You fill your barrel, pop the bung back in, and check on it a few months later. The level has dropped noticeably. Nothing is leaking. Nothing looks wrong. Where did the wine go?
The answer has a beautiful name: the angel's share. It's completely normal, it happens to every barrel in the world, from the great cellars of Rutherglen to your garage, and understanding it is one of the most important things a home barrel owner can know.
What is the angel's share?
Oak is a porous material. As your fortified wine sits in the barrel, a small amount of water and alcohol vapour slowly passes through the staves and evaporates into the surrounding air. This is not a fault or a failure. It is the mechanism by which barrel ageing works. The slow exchange of oxygen through the wood is what transforms raw fortified wine into something layered, complex, and deeply aged.
The wine that evaporates has been whimsically described as 'going to the angels', hence the name. In the great whisky distilleries of Scotland, the angel's share can amount to 2% of a cask per year. In the warm, dry conditions of Rutherglen, home barrels can lose significantly more, usually around 3 to 5% per year, depending on the conditions.
How much should my barrel be losing?
This varies based on several factors, but as a general guide for home barrels in Australian conditions:
- A 5 litre barrel can lose 0.5 to 1.5 litres per year, up to 30% of its volume in a warm environment.
- A 10 litre barrel typically loses 0.5 to 1 litre per year.
- A 20 litre barrel might lose 1 to 2 litres per year.
- A 50 litre barrel typically loses 2 to 3 litres per year under normal conditions.
If you're losing significantly more than these amounts and can't attribute it to a hot summer or extremely dry storage conditions, it's worth checking for a slow leak around the bung or staves. Our guide to fixing a leaking barrel covers exactly what to look for and how to address it. And if you're still deciding on barrel size, our guide to choosing between 5L, 10L, 20L, and 50L explains how size affects evaporation rates and overall management.
What affects how quickly your barrel loses wine?
Temperature
This is the biggest factor. A barrel in a hot summer environment will lose wine much faster than one in a cool, stable environment. At Stanton & Killeen we actually embrace this. Our barrels experience hot summers (45+ degrees) and cool winters in Rutherglen (-3), and that variation contributes to the complexity of the wine. But it does mean you'll need to top up more frequently during summer months.
Barrel size
Smaller barrels have a higher surface area relative to their volume, which means they lose a higher proportion of their wine to evaporation. A 5L barrel ages wine faster and loses proportionally more than a 50L barrel, which is one reason smaller barrels suit owners who want faster development, but require more active management.
Humidity
Very dry conditions (low humidity) accelerate evaporation. Very humid conditions slow it. A barrel in an air-conditioned room will behave differently to one in an open garage or undercover outdoor area.
Age of the barrel
Brand new oak is more porous than well-seasoned, older oak. A barrel that has held wine for several years will typically lose less to evaporation than a brand new one in its first season.
When does evaporation become a problem?
Evaporation itself is not a problem; it's part of the process. The issue is when the level drops low enough to create significant ullage: the air gap between the surface of your wine and the bung hole.
Ullage increases the amount of oxygen your wine is exposed to. A small amount of controlled oxygen exposure through the oak staves is beneficial. Significant ullage from a large air gap accelerates oxidation beyond what you want and creates conditions where spoilage bacteria can thrive.
The rule of thumb: top up before your barrel reaches three-quarters full. For smaller barrels in hot conditions, this might mean topping up every two months over summer. For larger barrels in stable conditions, every six or twelve months may be sufficient. If your barrel has already been sitting low for a while, our post on what to do if you haven't topped up in months walks you through exactly what to do, in order. For a deeper look at ullage and how much is too much, our guide to ullage in home barrels has everything you need.
What to top up with
When you top up, you're adding new wine to replace what's evaporated. The wine you choose has a real impact on your blend, so it's worth thinking about rather than just using whatever's available.
For a mature barrel, you'll generally want to top up with a wine of similar age and style to what's already in your barrel. Adding a large amount of young, fresh fortified to an older barrel can dilute the aged characters you've spent years building: the rancio notes, the complexity, the warmth. Liquid Luxury offers topping wines across the Muscat, Topaque, and Tawny styles at different age points, as well as 250ml sample bottles so you can bench trial before committing to a full top-up. Our guide to choosing the right topping wine covers the full range and helps you match the right wine to where your barrel is right now.
Frequently asked questions
My barrel level dropped a lot over summer — is something wrong?
Almost certainly not. Summer evaporation in a warm Australian environment can be dramatic, particularly for smaller barrels. If nothing is visibly leaking and the level drops over summer and stabilises in cooler months, that's normal. Just top up before it gets too low.
Can I slow evaporation by storing the barrel in a cooler spot?
Yes. Cooler, more stable temperatures mean slower evaporation and slower overall ageing. Whether that's desirable depends on your goals. Many experienced barrel owners prefer a naturally warm and cool environment because the seasonal variation builds complexity. At Stanton & Killeen, our barrels sit in large sheds that hit 45°C in summer and we consider that an asset, not a problem.
Does the alcohol or the water evaporate more?
Both evaporate, but in conditions typical of Australian home environments, warm and relatively dry, water tends to evaporate faster than alcohol, meaning the alcohol percentage of your wine will actually increase slightly over time. In cooler, more humid conditions the reverse can happen. This is one reason annual sample analysis is valuable: it tracks these changes so you know exactly what's happening in your barrel.
What if my barrel loses wine much faster than the estimates above?
Check carefully for a slow leak around the bung, tap, or between staves. A small drip can lose considerable volume over weeks without being obvious. If you can't find a leak and the loss seems excessive, contact us. It could indicate a crack or loose hoop that needs attention