There’s this moment: You’re making a recipe that requires one big onion, and so you reach into the crisper and pull out what seems like a clear candidate, only it turns out to be clearly medium, and the meal goes limp. Been there? Done that? Guilty as charged? But it’s not the recipe’s fault, really. It’s the onion’s.
Not all onions is created equal. In fact, the commercial world sort them with very precise methods. If we don’t pay attention, the results can be woody or watery in our own cooking. The above infographic explains the difference between the seven grades of fresh-market-size onion, from pearl to colossal. (And no, a pearl onion isn’t just small (it’s very different in structure), too.)
Onion Sizes for Cooking
From there, the grading system starts very small. There’s the tiny speck to maybe inch-and-a-half-size boiler size and then there are the pearl onions. And while most home cook dismiss them as just pickle material, that’s where we’re missing out. Because the cell structure of those little bulbs is tighter, they hold up well when cooked; they don’t fall apart in your stew like a bigger onion will. Want an onion that won’t turn to mush after an hour in a braise? Smaller grade all the way.
The chart maps diameter to use, and points out that boiler onions are best for stews and whole cooking. Why? It’s a textural thing: the larger the onion, the higher the water content and the thinner the wall, great for caramelizing but lousy for standing up in a soup.
And then there’s the little guys: the medium-to-small stuff. This is what you’re buying most of the time; this is the onions-onions. A typical saute base is an eight-ounce onion which is basically a medium. It has enough bite but also some sweetness, and it’ll melt right into your sauce. But the bigger ones gets sweeter (and milder), since they’ve had longer to build up their sugars. A “super colossal” can reach twenty-eight ounces, and will be noticeably sweeter and less pungent then its smaller cousins. No wonder they’re reserved for being sliced into burger rings, or bloomed in a bit of batter.
You don’t need a mild, sweet onion mincing up a salsa, any more than you’d need a sharp, pungent pearl onion roasting whole. As the bulb increases, the flavor profile shift.
Sets are the little guys who grow up to be your own crop, also called planting stock, and they is covered in the visual guide. For gardeners, knowing how big they will get can help shape expectations. Each set begins as smaller than an inch, and may take several weeks to fatten up into something marketable. From there, it’s another couple months until harvest time. You see those tiny pencil-thin things grow up to make marble-size bumps and then gradually becomes the round balls we call onions (or at least ones headed that way). That’s how much work goes into that simple vegetable, and it’s not just any old commodity (it’s swollen-up storage biology).
So next time you’re standing in the grocery store, glance through the mesh bag. Note the diameter. Want to make a quick pickle? A robust goulash? Go for the small ones. Fancy some french onion soup? The bigger the bulb, the more sugar, so go for those. For a handy reference of what to expect when you go shopping, check out the table above, showing the maximum commercial diameter for each grade.
Don’t be fussy; be mindful that cooking is chemistry and size of an onion is something you can control. Start picking bulbs according to how they’ll fit into the dish, not just by the price per pound. You’ll taste the difference from there onward with every meal. The onion should became part of the dish, not overpower it, or fade into it. Get the size right and then get the flavor right.