A building block to good flavor and the foundation of many stews and sauces involves caramelizing onions. Think French Onion Soup. It’s not difficult to do, but it does require a bit of patience as it takes at least an hour depending on the number of onions you’re doing.
I don’t know about you, but I don’t have an hour to sit around and stir onions on a busy weeknight. That’s why I like to buy a big bag of onions when they’re on sale, and spend a few hours on a lazy Sunday caramelizing the whole bag. You can then portion the caramelized onions into ice cube trays and freeze them, allowing you to add a ton of flavor to a quick weeknight pasta sauce or curry.
Caramelizing onions is a three step process. During the first stage (45-60 minutes), you cook the onions with a lid, braising them in their own juices. The salt helps the onions release their liquid quickly so they don’t burn. You want to braise them in their own liquids until the onions are mostly broken down into a light brown mash.
The second stage (45-60 minutes), involves boiling off the liquid that the onions have released. During the final stage (about 30 minutes), most of the moisture has been driven off and you’re frying the onions in the oil that was added initially. This is where most of the caramelization happens.
Here are a few key points to speed things up and make the process easier:
- Slice the onions thin – The thinner you slice the onions the faster they will release water which means the sooner they will caramelize. You also want even slices, otherwise the onions will caramelize unevenly. A mandolin slicer is a fast way of getting thin even slices.
- Slice the onions in rings– By slicing the onions against the grain, they breakdown easier, speeding up caramelization. The finished caramelized onions will also melt into whatever you are making faster than if you cut them with the grain.
- Use a heavy bottomed pot – An enamel coated cast iron pot such as a Le Creuset or Staub is ideal because it will evenly distribute the heat. Thinner pans with hotspots will burn easier so you will need to be more diligent about stirring. This will become tiresome after 2 hours.
There are other shortcuts you can take, like raising the temperature, but this typically delivers unevenly caramelized onions, as the exterior of each onion slice will start burning before the interior is fully caramelized. You can also dramatically speed up caramelization by raising the pH of the onions (i.e. adding baking soda), however I’ve noticed this adds a slightly bitter metallic taste which is why I like to do it the old-school way unless I’m really pressed for time.
📖 Recipe
Units
Ingredients
- ¼ cup vegetable oil
- 16 onions medium (peeled with just the tops trimmed off)
- 1 teaspoon salt
Instructions
- Add the oil to a large heavy bottomed pot, holding the root part of the onion use a mandolin to slice the onions straight into the pot, discarding the root. When you're done slicing, add the salt and stir.
- Cover the pot with a lid, and then turn the burner on to medium-low heat. Cook covered until the onions have mostly broken down and are a pale brown sludge (about 45-60 minutes). Be sure to stir the pot periodically, checking to make sure the onions aren't burning. If they are, turn down the heat and add a bit of water.
- Once the onions have gotten to this stage, remove the lid and continue cooking until there isn't water vapor coming up from the onions (another 45-60 minutes). You'll want to stir the onions every few minutes to make sure they're not burning.
- Once most of the moisture has burned off, you'll need to constantly stir the onions, scraping up the bottom of the pot with a silicone spatula to keep the onions from burning. Fry the onions until they are very glossy and are the color of coffee with milk.
- If the onions start burning to the bottom of the pan before they reach this stage, deglaze the pan with a bit of water, scraping the browned bits off the bottom of the pot.
- Once your onions are fully caramelized, turn off the heat and allow them to cool. To store them for later use, fill a clean ice cube tray and freeze them. Once the onions are frozen you can remove them from the tray and place them in a Ziploc bag.
Marc Matsumoto says
Hi Bryan, it really depends on your freezer. If you have a deep-freezer they should last a very long time if packaged properly. If you're using a regular home freezer, they'll get freezer burn after a few months due to the deicing cycle of the freezer.
Bryan Leo Low says
Hi, how long can they be kept for after thier frozen?
Marc Matsumoto says
You an use regular vegetable oil, olive oil will work as well, but it will make your onions taste like olive oil, which is fine for some dishes, but can limit the places you can use the onions.
Hannah says
Is it important to use grape seed oil over vegetable or olive?
addison says
Thanks for the idea to freeze in ice cube trays. I also make large batches of carmelized onions but late at night while watching movies on TV 🙂
Marc Matsumoto says
Hi Steve, I like the way you think. I had the same idea a while ago and tried it but it doesn't work. The biggest issue is that the the pureed onions starts to burn and stick to the pan before the mixture is caramelized. This could be controlled by using a very low heat, but it will end up taking longer than just using thinly sliced onions. If you want to speed up the process, you can add a little baking soda to the mixture, which will speed up caramelization significantly, but will add a slightly off taste.
Steve moorens says
Could you use a food blender to make some sort of puree of the onions? All the liquids will be released already and maybe caramelization wll happen faster?
Oliver St.John-Mollusc says
hoh
Marc Matsumoto says
Hi Elle, I've switched to using mass based measurements for non-liquids, but unfortunately most of my past posts have yet to be updated. The good news is that for this particular recipe, precision is not important at all. Basically you you want to fill a 5-6 quart pot with sliced onions.
Elle says
Great idea. What would be much more helpful than the vague description "medium onions" would be weight or cups of onions. Thanks!
Marc Matsumoto says
Hahahaha, for me it has less to do with being organized and more to do with being lazy:-) Most of the time I can't be bothered to fully caramelize onions for everything I make, so this is just the perfect way to be lazy but get food that tastes laborious:-)
Jackie says
Well, this just blew my mind. Thanks Marc! I really must start being more organised...
Jax x
PS: I don't know if I told you how much I love the new design?
PPS: We are well overdue to meet somewhere in the world. Let's plan!
Marc Matsumoto says
Hahah great point! I bet she got quite a shock! Although caramelized onions are pretty sweet, they're probably the furthest thing from chocolate chip cookies that were in your freezer:-)
Judy says
Hmmm, this is a REALLY great idea! I tend to use a lot of onions, but never thought to caramelize them like this. I can see the convenience of having these in your freezer.I think I've found a use for my daughter's baby cubes (little individual size containers I used to freeze homemade baby food in) that we've since outgrown.
Jfood104 says
I love your blog. Starting reading it a few months ago and am hooked. I agree with a lazy sunday and 4 hours with 10 pounds of onions is well worth the investment.
Since I love them on hamburgers I freeze little circles on a tray and then wrap and freeze them. Then when I grill some burgers i have a great topping for them.
But please tell the family that they are NOT chocolate chip cookies since they have the same appearance when frozen in the freezer bag. Got a nasty call from my wife who thought she would have a treat when I was on a business trip and she had a sweet tooth.
Nathan Oberle says
I make a lot of strange caramel syrups that involve increasing the pH to get more or faster Maillard reactions. Bicarbonates are a weak base, so you need to use a lot to raise the pH. If you have a stronger base like pickling lime, you could use a much smaller amount, and the off-flavors from the base would probably be below the taste threshold. Baking soda and chalk tend to have a lower off-taste threshold in general. I've used potassium bicrabonate with fewer off-flavors than CaCO3 or NaHCO3, but pickling lime or caustic potash is best. (Potash is a PITA to handle though, so I'd stick with lime).
Nathan Oberle says
I make a lot of strange caramel syrups that involve increasing the pH to get more or faster Maillard reactions. Bicarbonates are a weak base, so you need to use a lot to raise the pH. If you have a stronger base like pickling lime, you could use a much smaller amount, and the off-flavors from the base would probably be below the taste threshold. Baking soda and chalk tend to have a lower off-taste threshold in general. I've used potassium bicrabonate with fewer off-flavors than CaCO3 or NaHCO3, but pickling lime or caustic potash is best. (Potash is a PITA to handle though, so I'd stick with lime).
Beckerniki says
just made these- it was reassuring to see these deep brown frozen wedges so i knew what i was going for- they're magnificent
Beckerniki says
just made these- it was reassuring to see these deep brown frozen wedges so i knew what i was going for- they're magnificent
Claudia says
When I first made French Onion soup, I followed the directions to cook the onions slowly, a bit fanatically. It said they were to be a deep medium brown and mine went 9 hours getting there. Lovely, though we had the soup next day.
Claudia says
When I first made French Onion soup, I followed the directions to cook the onions slowly, a bit fanatically. It said they were to be a deep medium brown and mine went 9 hours getting there. Lovely, though we had the soup next day.
IGredux says
you just changed my food world life... again. what a priceless technique. thank you very very much, marc. 🙂
Angela Roberts says
I have never thought of freezing onions. What a great idea for that flavor boost. Usually, which I think of caramelized onions, I never go this far in the process, but maybe I've been missing something.
Angela Roberts says
I have never thought of freezing onions. What a great idea for that flavor boost. Usually, which I think of caramelized onions, I never go this far in the process, but maybe I've been missing something.
nokomarie says
It's worth considering, I'm usually not looking for the sludge stage but this is the sort of restaurant technique at home trick that can be quite useful. The introdutory paragraphs made me laugh out loud however, another task for the mythic "lasy Sunday at home list" one should really do sometime or other.
Marc Matsumoto says
The onions not turning into a sludge is fine, you've probably just been cutting the onions with the grain. I just like cutting them against the grain and letting them melt because they tend to caramelize more evenly that way, and the resulting onions incorporates more smoothly into whatever I add them to.
Brian @ A Thought For Food says
2 hours!?! Amazing! I bet these really are perfect. Thanks for sharing your technique!
Ari says
I've never had caramelized onions turn into a sludge like that before. o.o I must be doing it wrong. Normally they just turn golden brown but they keep their onion slice shape. I guess that means I've never had caramelized onions. xD I'm gonna have to correct this.
Brian @ A Thought For Food says
2 hours!?! Amazing! I bet these really are perfect. Thanks for sharing your technique!