Wine Not Fermenting: Troubleshooting a Dead Must

Why Won't Your Must Start Fermenting?

You prepared your must, added yeast, and waited expectantly — but nothing is happening. No airlock bubbling, no foam, no yeasty smell, no drop in specific gravity. A must that refuses to start fermenting is frustrating, but it is also one of the most diagnosable and fixable problems in home winemaking.

Unlike a stuck fermentation (where fermentation started and then stopped), a must that never begins fermenting has a different set of potential causes, most of which are correctable once identified. The key is systematic troubleshooting rather than guessing.

First, Confirm It Is Truly Not Fermenting

Before troubleshooting, verify that fermentation has genuinely not started. Some signs of early fermentation are subtle:

• Tiny bubbles forming on the surface or sides of the vessel
• A slight yeasty or bready smell when you open the fermenter
• A very slow but measurable drop in specific gravity over 24-48 hours
• A slight cloudiness developing in previously clear juice

Take a hydrometer reading and compare it to your original gravity. If the reading has dropped even slightly, fermentation has begun — it may just be proceeding slowly. If the reading is identical to your starting gravity after 48 hours, the must is truly not fermenting.

Also check for seal leaks. If your fermenter lid or bung is not sealed tightly, CO2 may be escaping without passing through the airlock. The lack of airlock bubbling does not always mean the lack of fermentation.

Step-by-Step Troubleshooting

Step 1: Check the Temperature

Measure the must temperature with a sanitized thermometer. Yeast will not become active below approximately 50°F (10°C), and most strains need 60-75°F (15-24°C) to start fermenting within a reasonable timeframe.

If the must is cold, move the fermenter to a warmer location or use a fermentation heating wrap. Allow 12-24 hours at the correct temperature before concluding the yeast is dead.

Step 2: Evaluate the Yeast

Consider the condition of the yeast you used:

• Expiration date: Was the yeast past its use-by date? Old yeast has dramatically lower viability.
• Storage history: Was the yeast stored in a hot location? Heat kills yeast cells over time. Dry yeast should be stored in the refrigerator.
• Rehydration: Did you rehydrate the yeast properly in 104°F (40°C) water? Or did you sprinkle it directly on cold must? While many yeasts can tolerate direct pitching, cold or high-gravity musts are harder to start without proper rehydration.
• Quantity: Did you pitch enough yeast? One 5-gram packet per 5-6 gallons is standard. Under-pitching slows or prevents startup.

Step 3: Check for Preservatives

This is one of the most common reasons a must will not ferment. Many commercial fruit juices, concentrates, and even fresh-looking fruit products contain preservatives that prevent yeast from growing:

• Potassium sorbate: Prevents yeast reproduction. Common in juice concentrates, wine kits that include finishing additives, and preserved fruit.
• Sodium benzoate: Inhibits yeast growth. Found in many commercial juices.
• Sulfite (SO2): If you added potassium metabisulfite before pitching yeast, excessive levels (above 75 ppm) can inhibit or kill yeast. Standard practice is to add sulfite 24 hours before pitching yeast, allowing SO2 levels to drop.

Read ingredient labels carefully. If your juice contains sorbate or benzoate, starting fermentation will be extremely difficult or impossible without diluting the must with preservative-free juice.

Step 4: Measure pH and Gravity

Test the must's pH and specific gravity. A pH below 2.8 is hostile to most yeast strains. A specific gravity above 1.130 creates osmotic stress that makes startup difficult.

If pH is too low, add potassium bicarbonate at 1 gram per gallon and retest. If gravity is very high, consider diluting with water to bring it below 1.110 before repitching yeast.

Step 5: Check for Sanitizer Residue

If you used a sanitizer that requires rinsing (such as bleach) and did not rinse thoroughly, residual chemicals may be inhibiting yeast. Even no-rinse sanitizers like Star San can be problematic if used in excessively high concentrations or if large puddles remain in the vessel. While properly diluted Star San is yeast-safe, an inch of undiluted sanitizer at the bottom of your fermenter could impair the yeast pitch.

Step 6: Repitch with Fresh Yeast

If you have identified and corrected the likely cause (temperature, preservatives, pH, etc.), prepare a fresh yeast starter and repitch:

1. Rehydrate a new packet of robust yeast (Lalvin EC-1118 is the most reliable for difficult startups) in 104°F (40°C) water with GoFerm rehydration nutrient at 1.25 grams per gram of yeast.
2. Wait 15-20 minutes until the yeast is foamy and active.
3. Add a small amount of the must (1/4 cup) to the yeast suspension to acclimate it.
4. Wait 15-20 minutes for renewed activity.
5. Add another 1/4 cup of must.
6. Once the starter is actively bubbling, pitch it into the full must.
7. Stir the must vigorously to incorporate oxygen, which yeast needs for initial cell membrane synthesis.

Step 7: Add Nutrients

If you have not already, add yeast nutrient to the must. Use Fermaid-K at 1/2 teaspoon per gallon or GoFerm Protect Evolution during rehydration. Adequate nutrition supports the initial yeast population expansion that must occur before vigorous fermentation begins.

Step 8: Wait and Monitor

After repitching, allow 24-48 hours before expecting visible signs of fermentation. Early fermentation activity may be subtle — look for fine bubbles, a slight change in surface appearance, or a barely perceptible gravity drop. If there is still zero activity after 48 hours with corrected conditions and fresh yeast, revisit the troubleshooting steps and consider whether preservatives are the issue.

Special Situations

Preservative-Laden Juice

If your must contains potassium sorbate, fermentation will be very difficult to initiate. Sorbate does not kill yeast but prevents reproduction, so a massive yeast pitch may begin fermenting but the population cannot sustain itself. Options include:

• Dilute the must with at least 50% preservative-free juice or water plus sugar
• Overpitch with 2-3 packets of a highly vigorous strain and accept that fermentation may be sluggish
• Accept the limitation and use the juice for a non-fermented beverage instead

Very High Gravity Musts

Musts with starting gravity above 1.120 (potential alcohol above 16%) create osmotic pressure that can prevent yeast startup. For these musts, consider step-feeding — begin fermentation at a moderate gravity (1.090-1.100) and add sugar in increments as the gravity drops. This is common practice in mead-making and high-alcohol wine production.

Cold Must from Refrigerated Juice

If your juice came straight from the refrigerator at 35-40°F (2-4°C), allow it to warm to at least 65°F (18°C) before pitching yeast. Cold-shocking yeast by pitching it into frigid must can kill a significant percentage of cells before they ever activate.

Frequently Asked Questions

How long should I wait before deciding my must won't ferment?

Allow at least 48 hours after pitching yeast before concluding that fermentation has not started. Some yeast strains, particularly in cool conditions or high-gravity musts, have a lag phase of 24-48 hours before visible activity begins. If nothing has changed after 48 hours at proper temperature, troubleshoot.

Can I add more yeast on top of the first pitch?

Yes, but first identify why the original pitch failed. Simply adding more of the same yeast without fixing the underlying problem will likely fail again. Correct the conditions first, then repitch with a fresh, properly rehydrated yeast.

Does the type of water I used matter?

Yes. Highly chlorinated tap water can inhibit yeast. If you used unfiltered tap water to dilute your must, residual chlorine or chloramine may be the issue. Use spring water, filtered water, or tap water treated with a Campden tablet (1/4 tablet per 5 gallons neutralizes chlorine) for your must.

Will my must spoil while I troubleshoot?

If the must was sulfited at crush (50 ppm SO2), it has some protection against spoilage bacteria. If no sulfite was added, the must is vulnerable. Work quickly to get fermentation started — a fermenting must is protected by yeast activity, CO2 production, and alcohol. An unfermented must is an open invitation for spoilage organisms.

Can I use bread yeast if wine yeast won't work?

Bread yeast (Saccharomyces cerevisiae) will technically ferment sugar to alcohol, but it produces unpleasant off-flavors, has low alcohol tolerance, and does not flocculate well. It should be a last resort only. If wine yeast is not working, the problem is almost certainly environmental (temperature, preservatives, pH) rather than the yeast type, and bread yeast will face the same obstacles.