Modernist onion soup

Although beans were one ingredient I was looking forward to making in my new pressure cooker, they weren’t the main reason I decided to buy one: having recently acquired my copy of Modernist Cuisine, I knew there were going to be a bunch of preparations I would want to try that needed to be cooked at high pressure.

Many chemical reactions speed up as you raise the temperature. For example, when you mix baking powder into a room-temperature batter, you might get a slight fizz, but once you put that batter in the oven, the bubbling increases dramatically, and produces the lift that makes your muffins light and airy. So it goes with many culinary preparations, such as the browning reactions, both caramelization and Maillard reactions, involved in making French onion soup.

Traditionally for onion soup, you cook the onions slowly and gently to make sure they don’t burn. For Modernist Cuisine onion soup, you throw all the ingredients into jars, put the jars into a pressure cooker, bring it up to high pressure, and hold it there for 40 minutes. (If you happen to have an autoclave handy, it takes only 20 minutes.) Because the Maillard reactions are involved, and because their rate is limited by acidic environments, the ingredient list includes a small amount of baking soda to speed them up. Of course, I’ve been browning onions with baking soda for a while, ever since reading about it on Khymos.

As I was packing the sliced sweet onions into the jars, I wasn’t quite sure they were all going to fit, but they did. Barely. A few peppercorns, some butter, sugar, ruby port, thyme, onion juice, made in my handy juicer, and the aforementioned baking soda filled in the gaps. After nervously pacing for 40 minutes – hey, I’m still getting used to cooking in a pressure cooker! – I let the pressure come down, and removed the jars, whose contents had gone from bright white to a rich brown.

The resulting soup, seasoned with salt and sherry vinegar, was good, with satisfying meaty flavours from the browning reactions, and a little richness from the butter. The original recipe calls for a cheese foam to layered on the surface, but I’m missing some of the stabilizers in the recipe, so I omitted it. I also omitted the more traditional cheese croutons – a mistake that I won’t make again. If I had one complaint about the soup, it would be that it was slightly too sweet. This could be easily corrected by using a heavier hand with the sherry vinegar, but I’d also be curious to see what it the results of using a mix of sweet onions and regular cooking onions.

In any case, I will happily make this soup again. The bonus is that the leftovers are already nicely packaged in a jar to go in the fridge!

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