Should I top my barrels regularly?
The short answer is: No. Only top when you open the barrel, for instance when you sample or rack.
But, but, but won’t the wine be ruined by the air in the headspace if I don’t top regularly?
No, there is no oxygen in the headspace that forms in a sealed barrel.
“The ullage that develops over the wine as liquid escapes through the wood is not a source of spoilage. It contains no oxygen.
“Thus, filling the ullage space (topping) is necessary only when air enters the barrel during wine sampling or racking.
Only with very long aging, as in brandy, is it likely that the ullage will become sufficiently large that the wood above the space will dry. During drying, shrinkage of the wood will permit the ingress of oxygen. Even here, this is most likely to be between, rather than through, the staves.”
Ron S. Jackson
Wine science: principles, practice, perception
This concept, that the head space above the wine in the barrel, is not “air” and does not contain oxygen and does not spoil the wine, an be a tough one to wrap your head around.
Here’s how it works…
Liquid wicks its way out of the barrels through the staves by the force of capillary action, the same way water wicks its way up to the leaves on top of the tallest trees.
In a barrel sealed by a bung this wicking action creates a forceful vacuum, which, at first, compresses the barrel itself. After the barrel is compressed to its maximum extent, air is then drawn into the barrel and into the wine by the force of the vacuum. Once this vacuum is formed, air is drawn into the barrel at a constant rate, regardless of the level of the wine inside the barrel.
The air that is drawn into the barrel percolates through the wine in a process called “micro-oxygenation.” (Micro-ox does all sorts of beneficial things to yourbwine, which is a whole ‘nother topic in itself.)
During this micro-ox process all the oxygen in this incoming air is bound-up bythe wine and/or the SO2 in the wine, which leaves only the non-bound, non-oxygen, gases remaining to form the headspace in the barrel.
Therefore, the headspace in a sealed barrel contains no oxygen and does not cause wine spoilage. In fact, when you top, you introduce air/oxygen into the headspace.
So when you do open a barrel for sampling/racking, make sure you top up the barrel to the very tip-top of the bunghole such that wine spills out when you insert the bung. That way you know there is no air/oxygen remaining from when you opened the barrel.