Diluted wine of fruity wine? Must concentration – what should or should you not do? Boil the must in a vacuum?

If it rains just before the harvest you risk getting a diluted must. The grapes suck up the water and becomes inflated with water. there are several techniques for what is called must concentration. The most commonly used (but not overly common) in France is probably reverse osmosis (click for photos). You can also use cryo-extraction (freezing the grapes).

A third method is to boil the must in a vacuum, vacuum extraction (but it certainly is not a cheap way of doing it). The process implies that you pump the must through a vacuum chamber, at rather low temperature. At low pressure a liquid boils at a much lower temperature. You can even do it at below room temperature if pressure is low enough. Since the evaporation is done at a low temperature only the water is lost, is the thinking. What remains is a more concentrated must. The unwanted water is gone. (Usually only a part of the must is treated and then blended back into the rest of the must in appropriate proportion.) As a result you get a more concentrated, less diluted wine.

This is originally an Italian invention and we have seen such vacuum concentration machines in Italy and in Austria. We recently asked a producer in northern Italy if it really was allowed to use it in his (illustrious) appellation: “Um, well, no in principle it is not allowed. But we are allowed to chaptalise (add sugar to the must to increase the alcohol). So if instead of chaptalisation I use vacuum concentration, and thus raise the sugar contents with the grapes' own natural sugar instead of extraneous sugar, is that not better?” was his answer. Italian logic? As for France we don’t know if it is allowed or not, but we’ve never seen such a machine here. (On the other hand you don’t often see a reverse osmosis machine either even though it is relatively frequently used at major chateau in e.g. Bordeaux.)

Another person who uses the vacuum machine, and talks warmly about it, is Ken Wright at Ken Wright Cellars in the Williamette Valley in Oregon. It rains a lot in Oregon and Wright is happy with the improvement he gets from the machine according to this interview in Gizmodo: We Must Boil This Wine To Save It. But many people who argue for “natural” wines or “organic” wines will get goose bumps if they see it in a wine cellar. They would consider it “unnatural” to treat a wine (must) like that. (One could of course argue that ‘appassimento’ – partially drying the grapes for an extended time period of time – that is used e.g. to make amarone is just another type of must concentration technique.) It is a difficult question of course: Is it better to use vacuum (or cryo-extraction, or reverse osmosis) to “save” a wine, or is it an unnatural way to treat it that will rob the wine of its soul and character? What do you think?