Caramelized Onions

The science of caramelizing onions and an easy, fuss-free method for cooking your own caramelized onions

Science of Caramelizing Onions

I love a fun fact session on veggies especially since I'm shining a light on Veggies All Year. Today's topic is The Science of Caramelizing Onions.

So push those glasses back up your nose, pull out your periodic table, and let's nerd out with some food science today!

What is caramelization?

Caramelization is the process of browning that happens when sugar is heated. That's a very general statement, so let's get specific about caramelization of onions.

Caramelization of onions is the pyrolysis of sugar, which is a non-enzymatic browning reaction. What that means is that it's not a browning because the food enzymes react with oxygen (generally the air). Think about when you cut an apple and it turns brown shortly thereafter; that's enzymatic browning.

When you cut an onion it stays the same color and only changes color when heat is applied, so it's a non-enzymatic reaction.

Pyrolysis is a chemical change that is caused by the presence of heat. This is the reaction that takes place to cause the caramelization of onions. Pyrolysis involves a chemical and physical change; in the case of the onion

• the chemical structure of the onion is changed by breaking down the larger starch and sugar molecules in the onion
• the physical structure is changed from a yellow-white color to a caramel-brown color

Breakdown of the onions

From crispy & pungent, to soft & sweet...

First, the onions are sliced then added to a hot skillet. The heat causes the water in the onions to evaporate which is why they start "sweating."

Onions are about 89% water, so they have lots of sweating to do -- lots of water that will be released because they are being heated. The release of the water causes a breakdown in the structure of the onions, which is why they start softening. However, at this point, the onions are still heating up. They aren't hot enough yet to start the pyrolysis -- which happens above 212°F.

Once the onions have reached the temperature where pyrolysis starts to happen, they start their browning. And this is where the magic happens. It's also where you need to make sure not to let the onions burn. Basically, just stir them every 5-10 minutes. I find that I could go longer intervals in the beginning and then as it got closer to the end, I needed to keep a more watchful eye on my beloved caramelized treasures.

During the caramelization time, the larger sugar molecules in onions are broken down into smaller, simple sugar molecules. This is why caramelized onions have a sweeter taste than their raw counterparts. Your tastebuds don't register the large sugar molecules; they acknowledge the simple sugar molecules (not to be confused with "simple sugars" like table sugar).

How to Caramelize Onions

Now you know the science - how exactly do you do it?

It's easy, and this is my favorite no-fuss, minimal effort, works.every.time method.

A few things to know before you get started...

• 1 pound of onions is about 3-4 medium onions
• 1 pound of onions is about 4 cups sliced raw onions
• 1 pound of onions yields about 1 cup caramelized onions
• you'll use 1 tablespoon of fat -- either butter or oil -- per pound of onions

Start by thinly slicing your onions, trying to get them to be similar in size. Similar size means more even cooking. Uneven sizes means uneven cook time, so try to have a generally similar size for all your onions.

Then heat your skillet or dutch oven over medium heat. Add the fat - either butter or oil or a combination. For one pound of onions, I usually just use a tablespoon of butter. But if I am making a big batch, I'll do a mixture of butter and oil for a little extra flavor.

Once your butter or oil is hot (but not smoking), add the onions. Stir them around to coat them in the fat, and make sure they are spread in an even layer in the pan.

Let them cook about 5-10 minutes. Then stir. After about 15-20 minutes, your onions should start to be browning. At this point, I like to turn down the heat a little but it's optional.

Some people like to add salt and/or add a pinch of sugar. The salt will help the onions release more of their moisture, supposedly helping them to break down faster but I don't know that I've ever noticed much of a difference.

The pinch of sugar is supposed to help them develop even more of a caramelized flavor - don't know that this is a mandatory step either. I usually skip it because it means that I have to remember one more thing.

After they've cooked for 25 minutes, you'll need to pay a little more attention to the onions, stirring them every 5 minutes or so to keep them from browning. If they are sticking to the pan, then you can add a few tablespoons of water, broth, or wine to help release the brown bits from the bottom of the pan.

Once they've been cooking about 45-60 minutes, your onions should be caramelized to perfection. I think that it's a personal preference to how caramelized you want them, but be cautious that you don't burn them.

Some people like to add about 1/2 cup of water or a few tablespoons of balsamic vinegar at this point. It definitely adds depth of flavor but it is optional.

Once your onions are ready, either eat them immediately, or let cool and transfer to your fridge or freezer. Caramelized onions can be kept in the fridge about one week and in the freezer for a few months.

I recorded my 54 minute process of caramelizing the onions, so you could see what happens in about 50 seconds. Enjoy! P.S. click here if you can't see the video.

I highly suggest taking the time to make a big batch of caramelized onions to keep in your fridge.

They add so much flavor to everything - sandwiches, eggs, pasta, burgers, dips, the list goes on... It's a great thing to do over the weekend when you have a little extra time to spend in the kitchen.

Caramelized Onions Recipe

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