Why It's So Much Easier to Caramelize Onions in a Rice Cooker
Caramelizing onions is probably the most frustrating technique for many home cooks (and restaurant cooks, for that matter). It is a long, delicate operation with plenty of opportunities for disaster. If there is too much heat, the onions will burn long before they have caramelized. If the onions dry out too much, they will burn. If there are pieces that are too thin, they will burn. If there is too much fat, they will burn. If you look at them the wrong way... You get the picture.
Although we usually don't think of them this way, onions are root vegetables, meaning that their purpose is to store sugar, in the form of fructose, that the plant will need later. Fructose caramelizes at the lowest temperature of all sugars, nearly 100 degrees (F) below where sucrose (table sugar) and proteins caramelize. Since caramelizing foods is the process of heating them to their browning point, their blackening point is never far off. The very low temperature at which fructose browns is so far below all of our normal cooking processes, that charging past it is ridiculously easy, and burning happens frequently.
The biggest challenge with caramelizing onions in a pan on the stove top lies in controlling heat and evaporation. An electric heating element or a gas flame will continue to provide heat to the pan regardless of what is going on inside it. The same for the pan. It will continue to transfer heat to it's contents at a steadily (even if slowly) increasing level. An uncovered, wide bottomed saute pan encourages evaporation by providing a large surface area where steam can escape. Escaping steam is what allows temperatures to increase to a food's browning point, and also what causes foods to sear and burn. If the pan is covered, the water vapor condenses on the underside of the lid and falls back onto the pan's contents, making it difficult for the temperature to rise above water's boiling point, which is too low for caramelizing foods. It steams them instead.
To caramelize onions on the stove top, all of these factors must be managed in a careful balancing act that lasts for about an hour, or even more. Not to mention the effects that humidity and ambient room temperature will have on the process. And the closer you are to being finished, the more chances there are for the whole thing to go south, meaning that 45 minutes in, you're throwing everything out and starting all over again. It's no wonder that this process thwarts even the most experienced cooks.
So, what is it about a modern Japanese appliance that makes a classic French technique so much easier? The answer lies in temperature control and evaporation control.
A rice cooker is designed to apply heat based on the temperature of its contents. If the food in the inner cooking bowl reaches a temperature of around 225 - 240 degrees (F), the unit will cut back the heat to it's lowest setting (Keep Warm). This is because the machine was engineered to judge that rice is fully cooked when all of the boiling water – which has kept the internal temperature at a steady 212 degrees (F) – has been absorbed, allowing the temperature of the contents to rise above the trigger amount.
The lid of the rice cooker contains a vent that was designed to allow water and rice to boil with just enough steam escaping so the pot doesn't boil over (usually) and the lid doesn't blow off from a build up of pressure. This steam vent allows evaporation to occur at a controlled pace. Evaporation control helps keep temperatures steady by keeping enough moisture present so that food in the rice cooker doesn't bolt past the machine's shut off trigger of 225 – 240 degrees (F).
The Role of Fructose:
The caramelizing point of fructose (which is the sugar in onions) is a nice, convenient 230 degrees (F). This means that, once enough of the water has evaporated for the sugars in your onions to begin browning, the rice cooker will switch off before the temperature gets high enough to burn them. As a side benefit, this also provides a reminder that onions must be stirred every few minutes throughout the caramelizing process.
Caramelizing onions in the rice cooker doesn't take longer than on the stove top. Both techniques will take between 45 and 90 minutes. The thickness of the onions, their water content, the humidity and temperature in the room, your elevation and the phase of the moon (not really, but sometimes it feels that way) will all affect the final cooking time. There is no easy way to determine how long it will take until after you're done. Plan on at least an hour of cooking time.
Here are some tips to keep in mind:
Onions can be sliced or diced, depending on the recipe or how you plan to use the finished product.
Diced onions are great in dips and jams, or appetizers.
Sliced onions work well in sandwiches and soups.
Slices or dices should be of a uniform size so that all pieces cook evenly. When peeling, be sure to discard the papery skin and any thin, dry outer layers of the onion to help prevent burning.
Separate all of the layers of the onion after cutting, again, uniform thickness helps with even cooking.
Use a neutral cooking oil like canola, grape seed or peanut oil, as the long cooking time can sometimes give fruitier oils (live olive oil) a bitter flavor.
Don't use whole butter, for the same reason as not using fruity oils. Clarified butter (ghee), which has had all of the milk solids removed, will work just fine, however.
Thoroughly, but gently, toss together the onion and oil. The goal is to evenly coat all of the onion pieces in some of the oil. Your hands are a great tool for this process.
Salt lightly. Salt will draw moisture from the onions, and too much will dry them out too quickly. Plus, caramelized onions are often used as a component in other recipes, and the salt level of the onions will impact your final dish.
Stir, stir, stir. This is not a push Cook and walk away dish. The onions need to be stirred every two to three minutes to prevent the ones on the bottom from burning.
You may not be finished when the rice cooker switches to Keep Warm! The first time this happens, you may still have sauted onions, not caramelized ones. Stir the onions, cover and push Cook again. Repeat stirring and pushing Cook as many as 10 or more times for deeply caramelized onions. They are done when they taste the way you like them.
Perfect Caramelized Onions recipe