While it has always been my goal to make top notch wine, truth be told, many vintners already do that very well.  My main interest in grapegrowing and winemaking has been to tinker with some ideas that, if proven out, could result in a general improvement in our product.

One of the ideas I’ve been playing with for a number of years now is submerged cap fermentation.  First, some background:

When making red wine (whites are different), the grapes are crushed and then the resulting mixture (the “must”) goes into some container, usually a tank but sometimes smaller vessels, where it ferments.  At some point either during or after completion of fermentation, the must is pumped from the tank to a “press”, which squeezes out the juice/wine from the skins, which are then discarded.

The grape juice itself is pretty innocuous stuff, really just a solution of water, sugar, and tartaric acid, plus a few other things in very small amounts.  What makes red wine the wonder that it is comes from the skins.  During the fermentation, the good stuff in the skins leaches into the juice.  If it weren’t for this, red wine would really end up more like rosé than red wine.

If, once the grapes were crushed into must, the skins just naturally stayed submerged in the juice, all would be good.  Unfortunately, that’s not what happens.  Once the yeast get going, they convert the sugars in the juice into two main things, alcohol and carbon dioxide.

As the yeast give off the carbon dioxide, the skins, which create a semi-impervious barrier, keep a good deal of the carbon dioxide captured beneath it.  Like an umbrella in an updraft, the skins (which together form the “cap”), rise up.  As a fair approximation, this uplift is enough that half the cap is above the juice.

This creates two problems:  first, if you’re trying to get the goodies out of the skins, and half of them aren’t in contact with the juice, you’re only getting half of the goodies out.  Second, the part of the cap floating above the juice is subject to microbial infection, which can create all kinds of problems down the road.

So two main methods of dealing with this problem are used.  The most common, particularly in larger, tank, fermentations, is called the “pump over”.  As it’s name implies, you pump the juice over the cap to keep the cap wet and get contact between the juice and the skins.  During the height of fermentation, I try to have 3 daily pump-overs, each lasting 20-30 minutes.  The second, more often used in smaller fermentations, is called the “punch-down”.  Again, as it’s name implies, a tool of some sort is used to push the cap down into the juice.

Without getting into the claimed advantages and disadvantages of each method, both methods do not come close to maintaining 24/7 contact between the skins and the juice.

A third, and much less used, method is called submerged cap.  This involves using some sort of screen that mechanically keeps the cap totally submerged. When I tried to find out in the literature about how it compared with the other two methods, I couldn’t find much.  (If someone thinks there’s some good resources on the subject out there that I missed in my search, I would appreciate your dropping me an email.)

So I decided to try out submerged cap fermentations on my own.  My results on Friday.

This entry was posted on Monday, November 2nd, 2009 at 7:34 am and is filed under Winemaking. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.