Stuck Fermentation or Infected Wine? Fortification Turns a Setback Into Art
Posted by Matteo Lahm on 12th Feb 2026
You open your fermenter and something feels wrong. The airlock has gone quiet too soon. Your gravity has stalled at 1.028 and refuses to move. Or worse, a thin pellicle has formed across the surface. In that moment, it is easy to assume the batch is finished in the worst way possible.
The most common advice you will hear is blunt. Dump it and start over.
But you can and should pause before you do. This is not a setback. It's an opportunity, if you have the knowledge and wherewithal to take it.
Before modern yeast strains, temperature control, and sanitation protocols, instability was a constant companion to winemaking. Fermentations stalled. Barrels turned. Oxygen crept in. If a batch failed, there was no quick trip to the supply store and no replacement kit arriving in two days. A lost vintage often meant no wine for the year.
Out of that reality came adaptation. In Portugal, Spain, and other maritime regions, producers learned that adding distilled grape spirit could preserve a wine that might otherwise spoil during storage or long sea voyages. What began as a practical measure became tradition. Wines like Port and Sherry were not created as novelties. They were solutions. Alcohol was used deliberately to stop fermentation, stabilize residual sugar, and protect wine from microbial and oxidative damage.
Fortification was not indulgence. It was insurance. It allowed winemakers to salvage value from uncertain fermentations and protect their work against unpredictable conditions. Over time, the technique evolved into celebrated styles, but its origin was grounded in necessity and control.
When you raise a wine’s alcohol into the seventeen to twenty percent range, yeast can no longer function and most spoilage organisms are inhibited. Alcohol becomes your stabilizer. Instead of fighting a stuck fermentation or worrying about renewed microbial growth, you can halt the process decisively and permanently.
If your fermentation has stopped with residual sugar remaining, you are not simply holding a failed dry wine. You are holding the base of a sweet fortified wine. Rather than attempting a risky restart that introduces oxygen and stress, you can pivot intentionally. By adding neutral grape spirit in a calculated amount, you lock in the current sugar level and prevent further fermentation. What looked like a flaw becomes part of the style.
If you are dealing with early pellicle formation, timing is critical. If volatile acidity is still low and the wine does not smell sharply vinegary, fortification can stop further microbial activity. It will not repair advanced spoilage, but it can prevent a manageable issue from escalating. The key is honest sensory evaluation before you act.
The shift you must make is mental. Not every compromised batch belongs in the drain. Sometimes it needs a deliberate intervention.
When You Should Consider Fortifying
You may be a good candidate for fortification if:
• Your fermentation is stuck with measurable residual sugar
• The wine tastes clean aside from sweetness
• A pellicle has formed but volatile acidity remains low
• There is no visible mold growth
• The wine does not smell strongly acetic
You should not fortify if:
• The wine smells sharply of vinegar
• Volatile acidity dominates the palate
• Oxidation is severe
• Mold is present
Expanded Technical Guidelines
Before you add any spirit, slow down and evaluate.
Assessment:
• Record current volume
• Confirm current specific gravity
• Estimate existing alcohol from original gravity
• Taste carefully for volatile acidity and structural soundness
Spirit selection:
• Use neutral grape brandy or grape spirit
• Verify the alcohol percentage, typically around forty percent
• Avoid flavored or heavily aromatic liquors
Target range:
• Aim for at least seventeen percent total alcohol
• Eighteen to twenty percent offers greater stability
Blending practice:
• Perform the alcohol calculation before pouring
• Add spirit gradually while stirring thoroughly
• Allow time for integration before judging balance
• Consider oak for structure and complexity
Estimating How Much Spirit to Add
Use this formula to estimate the volume of spirit required:
Vs = Vw × (At − Aw) ÷ (As − At)
Where:
Vw = current wine volume
Aw = current wine alcohol percentage
As = spirit alcohol percentage
At = target alcohol percentage
Vs = volume of spirit to add
Example:
You have 19 liters of wine at 12 percent alcohol.
You want to reach 18 percent using 40 percent brandy.
Vs = 19 × (18 − 12) ÷ (40 − 18)
Vs = 19 × 6 ÷ 22
Vs ≈ 5.2 liters of brandy
Measure carefully and confirm your numbers before committing.
Before you reach for the drain, remember this. Dumping the batch feels decisive, but it teaches you nothing. It is an emotional reaction disguised as control. You remove the problem, but you also remove the opportunity to understand it. You never sharpen your judgment. You never test your calculations. You never learn how alcohol, sugar, and stability interact in real time.
Fortifying forces you to slow down. You measure gravity. You estimate alcohol. You assess volatile acidity honestly. You run the numbers. You choose a target. You intervene deliberately. That process builds competence. It turns panic into precision and uncertainty into structure. When you choose intervention over abandonment, you stop reacting like a hobbyist and start thinking like a winemaker.
And there is a practical reward as well. Instead of pouring your work down the drain, you end up with a rich after dinner wine that can age for years. Fortified wines are naturally stable and often improve with time, developing deeper integration and complexity. What began as a problem batch can become a bottle you open on holidays, pour alongside dessert, or share slowly by the glass. You will have something you can drink in ten years, or longer. Imagine drinking it on special occasions and every year, it's different. That is when practicality becomes artitic expression.
It also makes a memorable gift. A handcrafted fortified wine carries a story. It is not just something you made. It is something you rescued, calculated, and shaped intentionally. That narrative adds weight to the bottle. So before you dump it, consider this. You are not deciding whether the batch lives or dies. You are deciding whether you want to discard a lesson or turn it into something you will proudly pour for years to come.