Cutting onions is a notoriously tricky endeavor for any recipe that includes it on the ingredient list. You start by navigating the layers you should peel away and discard (or reserve for a stock recipe later) without going too far and tossing out too much of a good onion. Meanwhile, you’re also trying not to look like you’ve just heard the worst news ever with tears running down your face. It’s a lot to go through for a simple meal, but onions can make all the difference in the flavor of a dish.
That said, you may have noticed that the distinct taste is sometimes less pungent than you thought it'd be. There could be several factors — the amount of onion you’re using, how long it’s cooked, or whether you tossed it in raw — but it turns out that the initial slice of your knife can be what alters an onion’s flavor right from the start.
The experts at Cook’s Illustrated tested out eight white onions that they cut in two different ways: pole to pole (with the grain) and parallel to the equator (against the grain). According to their results, the onions that were sliced pole to pole were noticeably less flavorful in both taste and odor compared to those cut along the equator. If that seems like far too simple a reason for such a big change in taste, you can try testing it out yourself the next time you’re whipping up a meal that requires onions. For those who are skeptical, however, we can assure you that there is science to support the claim.
Onions produce a substance called thiosulfinates, which is where the strong flavor comes from. The potent flavor and odor occurs when that substance reacts with the veggie’s proteins. This happens when the cells are damaged — like when a knife slices through them. When you cut pole to pole, you’re cutting with the grain and therefore causing less damage to the cells. Cutting along the equator and against the grain causes the opposite and more pungent effect to occur.
This can also explain why you might find yourself crying more than other times while preparing a meal with onions. With this info in mind, you can not only customize the overall taste of your meals, but also potentially cut back on the amount of tears you shed.