(WBlakeGray) - Nobody knows for sure what causes red-wine headaches. I heard an intriguing theory last month while interviewing a chemist-turned-winemaker, and it fits the facts as we know them.

Here's what we know:

* Many people get headaches from red wine, but not white wine

* Sulfites are not to blame. Some people are allergic to sulfites, but headaches are not an allergy symptom, and besides, white wines have more sulfites on average than red wines.

* Some people report that they don't get headaches when drinking red wine in Europe, but they do in the US.

* Some doctors say the first thing you should consider is the alcohol itself, as it can cause headaches. Because alcohol level is such an emotional issue these days, that's an appealing theory, but I have always gotten comments from people who say they can drink vodka (40% alcohol) without headaches, but not Zinfandel (15-17% alcohol). 

* There has never been a conclusive medical study about red-wine headaches and you won't find a reputable doctor anywhere who can tell you exactly what the cause is. All we have is speculation.

Which leads me to Chris Howell's theory.

Howell is the winemaker for Cain Vineyard & Winery on Spring Mountain in Napa Valley. He studied winemaking in Montpellier in southern France and worked at Chateau Mouton-Rothschild before coming back to the US in the 1980s.

Howell says that he gets red-wine headaches, inconvenient because Cain makes only red wines, and also because he's a tremendous wine lover who likes to splurge on the great red wines of Europe.

He also says he can smell a wine and tell whether or not it will give him a headache. (Cain's wines don't, he says.)

To understand Howell's theory, you need to understand the basics about how grapes become wine. Yeast, a single-cell organism that lives everywhere, consumes the naturally occurring sugar in grapes and excretes alcohol. At high enough levels, alcohol kills everything, including the yeast that creates it, so as the alcohol percentage of a vat of fermenting grapes rises, the yeasts die off little by little.

There are many, many kinds of yeast. In theory, over time the yeasts that live in a vineyard (and winery building) adapt to its grapes in a symbiotic relationship. These yeasts convert all the sugar in the grapes to alcohol, run out of food, and die.

However, most modern wineries use yeast they buy in plastic bags. They do this for a variety of reasons. No. 1 is reliability: different yeasts can create different flavors in wine, including some that some consumers might find disagreeable. Some wineries use "commercial yeast" specifically to get desirable flavors.

Another reason wineries use commercial yeast is that some yeasts tolerate alcohol better than others and can live at higher levels of it. This is important if grapes are very ripe and have a high sugar content. The winery doesn't want all its yeast to die, or some sugar will be unconverted and the resulting wine may be too sweet. (This is how most dessert wines are made.)

Howell's theory is this:

Just like people, yeasts work differently under stress. A high-alcohol environment is stressful for yeast. Howell believes some yeasts create different chemical compounds when dealing with the amount of sugar and alcohol in very ripe grapes, and these compounds cause red-wine headaches.

It's just a theory, but it fits the facts as we know them.

* White wines are usually lower in alcohol than reds so the yeasts would be less stressed

* Not many European wines are made from grapes as ripe, and thus high in sugar, as grapes get in California.

* People report getting red-wine headaches from inexpensive U.S. wines that have alcohol under 14%, the same as European wines. However, that may have been achieved (for the purpose of paying lower tax) by having the alcohol reduced mechanically, through reverse osmosis or spinning cones. If that is the case, some alcohol would be removed but the headache-causing compounds would stay in.

* This would explain the no-headache-from-vodka conundrum. It's not the alcohol itself; it's what it does to the yeast.

It's worth noting that most doctors will point out that your stress is a factor in headaches. You don't get red-wine headaches in Europe because you're on vacation.

That said, if you want to drink red wine without a headache, "take a plane to Paris" isn't a great solution. But Howell's theory gives a promising avenue.

It's worth trying wines of lower alcohol but ONLY in cases where you know something about the winery. You can't just go by the alcohol percentage on the label. You'd want to know that the winery uses "native yeast fermentation;" in other words, it doesn't use commercial yeast.

Unfortunately there's no "safe label" to read about this. Wineries don't have to tell the truth about what yeast they use. Plus, as every winemaker who reads this will comment if I don't say it, last year's yeast can live in the winery over the summer and survive to ferment this year's wine.

Moreover, we don't know what percentage of alcohol is "lower alcohol." Cain's wines are generally a little above 14% alcohol, low for Napa Valley but higher than you might find in some parts of the world. I would argue that "low for Napa Valley" is what's important. The yeast in Cain's vineyard could be well adapted by now to the sugar levels that the grapes are harvested at. Cain's yeast would be unlikely to have trouble at a sugar/alcohol level that yeast in Germany or Austria might struggle with.