It happened yet again. I bought a red onion for use in salads, only to find that it is sharper and more acrid than even a regular yellow cooking onion. I have tried soaking the sliced salad onions in ice water, even storing them in the fridge that way, changing the water daily. Doesn't help much. Yet the sweet crunch of rings of red onion is something that I look forward to when getting a tuna salad sandwich at Panera. They must go through a lot of onions, and it's always good.
I once explained my problem to a greengrocer, who said that regardless of color, a sweet onion isn't sweet unless labeled that way, and that usually sweet onions are squatter, with flatter poles, than other onions. I've followed his advice but have never had a good red salad onion and rarely are the sweet white or yellow varieties (even Vidalia) as mild as the ones I eat in restaurants. What's the secret?