Grapes want nothing more in their life than to be vinegar. That is their final destination. The job of the winemaker is to halt the process midway and keep it at the wine stage. Sanitation is the key to this, and a big part of keeping out the nasty bugs that will make our wine vinegar (or spoil it in other ways) is to keep every container absolutely full to the brim so there's no room for the nasties to move in and set up shop.
To do this you need a large selection of different sized containers. We're never sure exactly how much of a particular wine we're going to have. We may have a 1500 gallon tank we're planning to fill with this year's Merlot, but we may intially have 1623 and a half gallons. So we'll need our tank, plus 2 60-gallon barrels, plus a 3-gallon glass carboy and a few 1-litre bottles. The selection of available containers at Babcock is as follows: besides our various tank sizes from several thousand gallons down to 120 gallons, we have: 60-gallon (225litre) barrels, 15.5- and 13.5- gallon kegs, 6- and 3-gallon glass carboys, 1-gallon jars, and 1-litre, 750ml and 375 ml bottles (with screwcaps).
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| 60 gallon barrels, then (l-r) 3-gal carboy; 6-gal cb; 375ml btl; 3-gal cb; 13.5gal keg; 1 gal jar; 1-litre btl; 750ml btl; 15.5-gal keg |
So, once we have all of our vessels topped up to the brim, it would seem we could just leave them to mature until bottling, right? Unfortunately, that's not the case. The volume of the wine fluctuates for various reasons, and wooden barrels are the worst culprits.
The wood is naturally porous, so air passes through, and the maturing wine soaks into the wood. This is an integral part of the process and the reason wood barrels are used in the first place. With this process, however, you get evaporation, and a portion of the wine just disappears into thin air. Known as "the angel's share," the losses of barrel-matured wine can amount to about 1 litre/week per 60-gal (225litre) barrel. So if we have a 9-barrel lot of Cabernet, for example, we may be anticipating about 225 cases, total. But, after 18 months of aging, over 40 cases will go to the angels (with all that free wine, you'd think the angels might be more motivated to help out with the weather or grape prices or something else within their jurisdiction!). And those numbers don't include the losses we incur through racking (see last post, "Rack 'n' Roll") or other processes, like filtering. All in all, for any particular lot of wine, we may lose up to 1/4 or even 1/3 of the initial volume, by the time it makes it to bottle.
Sad as it may be to wave "bye-bye" to the angel's share, the task at hand is to keep those barrels--and other vessels--topped up. Most wineries have a schedule for topping up the barrels. Anywhere from once/week to once/month is common. At Babcock, we try to top barrels every second week. At that frequency, when we go to top them, the barrels will often look like this:  with the wine level down about 3/4 of an inch. Ideally, after topping, it will be up into the bunghole so that when the bung is put back in, it will make contact with the wine, leaving no airspace. As well as the porousness of the wooden barrels, other issues come into play with other vessels:
Temperature is huge. Wine actually takes up more space when it's warm than when it's cold. When it comes to our large tanks of our more everyday wines, we constantly have to monitor where the fill level is and adjust accordingly. If we're cold-stabilizing, for example, (refrigerated jackets on the tank cool the wine down to almost freezing for about 2 weeks), the wine is going to shrink up, leaving a big headspace in the tank, which we'll have to top up. Following this, we may heat the wine (to over 60 degrees F), using the jackets, in preparation for bottling. Now, we have to deal with the wine expanding and maybe overflowing from the top of the tank. If we're not using artificial heating or cooling, we have to deal with this same issue due to weather conditions. At the height of summer, tanks may regularly overflow, no matter how many gallons you take out to try to even things out. Several days ago, we racked a tank that had been cold stabilizing (refrigerated) and put it in a tank outside to warm up before bottling later this week. As always, we filled the tank to the brim. A couple days later, it was burbling out through the top. We know it's going to increase in volume, but we don't know how much, so, out of the 5,000 gallon tank, we removed about 10 gallons, hoping that would be enough. A few days later, it was spouting out the top again, so we had some losses there.
As disheartening as it is to see over-rambunctious wine spilling out from the top of the tank, it's truly heartbreaking to see the glass carboys succumb to the weather. The outside tanks have to deal with the elements as best they can, but within the barrel room, we hope for better. For the most part, the room stays at a nice cool temperature, and the barrels, being wood, are not so susceptible to temperature fluctuations. The glass carboys are a different story. Like everything else, we want to keep them topped right up. A rubber bung goes into the top and we keep it tight, tight so no air can get in, but still, the volume can fluctuate. At best, the seal between carboy and bung will look like this: 
Sometimes, on a hot day, our nicely topped up and tightly sealed carboys will get too warm and break because of the pressure of the expanding wine. That's a real heartbreaker when you hear that "crack!" from out on the crush pad and rush in to see the wine puddling out from around the crumpled carboy, like a gunshot victim. Often it's one of our best wines that may sell for $50/bottle. It's sad to see a 6-gallon carboy go down like that, when there's nothing you can do but watch $1500 go, literally, down the drain in a matter of minutes.
Most winemakers, I think, very wisely refrain from thinking of the wine as a saleable "product" until it's actually in the bottle. Otherwise, between the angel's share, racking and filtering losses and the vagaries of the weather, they may have cause to weep on a daily basis. Much better to think of it as just the cost of doing business.
Joke of the day: a winejob website had a listing written by someone for whom English is not their first language. They were looking for a winemaker without a "pre Madonna attitude." LOL. So, no Elvis impersonators, I guess?
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