The most reliable way to tell when wine is done fermenting is to take hydrometer readings on consecutive days. When the specific gravity holds steady at or below 0.998 for two to three days in a row, primary fermentation is complete. But a hydrometer isn’t the only tool at your disposal, and understanding several indicators together gives you the clearest picture.
What a Hydrometer Tells You
A hydrometer measures the density of your wine relative to water. Before fermentation, dissolved sugar makes the liquid denser than water, giving you an original gravity somewhere around 1.080 to 1.100 for most wines. As yeast converts that sugar into alcohol, the density drops. Alcohol is lighter than water, so a fully fermented dry wine typically lands between 0.990 and 0.998.
A single low reading isn’t enough. Fermentation can pause temporarily and restart, so you need to confirm the gravity is stable. Take a reading, wait 24 hours, and take another. If the number hasn’t budged over two or three consecutive days, the yeast has finished its work. This is the gold standard because it removes guesswork entirely.
Why Refractometers Need Correction
Refractometers are popular for checking sugar levels in grape juice before fermentation because they only need a few drops of liquid. Once alcohol enters the picture, though, the readings become unreliable. Alcohol bends light differently than sugar does, so a refractometer will show a misleadingly high Brix number in a fermenting or finished wine. Online correction calculators exist that use both the original Brix reading and the current refractometer reading to estimate true sugar content, but these involve multiple approximations. Don’t expect a corrected reading to land on exactly zero Brix when fermentation is done. For a definitive answer, stick with a hydrometer.
Visual and Airlock Cues
If you don’t have a hydrometer, your eyes and your airlock can still tell you a lot. During active fermentation, you’ll see vigorous bubbling in the airlock, often several times per minute, along with a foamy cap (called “krausen” in brewing) on the surface of the wine. As fermentation winds down, bubbling slows dramatically.
A good rule of thumb: if 14 days have passed since you pitched your yeast and the airlock shows no activity for at least a minute or two of watching, fermentation has likely finished. Be patient, though. Temperature swings, changes in barometric pressure, and even a poorly sealed lid can cause airlock bubbles that have nothing to do with active fermentation. Likewise, a slow leak in your fermenter can let CO2 escape without ever passing through the airlock, making a still-active ferment look finished. That’s why airlock activity is a useful clue but not definitive proof.
Clarity is another visual signal. As yeast cells run out of sugar and die off, they settle to the bottom of the fermenter as a layer of sediment called lees. The wine above gradually shifts from cloudy to translucent. A thick, compact layer of lees with increasingly clear wine above it is a strong visual indicator that fermentation has wrapped up.
Tasting for Dryness
Your palate can supplement your other observations. A finished dry wine should not taste noticeably sweet. Sugar concentrations above roughly 0.2% (about 2 grams per liter) are generally needed before most people perceive sweetness on the tongue. Under most wine law standards, a wine is classified as “dry” at 4 grams per liter of residual sugar or less.
When you taste a sample, pay attention to two things. First, is there residual sweetness? A hint of fruity flavor isn’t the same as sweetness from unfermented sugar. Second, do you feel a prickling or fizzy sensation on your tongue? That’s dissolved carbon dioxide, a byproduct of active fermentation. If both sweetness and fizz are absent, that lines up with a finished ferment. Tasting alone isn’t precise enough to catch small amounts of residual sugar, but combined with stable hydrometer readings and a quiet airlock, it rounds out the picture nicely.
Typical Timelines for Primary Fermentation
Temperature is the biggest factor controlling how fast fermentation proceeds. Warmer conditions (20 to 30°C, or roughly 68 to 86°F) speed things up, while cooler temperatures (10 to 15°C, or 50 to 59°F) slow the process considerably. As a general guide, red wines typically finish primary fermentation in 5 to 10 days because they’re often fermented at warmer temperatures to extract color and tannin. White wines, usually kept cooler to preserve delicate aromas, can take 10 to 21 days.
These are averages, not guarantees. A high-sugar must, a particularly cool cellar, or a less vigorous yeast strain can push timelines well beyond these ranges. Let your measurements, not the calendar, determine when you move to the next step.
Stuck Fermentation vs. Finished Fermentation
One of the trickiest situations in winemaking is distinguishing a wine that’s truly finished from one that has stalled partway through. A stuck fermentation stops before all the fermentable sugar has been consumed, leaving you with a wine that’s sweeter and lower in alcohol than intended.
The best defense is monitoring from the start. The Australian Wine Research Institute recommends checking Brix (or specific gravity) and temperature twice daily and plotting those numbers as a fermentation curve. A healthy ferment shows a steady, predictable decline in sugar. If the curve flattens out while the gravity is still well above 1.000, something has gone wrong. Common culprits include temperatures that have drifted too cold or too warm for the yeast, nutrient deficiency, or alcohol levels that have reached the yeast’s tolerance limit.
If you only start checking near the end, here’s a practical test: your hydrometer reads, say, 1.010 and hasn’t moved in three days. That’s not a finished wine. A dry wine should be below 0.998. A reading stuck above 1.000 with no movement signals a stall that needs intervention, such as gently warming the fermenter, adding yeast nutrients, or pitching a fresh, alcohol-tolerant yeast strain.
Malolactic Fermentation Is a Separate Step
Primary fermentation (yeast converting sugar to alcohol) is what most people mean when they ask if their wine is “done.” But many red wines and some whites go through a second biological process called malolactic fermentation, where bacteria convert sharp malic acid into softer lactic acid. This can happen spontaneously or be initiated by adding a bacterial culture after primary fermentation finishes.
Malolactic fermentation doesn’t produce obvious bubbling the way primary fermentation does, so it’s harder to track visually. The standard method is paper chromatography: you spot a small wine sample onto chromatography paper, develop it in a solvent, and look for the presence or absence of malic acid. When the malic acid spot disappears and only lactic acid remains, the conversion is complete. Inexpensive paper chromatography kits are available at most homebrew suppliers. If you skip this step and bottle while malolactic fermentation is still active, the wine can develop unwanted fizziness or off flavors in the bottle.
Degassing Before Bottling
Even after fermentation has genuinely finished, your wine will still contain dissolved CO2. This is normal, but it needs to be addressed before bottling. Excess dissolved gas makes wine taste sharper and more acidic than it actually is, and it can keep the wine looking hazy by preventing fine particles from settling out.
Degassing is straightforward: vigorous stirring with a long-handled spoon or a degassing attachment on a drill releases trapped gas. You’ll often see the wine foam up as CO2 escapes. Repeat until stirring no longer produces foaming. Properly degassed wine clears faster, tastes smoother, and is ready for fining, filtering, or simply aging in a carboy until you’re ready to bottle.