Expansion in the Carboy

updated 03/17/2024

Last night I racked 4 liters of Cabernet Franc, as I needed topup for the barrel. The plan was to take a tasting sample from the barrel and the topup wine for comparison, topup the barrel, and put the remainder into 750 ml bottles for later topup. I use #3 silicon solid stoppers for the bottles.

Note: The wine in question is long past fermentation and has been degassed, and while the temperature in the cellar has seasonal changes, it doesn’t change rapidly, day to day.

All went according to plan. I filled four 750 ml bottles and inserted the #3 stoppers in the first two, leaving 1/4″ (0.6 cm) above the bottle rim. This is plenty for extraction.

The third one went nearly flush in the bottle, as the inside diameter of the bottle is apparently a bit larger. There is enough outside the bottle to extract it.

The fourth one was even larger inside, and I incautiously buried the stopper:


I considered my options:

  1. Use a corkpull. However, that will scar the outside of the stopper, destroying it.
  2. Use a corkscrew. If I don’t drive all the way through the stopper, it may still be useful.
  3. Use physics.

Upon reflection, I went with option #3.

There is a 10 degree F difference in temperature between my cellar and my kitchen. I put the bottle on the kitchen counter and left it for an hour.

The wine and air in the ullage warmed up, expanded, and blew the stopper out of the bottle. Problem solved!

Something to consider with bulk aging is the amount of headspace. I read advice where it’s recommended to fill the carboy to within an inch of the stopper. Unless the temperature and barometric pressure are very constant, this is a bad idea. Changes in either can cause the wine to expand and flow into the airlock or vented bung.

In the following photo, there was 1-1/4″ (3.2 cm) headspace two months (January) ago. Since that time the average temperature in the cellar has risen 4 degrees F, and now the wine is touching the stopper.

This wine needs racking, so I’ll lose some volume. But post racking, I’ll leave 2″ headspace, as we’re coming into summer months and the wine will expand more.

How much headspace is enough?

That depends on the container. There’s no “one size fits all” answer. For 19 and 23 liter carboys, I typically have 2″ to 3″ (5.0 to 7.6 cm) of headspace. For smaller containers, I will use 1″ to 2″ (2.5 to 5.0 cm). For 375 ml, 750 ml, and 1.5 liter bottles, I fill to the base of the neck (for Bordeaux style bottles) or whatever a filler tube leaves for space.

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