I can appreciate a good cry, but I do not enjoy it when my eyes get stingy and weepy just because I want to eat an onion. Usually, I wear a pair of cheap lab safety goggles to shield my precious sight orbs, but there’s more than one way to tame an onion. Popping onions in the freezer can decrease the volatility of syn-Propanethial-S-oxide (the compound responsible for your tears), but how long do they need to chill for this move to be effective? Five minutes? 15? A whole half hour?
I had seen conflicting reports on the time required for the cold to be effective, so I bought a bag of small white onions, put them in the freezer, took them out in five minute intervals, and chopped them up to see if the syn-Propanethial-S-oxide had been immobilized. To ensure the test was fair, I used the same knife the entire time, ventilated the chopping area by turning on my kitchen hood in between onions, and made sure my eyes returned to their normal, unweepy state before grabbing the next one. I also wiped down the cutting board and my knife with a wet cloth so there was no lingering onion juice from the previous allium.
The onions that were chopped at five, 10, and 15 minutes stung just as badly as room temperature onions, but after 20 minutes, I was able to make it through to the end of the chopping process before I started to feel anything (my eyes started to get slightly stingy while I was transferring it to a container). After 25, however, I was able to chop and store the whole onion without any stinging whatsoever.
Obviously, not all onions are the same, and the amount of syn-Propanethial-S-oxide will vary depending on your onion’s size, colour, and random growing conditions outside of your control. Yellow onions (which are what I used for this) are usually the most offensive, tear-wise, but I’ve had a sweet Walla Walla give me some grief, and shallots always seem particularly angry, but 20-25 minutes should be enough to decrease the volatility in most of these aggressive alliums. If you’re chopping more than one, take them out of the freezer one at a time so the syn-Propanethial-S-oxide doesn’t have a chance to warm as you chop.