Peeling back the layers

rich in sulphur, which it absorbs and transforms into defensive compounds stored in its cells. These cells rupture as we chop, or as pests chomp, and an enzyme in the plant combines with the sulphur compounds to produce an irritating, pungent group of molecules called thiosulfinates and thiosulfonates.

Sweet onions are grown in sulphur-poor soil and are less likely to make one cry. But they have a higher water content (as much as 95%), giving them a much shorter shelflife of just one month, without refrigeration.

Now for some not-so-great news. Each bulb is rich in flavour, even though it’s about 80% water. But that flavour comes largely from sugars. The average onion (110 gm) contains 45 calories and only 1.9 gm of dietary fiber and 1 gm of protein, compared with, for instance, green peas, which contain 5 gm of fiber and 5 gm of protein per 100 gm.

Onions are a good source of antioxidants, though, with the greatest concentration in the layers near the peel. One bulb also contains 20% of a person’s daily requirement of Vitamin C. This, combined with its long shelf-life, made it very popular among sailors, as a way to prevent scurvy on long voyages in the 1800s.

It is, of course, a supremely versatile vegetable. A cook who knows how to manipulate the sulphur and sugars can elicit a wide variety of flavours from the same bulb. For starters, before cutting it, it helps to chill the onion briefly; the cold deactivates some of the enzymes, leading to less tears.

Next, how you chop it matters. Because the cell walls line up from root to the tip, cutting lengthwise rather than widthwise releases fewer sulphur molecules. Finely chopping or pureeing it, on the other hand, releases a lot of sulphur compounds. However, if you can withstand the tears, you will be rewarded. When heated, these sulphur molecules break down to provide a rich, savoury flavour to a dish.

To get the raw crunch without the pungency, it helps to soak the chopped bulb in water for about 30 minutes. This allows most of the sulphur compounds formed on the cut surfaces to wash off, softening the sharpness.

Let’s say you only want sweetness from the onion. It helps to remember that the sugars are hidden behind the pungency of the sulphur molecules. To tease them out, be patient and slow-cook. The sulphur compounds will break down first. Then, with slow, gentle heat, the sugars break down and, combined with the protein, brown the whole, creating the subtle, sweet flavour of caramelised onion!

It’s just layers and layers of possibility.

(To reach Swetha Sivakumar with questions or feedback, email upgrademyfood@gmail.com)