you
have proof that the SG is no longer falling, or is tremendously
sluggish? If you don't know (or aren't sure how to do this), we
recommend you see our article on
how to use the hydrometer. It explains the ins and outs of
measuring your wine's SG.
- Do you have a good airtight seal at your airlock? Is
your airlock firmly seated in the bung, and is the bung securely
seated in the mouth of the carboy? If not, this might explain
why you don't see bubbles in your airlock.
- Are you fermenting in hot weather or in a hot area? Yeast
works faster under higher (yet tolerable) temperatures, so your
wine may actually be finished fermenting before you realize it.
Luckily, stuck fermentations don't occur very often - but when
they do, it's important to make corrections right away and get the
fermentation going again.
Causes of Stuck Fermentations
More than likely, the cause of a stuck fermentation centers around
the wine yeast. Either something in the wine environment is preventing
the yeast from working properly, or there is a problem with the
Even if the proper yeast is used, most experienced vintners know
that wine yeast is pretty particular when it comes to fermenting
wine to dryness - the proper environmental conditions (such as cleanliness
and temperature) must be met, and nutrients (such as a balanced
source of DAP [diammonium phosphate], amino acids, minerals, and
vitamins) need to be available for the yeast to continue their hard
Wine yeast is most happy when:
- It's not too hot, and not too cold
- There's lots of food to eat
- No killer agents are present
- They live in sanitary conditions
- Oxygen is available (to kick off fermentation)
Sounds a lot like humans, huh? Using a little common sense, then
(which vintners seem to have a lot of!), we can easily extrapolate
the major causes of a stuck fermentation:
- Extreme fermentation temperatures - too high or too low.
- Using unsanitized equipment - dirty or unsanitary equipment
increases the possibility that microbiological factors such as
wild killer yeasts and bacteria will spoil your wine.
- Using old yeast - weakened or expired/out-of-date.
- Incorrect yeast used - match the proper yeast for your
wine (in the case of buying wine concentrate kits from grapestompers,
this is automatically done for you).
- Yeast not rehydrated before pitching - always rehydrate
yeast according to manufacturer's suggestions.
- Yeast rehydrated at too low or too high a temperature
- this can kill a large percentage of yeast cell population.
- Temperature shock when rehydrated yeast is introduced to
must - try to allow no more than a 5-7° C differential
between yeast mixture and must.
- Sulfite levels too high - adding too much metabisulfite;
failing to wait 24 hours after Campden applied to must before
pitching yeast; or high must pH, which can lead to high fermentation
- Pesticide residue on the exterior surface of grapes or fruits
- wash all grapes or fruits well before processing.
- Lack of nutrients, including a lack of nitrogen or certain
- Extremely high starting SG - too much sugar in must at
- Sugar has all been utilized - you don't want your starting
SG to be too low either!
- Too much CO2 in your wine - don't forget to degas.
- Naturally occurring sorbate in must - as in the case
Prevention of Stuck Fermentations
Here are some things the home winemaker can do to prevent
- Monitor and ensure proper fermentation temperatures.
- Ensure proper sanitation - learn
how to sanitize equipment
- Use fresh yeast.
- Use the proper yeast for the wine you're making - don't
guess or use a packet of yeast just because it's handy.
- Properly rehydrate yeast before pitching.
- Pitch the yeast within 20 minutes of rehydrating it.
- Maintain proper free SO2 levels - the amount of metabisulfite
to add to your wine depends on pH of wine.
- Add yeast nutrient before pitching yeast - Item # 2733.
- Keep your starting SG to reasonable levels (1.090 - 1.100
or lower). If you don't currently have a hydrometer, buy one (they're
inexpensive - about $5) and learn
how to use it.
- Aerate the must properly by vigorous stirring, just before
pitching the yeast. This will introduce the oxygen needed to "kick
Treatment of Stuck Fermentations
And here's what to do if you get stuck... and remember - always
start with the simplest things first. Resist the urge to add yeast
or additives until you've tried the easy things.
- Adjust the temperature of your wine. In most cases we've
seen, simply warming your wine to 70-75° F for a couple of
days will get the ball rolling.
- Rouse the yeast by swishing or stirring the lees (trub)
- sometimes moving the yeast around in the wine will get fermentation
- WARNING: Although it may be tempting, don't add vitamins (yeast
nutrient) during stuck fermentations. Leftover vitamins can stimulate
spoilage microbes. Only add a yeast nutrient before or
as you pitch your yeast. If you want to add a yeast
energizer at this point (which is not the same thing as yeast
nutrient), that's OK. Simply go to the local drug store and ask
the pharmacist for some Thiamin HCL (thiamin hydrochloride). Add
25 mg. per gallon of wine and mix well.
- Remove the old yeast by racking the wine, then re-inoculate
with fresh yeast, preferably a killer strain like Lalvin
EC-1118 or Red Star Premier Cuvee. In a pinch, you could even
use a Red Star Champagne yeast. We want to get rid of the old
yeast because yeast cells seem able to detect the presence of
other dying cells, and are more likely to get "lazy"
- If you detect there is a nitrogen deficiency (less than 200
mg/L fermentable nitrogen), addition of DAP (diammonium
phosphate dibasic - commonly known in the winemaking industry
as Fermaid*) is called for.
If none of the above seem to help restart your fermentation within
a couple or three days, it's time to bring in the heavy hitters:
- Make a yeast starter by pulling off approximately 1/2 gallon
of must, and add 1.5 to 2 teaspoons of yeast energizer (thiamin
HCL) and 1 packet of "killer" or champagne yeast. Mix
well, cover loosely and place in a warm spot. Once you have a
vigorous fermentation you can add it back to the original must.
- Make a different kind of starter: use about a 1/2 cup of warm
water, dissolve 1 teaspoon of sugar in the water, add some orange
juice to this mix, make sure the temperature is about 90°
F, before adding a packet of Red Star Premier Cuvee or Lalvin
EC-1118 yeast to this mixture. Wait until it really gets working.
Take about a gallon of your must and warm it up to about 68°
to 70° F. Now add the yeast starter to the gallon of must,
as it starts to work and gets going, SLOWLY add small portions
of the stuck fermentation to that which is working. You should
not add more than a quart, make sure the temperature of that which
you are adding is at least 70° F. As the volume of the working
must gets larger, you can add larger portions to the fermentation.
Make sure the temperature is at least 70° F before you add
Using one of these methods should help get your fermentation restarted.
Clicking on any of the reference links below will open a new browser
Fermaid contains diamonium phosphate (DAP), magnesium sulfate, yeast
hulls and vitamins.
DAP addition of 1 g/L (8.3 lb/1,000 gal) provides about 258 mg/L
fermentable N. This is greater than the supplier's recommended level.
In the US the legal limit of DAP is 960 mg/L which is equal to 208
mg N/L. Fermaid K at 2 lb/1000 gal (25 g/hL) = 25 mg N/L while DAP
at 2 lb/1000 gal (25 g/hL) = 50 mg N/L. As indicated, fermentable
nitrogen concentration in juice or wine can be easily estimated
(Zoecklein et al., 1995).
Many musts lack sufficient nitrogen, vitamins and other ingredients
needed by yeasts during their growth phase for healthy fermentations.
Levels of greater than 200 mg/L fermentable nitrogen are required
for healthy fermentations. Supplementation should be made using a
balanced source of DAP (diammonium phosphate), amino acids, minerals,