Secondary Fermentation

Secondary fermentation is where your wine develops character. The violent activity of primary gives way to subtle transformation as remaining sugars ferment, sediment settles, and flavors integrate. Here is how to manage this crucial phase.

What Happens in Secondary

Technically, “secondary fermentation” is a misnomer—it is really the tail end of primary fermentation plus aging. But the winemaking community uses the term universally, so we will too.

During secondary:

• Remaining sugars convert to alcohol (fermentation completes)
• Yeast and sediment settle to the bottom
• Harsh flavors begin to mellow
• Wine clarifies naturally
• Malolactic fermentation may occur (if desired)

The Transfer to Secondary

Transfer wine to a carboy or similar vessel when primary fermentation slows—typically when specific gravity drops below 1.010 for reds (after pressing) or below 1.000 for whites.

Key considerations:

• Minimize oxygen exposure during transfer
• Leave sediment behind
• Fill container as full as possible (minimal headspace)
• Use an airlock—CO2 is still being produced

Headspace Management

Oxygen is wine’s enemy during secondary. A half-full carboy exposes too much surface area to air, promoting oxidation.

Solutions:

• Use appropriately sized containers
• Add sanitized glass marbles to displace space
• Top up with similar wine
• Purge headspace with CO2 or argon

As a rule, keep headspace to the carboy’s neck—no more.

Duration of Secondary

There is no fixed timeline. Secondary lasts until:

• Fermentation is confirmed complete (stable SG for two weeks)
• Wine has clarified sufficiently
• Malolactic fermentation is complete (if conducting MLF)
• Wine tastes ready for bottling or barrel aging

This typically means 4-12 weeks minimum. Many wines benefit from much longer bulk aging.

Monitoring Secondary

Check specific gravity: Should be stable below 0.995 for dry wines. Rising gravity indicates refermentation—investigate immediately.

Watch airlock activity: Occasional bubbles are normal as dissolved CO2 escapes. Vigorous bubbling suggests active fermentation or contamination.

Taste periodically: Wine should taste cleaner over time. Off-flavors that worsen indicate problems.

Visual inspection: Wine should slowly clarify. Cloudiness that persists may need fining or filtration.

Racking During Secondary

Racking (transferring wine off sediment) prevents off-flavors from yeast autolysis (breakdown) and helps clarify the wine.

Typical schedule:

• First rack: 2-4 weeks after transfer to secondary
• Second rack: 6-8 weeks later
• Additional racks: As needed for clarity

Each racking leaves sediment behind and introduces small amounts of oxygen, so do not rack more than necessary.

Sulfite Additions

Add potassium metabisulfite at each racking to prevent oxidation and microbial spoilage. Typical additions are 1/4 teaspoon per 5-6 gallons (targeting 25-50 ppm free SO2).

Test free SO2 if possible—proper levels depend on pH and wine style.