Alicia Armentia of the Rio Hortega Hospital in Valladolid, Spain, and her colleagues treated five people who had developed severe allergic reactions after drinking either wine or grape juice. Three of the patients had facial flushing and swollen lips, while another experienced asthma-like symptoms. The fifth patient developed anaphylaxis, a whole-body allergic reaction that can cause death as a result of constricted airways.

Armentia and her colleagues successfully treated all of these patients, but they remained baffled over the cause of the allergic responses. A battery of tests on the patients ruled out the most likely suspects, such as egg white, which is sometimes added to wine to clarify it and reduce harshness, and grape extract.

More elaborate analysis of the patients’ blood revealed antibodies suggesting a recent bee or wasp sting. However, none of the patients reported being stung.

Grapes of wrath
So the doctors looked for allergic responses to red and white grape juice, along with a newly pressed wine and three aged wines, all from different vineyards.

Both types of juice and the freshly made wine all triggered reactions in blood samples taken from the patients. Further chemical tests provided strong evidence that this was due to trace amounts of venom from yellow-jacket wasps – not from bees – in the beverages.

“It’s likely the insects fell into the grape juice when the grapes were pressed,” says Armentia.

Wasps abound on grapes in late summer, explains Lee Townsend, an entomologist at the University of Kentucky in Lexington, Kentucky, US. “They will come to anything that’s overripe, because they’re running out of food by this time of year,” he says.

Armentia suspects the aged wines did not produce an allergic reaction in the blood tests because any venom proteins they might have contained would have degraded as the wine matured. Even a few weeks’ ageing probably breaks down the venom enough that the risk of a dangerous allergic reaction is minuscule-but if they want to be on the safe side, people with bee and wasp allergies may want to avoid drinking freshly made wine, she adds.