Disclaimer - although I have a couple of small barrels, I've never
done fermentation in them.
I just use them for aging my reds.

I think barrel fermentations are often done with the head removed from
one end, to allow more room for foaming, etc. I suppose with a white,
being just juice, you could leave the heads on and allow the CO2 to
escape through the bunghole. For reds, I don't see how you could get
all the skins, etc. into the barrel through that little bunghole, or
how you would punch down the cap if you could. OK, so if you haven't
removed a head, I'm guessing you are doing a white wine (Chardonnay?).

Either way, you are looking at maybe a week or so of fermentation,
with the release of lots of CO2. I don't think that puts you at
significant risk for spoilage. Once fermentation is over, you will
want to fill the barrel and keep it topped up.

If you are going to fill it with the white wine, keep in mind that a
new barrel can impart a whole lot of oak flavor in a short period of
time, particularly the smaller sizes. Check it every couple of weeks,
after the first month, unless you are aiming for "Chateau Plywood."
For a barrel of that size, I don't think you'd want to expose even a
very oaky Chardonnay to it for more than a few months, so it would be
a good idea to have a plan for what you are going to do with the
barrel when you empty it. You can fill it with another wine (assuming
you have that much) or burn some sulfur inside the barrel
periodically, to discourage bacteria from growing on the inside.


Doug