Originally posted September 24, 2010
Lot’s of chemistry, that’s what!
September 24, 2010
Since I am driving up to Napa Vally, CA tomorrow for a wedding this weekend, I thought I’d put together a little piece on one of my all-time favorite things: WINE!
It’s red, it’s white, it’s sweet, it’s dry, it’s all basically crushed grapes! Fermentation by yeast converts the fruit sugars into alcohol and voila: a tasty beverage that makes you feel great while you drink it and probably not-so-great the next morning.
Wine has been reported to have originated around 6000 BC in the areas now known as Iran and Georgia and was introduced to Europe around 4500 BC. (http://en.wikipedia.org/wiki/Wine). In 2008, the Wine Institute reported 284 million hectoliters (7.5 billion gallons) of wine were produced worldwide and in 2009, California alone shipped out approximately 470 million gallons!!!
So what’s actually IN wine?
According to Prof. Andrew Waterhouse at UC Davis, it’s 85% water, 12% ethanol (alcohol) and 3% “other stuff”. In red wine, that “other stuff” is mostly glycerol, acid, phenols, sugar and minerals (with a sprinkling of amino acids, sorbitol, esters, and sulfites).
Image credit: Waterhouse Lab
But don’t be scared off by those chemicals! Let’s look at a few…
Glycerol is a natural product of yeast fermentation and is effected by many factors including grape ripeness, microbial flora, temperature and the yeast strain. Glycerol is often thought to affect the “mouth-feel” and textural properties of a wine and thus a higher glycerol content improves the quality of the wine. However, there’s little chance that the amount of glycerol in a glass of wine could produce a viscosity change discernible to the human pallet. (Christin Carlson, Waterhouse lab, 2004)
The pH of wine is often between 3.6 and 4 (pure water is pH 7) and this acidity can affect the taste of wine as it contributes to its “tartness”. Most fixed acids found in wine originate with the grape itself and are mainly tartaric, malice and citric. (Doug Nierman, Waterhouse lab, 2004)
Polymers (long chains) of phenols are called tannins and come from the grape skins making them more prevalent in red wine than in white. They are often thought to relate to flavor (you’ve probably heard the word tossed around by an enthusiast), but according to Dr. Roger Boulton, scientific evidence is lacking. Most flavors come from a specific molecule-receptor interaction, but tannins simply coat the tongue by non-specific binding. This is what leads to the “clarity” of a wine.
Wines get their tannin content from the skins!
Sulfites are present in ALL wines due to the fermentation process, but are often added to prevent oxidative damage or to stop the fermentation process at specific stages. There is a lot of incorrect information regarding sulfites, but here are a few interesting facts: approximately 1,000 milligrams are produced by the human body daily and there are about 10 milligrams in a glass of wine. There is typically a higher concentration in white vs. red wine and even more in sweet white wine. Some people have sulfite allergies but there is no evidence that sulfites cause headaches.
As much as I love wine, this little post doesn’t do justice to the complexity of flavor and texture stemming from the chemistry and art of winemaking. But now that your palettes have been whetted, check out this article from the Chemical Heritage Foundation for a more thorough (and fun) read on the chemistry of wine flavor.
Cheers!
~gk