You ferment 5,000 gallons. You bottle 4,100. The gap isn't a spreadsheet error. It's real money, walking out through barrel seams, pump housings, and the air itself. At $40-60 per bottle wholesale, that loss is substantial. And if your records don't match what TTB expects, that gap triggers the audit.

Understanding wine losses isn't glamorous. But it's one of the highest-ROI operational conversations a winery can have. Most US winemakers know that losses happen. Fewer track where they happen, or prove it to regulators.

The TTB Accountability Requirement

The Alcohol and Tobacco Tax and Trade Bureau (TTB) requires bonded winery premises to account for all wine volumes monthly. The Report of Wine Premises Operations (TTB Form 5120.17) asks for:

Opening inventory by tax class
Wine produced (fermented)
Wine received from other premises
Wine removed (bottled, tax paid, exported, for laboratory use)
Wine lost (by category)
Closing inventory

The "wine lost" line is where compliance meets reality. TTB recognizes normal losses from evaporation, racking, filtration, and standard production, provided they are documented and fall within regulatory thresholds. Under 27 CFR 24.266, normal losses up to 3% of aggregate inventory or 6% of produced wine are permitted without filing a specific loss allowance claim. Large unexplained discrepancies, especially if they repeat, trigger focused audits on whether excise tax was assessed correctly on all wine leaving bond.

Where Wine Actually Goes: Five Loss Streams

Barrel evaporation ("angel's share"): This is the known quantity. In Napa and Sonoma's warm, dry growing seasons and barrel cellars, annual evaporation rates typically range from 2-5% per barrel, depending on cellar climate control and humidity. Underground caves substantially reduce evaporation. A standard 60-gallon barrel holds 227 liters. At 5% annual loss, that's 11.4 liters gone. Scale that across a 500-barrel program: 5,700 liters (7,500 standard bottles) lost each year to air alone.

5,700 liters / 500-barrel cellar at 5% evaporation annually

Real cost at $50/bottle wholesale: $375,000/vintage

Tank and fermentation losses: Open-top fermenters lose measurable volume during red wine punch-downs and circulation. Even sealed stainless tanks breathe through valves. Floating-lid fermenters reduce but don't eliminate the loss.

Racking and settling: Each racking—from gross lees (pre-fermentation whites), to post-fermentation yeast separation, to fining—leaves wine in the lees. Successive rackings on a white wine from juice-settling to stable finished wine typically result in 5-10% loss of the batch volume.

Filtration absorption: Cellulose pads, crossflow membranes, and diatomaceous earth all absorb or suspend wine. High-volume bottling lines with multiple filtration stages can lose measurable volume to these steps, though exact percentages vary by equipment and winemaking approach.

Line and equipment retention: Hoses, pump bodies, filter housings hold residual wine after each operation. Fifty-plus transfers per vintage means a meaningful cumulative figure. Most wineries don't measure this, which is exactly why it surprises them at month-end.

California: Scale and Extremes

California produces over 80% of US wine. Three regional loss drivers stand out:

Heat and evaporation intensity: Napa and Sonoma valley summers are warm and dry, particularly during harvest (August-October) and early barrel aging. Peak summer temperatures can reach 95-100F or higher on warm days, though average conditions are more moderate. Without climate control, evaporation rates are significantly higher than in cooler regions. Many Napa operations invest in underground caves specifically to manage evaporation economics and maintain steady cellar conditions—and it's a profitable investment.

Seismic risk in planning: California's earthquake risk means barrel stacks can fall and tanks can crack. This is primarily a safety issue, but it has a volume dimension relevant to TTB reporting and loss reserves.

Custom crush complexity: Crush facilities processing fruit for multiple winery clients must track losses by lot and client, not aggregate them into a facility-wide average. One client's loss is another's unbilled cost.

Finger Lakes and East Coast: Different Pressures

Eastern US wine regions (Finger Lakes NY, Shenandoah Valley VA, Willamette Valley OR) operate in wetter, cooler conditions than California.

Barrel evaporation is lower, but the risk profile shifts:

Humid cellars reduce evaporation but increase mold risk on barrel exteriors and bungs, compromising wine quality and creating non-recoverable loss.
Non-climate-controlled summer heat can drive volatile acidity and Brett spoilage in barrel, turning volume into unsellable wine.

The lesson: match cellar practices to your specific region's humidity and temperature profile. California benchmarks don't transfer.

Tracking for Compliance and Cash

TTB requires documented losses. Your system must provide:

Monthly opening and closing inventory by tax class
Records of all wine produced, received, removed, and lost each month
Ability to categorize losses by type (evaporation, racking, filtration, other)

At small scale (under 5,000 cases/year), a well-maintained bound ledger or spreadsheet works. At scale (multiple tax classes, lots, clients, or a custom crush operation), manual systems fail. You can't reliably reconstruct cellar activity from notes at month-end, especially under audit pressure.

Digital cellar management systems that capture every vessel movement and volume change automatically feed TTB monthly reports. Instead of reconstructing activity, you select the date range and export. Data accuracy improves; compliance prep time drops from days to minutes.

What "Normal" Looks Like

Documented loss ranges for US wineries vary by climate and winemaking approach:

Annual barrel evaporation: 2-4% (climate-controlled), 3-5% (ambient conditions)
White wine racking losses: 5-10% from juice to stable wine
Racking and filtration combined: Typically 10-15% cumulative from juice to finished wine

Keep in mind that these are guides, not fixed targets. Your actual losses depend on your cellar climate, equipment, and practices. TTB's regulatory framework (27 CFR 24.266) sets the thresholds for when you must document and justify excess losses, but the agency recognizes that well-managed wineries will have normal operational losses within documented ranges.

A California winery that tracks and documents its losses accurately can defend those figures to TTB. A winery that loses track of the numbers faces audit risk and potential tax exposure.

The cost of accurate cellar records and reasonable loss management is a spreadsheet. The cost of not having them is substantial.

Ready to close the gap? Cepaos tracks production volume and loss categories in the structure TTB expects. Monthly compliance reports generate themselves. Try Cepaos through our founding members program.