When mead is transferred to secondary or to the container for bulk aging, does it have to be airtight (well, there should be as little headspace as possible)? Apparently the ancients used olive oil on top of the wine to keep the outside air out -- the idea being that the oil will sit on top of the wine, creating a barrier against outside air... I'm just wondering whether anyone has tried this before and/or whether it's even a good idea...