I spent most of the last week on the road, making stops in New York, Portland, and Seattle. At each stop, I found myself confronted with tasters whose first action upon reaching my table was to pour water into their tasting glasses so as to rinse out whatever was in the their glass and start "fresh". I've always hated this practice, since at best, you dilute the wine, and at worst you change its flavors, often dramatically, with chlorine or other minerals that were in the water. So when I got back to the vineyard this week I asked Winemaker Ryan Hebert if he could figure out how much the residual water left in a glass after a rinse actually dilutes the wine you pour in. It's more than you'd think.
To answer the question, Ryan mimicked what we typically see at tastings: where a taster pours water into a glass, swirls it around a bit, and then dumps it, holding it upside down for about a second. That's pretty much normal; some people are more rigorous and shake their glass to the extent that I worry the stem will snap, while others don't even empty the water fully. Then, he measured the difference in the wine's alcohol levels with and without the water. What he found was that in a one-ounce pour, the alcohol level is reduced by 6.9% thanks to the water in the glass. That means that to your ounce (29.6 ml) of wine you've added 2.1 ml of water, diluting a wine that is 13.5% alcohol nearly a full percent to 12.6% and weakening all the other flavors similarly. Calculated another way, we would get the same effect by pouring roughly eleven gallons of water into each ton of grapes.
Do you think that this impacts the taste? You bet. And it impacts the texture more, thinning out a wine and shortening its finish. This all happens even with distilled water, which is free of mineral content. Using mineral water, filtered water, or tap water can have even more unpredictable effects. We tried the same experiment with filtered water and found that the high mineral content dropped the amount of malic acid in our sample (the 2011 Picpoul Blanc) from 0.21 grams per liter to 0.08 grams per liter, presumably because the acids in the wine bonded with the basic particles in the mineral-rich water. And I've seen people rinse with water that was so chlorinated that I can't imagine the wine tasting remotely like it was intended.
So, what should you do at a wine tasting? First, don't feel that you need to rinse at all, unless you're trying to get an unusually strong flavor out of your glass, or you're moving back from red to white. Remember that most wine tastes -- and is structured, from a chemical standpoint -- a lot more like most other wines than it does like water, so the little bit of Chardonnay you have in your glass is going to impact your next taste of Syrah much less than an equivalent amount of water would. And if necessary, try to rinse your glass out with a little of the wine that you'll be putting into it next. It doesn't take much, and the winery representative who's pouring the wine will likely be pleased that you care enough to taste the wine properly. You'll make your pourer even happier if you make it clear in advance that you'd like a rinse... it's always sad when you present a full pour of a scarce wine just to see the taster swirl it around, dump it out, and hold their empty glass back out at you.