Crock-Pot Caramelized Onions — Slow and Steady Does the Trick

by Dorothy Reinhold on February 21, 2011

Print This Post Print This Post Caramelized Onions in the Crock-Pot on Shockingly Delicious

Shockingly Delicious Cooking Class

Caramelized onions are one of those cooking tricks that can make a side dish go from merely meh to marvelous.

Throw them in cheater mashed potatoes (instant potatoes, doctored up) and you won’t recognize the spuds came from a box. Stir them into sautéed green beans or wilted greens, sprinkle atop a pizza or use as a condiment on roast chicken or even a grilled steak. It all works, and their transformative power is surprising in the best way.

Caramelized onions are traditionally done stove-top, in a skillet over long, low heat, but the slow cooker, with its “throw it in and forget it” vibe, does a very nice job on them, too, with far less time needed to directly tend them.

And since time is money, this easy version wins on several counts. For our next Shockingly Delicious Cooking Class, let me teach you how to make caramelized onions in the slow cooker:

Onions on chopping board from

Peel and slice the onions in half.

Chopping onions from

A sharp knife is essential. Prepare to cry.

Sliced onions in a Crock-Pot from

Into the crock the onions go.

Onions in the Crock-Pot from

Be sure to remind yourself when they are expected to be done.

Caramelized onions from

Put them in small containers for freezing. These hold about 1/4 cup.

Caramelized onions in freezer bag from

Place containers in freezer bag and label. Always label!

Dorothy’s Crock-Pot Caramelized Onions

  • 6 large regular yellow onions (3-4 pounds)
  • 2-3 tablespoons good quality olive oil

Peel onions and cut them into thin slices; you should have about 6 cups (exact amount is not crucial, though). Mist the inside of the ceramic insert for the slow cooker, place onions in cooker and drizzle the oil over the slices. Cover and cook on high 10-12 hours, until the onions caramelize. They will have a deep brown color.

Leftover caramelized onions may be refrigerated, covered, up to a week or two. They may be frozen up to 6 months.

Makes 3 cups.


  • Portion out the caramelized onions into little freezable containers, label them and freeze for future use. I usually have 1 opened container in the refrigerator, and the onions find their way into many things as I’m cooking during the week. When I use those up, I can just reach for another small container from the freezer and I’m ready to go again.
  • You may use butter instead of olive oil. I skew to olive oil for health reasons, but butter is what you would use if you were doing them in a skillet.

Sweet vs. regular onions (also called storage onions)

You will get best results in this recipe by using regular onions, according to Kim Reddin, director of Public and Industry Relations for the National Onion Association.

She says: Sweet onions (examples: Vidalia, Texas 1015, Walla Walla, Imperial Sweets, Oso Sweet onions, Maui Sweets) are higher in water content than cooking/storage onions available this time of year from the U.S.  Most yellow storage onions are lower in water content and higher in sugar content.  This means two things:

  1. Because storage onions have a higher percentage of solids and less water (in comparison to sweet/mild onions), they are ideal for long cooking. Storage onions (available September-April) hold up better under long periods of heat and will produce a higher yield.
  2. When you eat raw storage onions, you will taste the sulfur compounds that give them that strong onion flavor; however, when you apply heat to them, the sulfur compounds dissipate, allowing the sugars to become caramelized.  Our palate doesn’t perceive the high sugar content until heat is applied.  When heat is applied to sweet/mild onions, often the sugars evaporate in the water shed during the heat process, leaving a “weak” onion flavor.

What is caramelization?

It refers to the burning or breaking down of any sugars in foods, according to food sleuth Shirley Corriher. In her book “CookWise,” she writes: “When onions cook, some of the their strong sulfur compounds dissolve and break down, and many evaporate. New compounds are formed. Some of the compounds that form in onions are even sweeter than sugars.”

Big bowl of caramelized onions from

{ 33 comments… read them below or add one }

Ginger September 9, 2012 at 9:15 am

I made these overnight and they turned out amazing! My small (1.5 qt. I think) Rival Crock Pot, about 6 years old so not ‘vintage,’ held three medium onions (regular yellow) and reduced down to about 3/4 cups very brown onions after about 10 hours total cooking. I used butter instead of oil and added salt just because I mindlessly add salt to everything, but it probably isn’t necessary with salted butter (or at all?). They may not be “proper” caramelized onions, but they are SO delicious. They taste like French Onion soup without the soup. I only ended up with a teaspoon or two of extra buttery liquid (which I saved for sauteeing), but I think what helped is that after about 3.5 hours I checked and they were quite watery, so I cracked the lid for a couple of hours, then finished for another few hours with the lid back on. I’ve got another batch going now!


Dorothy September 9, 2012 at 9:26 am

Fabulous! Thanks for all the details in how it worked for you. I’m sure that will help someone else in the future.


Jeremy July 9, 2012 at 10:33 am

I tried this recipe out, and I wound up with blackened-ash onions! I’m just curious, do you know what temperature your crock pot “high” setting is at? My “high” setting, is at 212 Fahrenheit. Thanks, can’t wait to give it another go, maybe at a lower temperature!


Dorothy July 9, 2012 at 4:42 pm

Oh no! I’m sorry to hear that. I haven’t had any other reports of onion ash. I don’t know what temp my high setting is. I usually use the old 1970s Crock-Pot for the onions, because I like it better than my newer version. I have heard people say that the new C-Pots heat at a higher temp than the vintage versions, but I dunno. Perhaps if you are willing to try them again, do it on the low setting. (Luckily, onions are affordable, so it isn’t like burning lobster or something.) Maybe your low = my high. I do know that all slow cookers are different, by brand (Crock-Pot being Rival’s brand name) and year and model. Sigh. Let me know how it goes for you, and thank you for your feedback.


Jeremy July 9, 2012 at 6:18 pm

My crock-pot is brand new, so the temperature difference is probably the issue. I’ll try it on low and let you know how it turns out!


Dorothy July 10, 2012 at 12:23 pm

Great! I am really interested in your results.


oldmoose May 2, 2012 at 9:54 am

will this recipe work if I use a crock-pot liner from Reynolds?


Dorothy May 2, 2012 at 10:59 am

I have not tried it, but I don’t see why it wouldn’t work. If you try it, please come back and let me know your results!


Erik May 2, 2012 at 9:05 am

the directions say cook for 10-12 hours, but in the picture it indicates they’ll be done in 8-10 hours… is either one okay?


Dorothy May 2, 2012 at 11:07 am

I am chuckling at how observant you are! The short answer is yes. The longer answer is that all Crock-Pots cook at different heats (especially older versions such as I was using here), and so there can be a range of times. In the photo that shows the note I left myself, I was telling myself to check it between 8 and 10 hours. At 8 hours, I thought it needed more time, so I called for 10-12 hours in the recipe. But yes, anywhere in that range of time should work. You will pull some out and taste them, and if you think you would like to see them darker, or softer, leave them in another hour or two, and taste again. Hope that helps!


PaisleyGrace April 16, 2012 at 9:37 pm

I’m making these tonight for fajita’s tomorrow. I cannot wait!

Reply March 6, 2012 at 2:59 pm

Best cry I have had in a long time! Cooking these now and I can’t wait!


John February 27, 2012 at 10:18 am

Using a crock pot seems to only slowly brown the onions, not caramelise them in the true sense of the word (at least that was my experience when I tried this). Most crock pots would reach a maximum temperature of around 93 degrees C, which is a lot lower than the minimum caramelising temperature of fructose (110 degrees) (which has the lowest minimum caramelizing temperature of a group of sugars including Galactose,surose,glucose and maltose). The observed browning in the crock pot is more likely to be from maillard reactions, which are a distinct process.
Try it by all means, but it only browns the onions, don’t expect onions fit for a good onion soup with this method.


Dorothy February 27, 2012 at 10:48 am

Thanks for the explanation. Yep, these are not entirely traditional caramelized onions.


Sarah L September 13, 2013 at 4:17 pm

This is not entirely correct. From Suzanne Driessen, University of Minnesota Extension Regional Extension Educator: “Most slow cookers have two settings low and high. The low setting cooks at around 200F (94c) and the high setting at about 300F (149c).”

The exact temperatures vary by model, but a high setting is well within the range of temperatures that will caramelize.


Tracie October 8, 2011 at 5:49 pm

Fantastic how-to on crockpot onions. My brother is a long distance truck hauler and from time to time, he hauls onions and they always end up giving him HUGE bagfulls of them that he puts in his garage and lets family and friends come and take as many as they want. I just picked up some this past week and I am the proud owner of some giant giant yellow onions, not just some, but dozens upon dozens. Am going to start caramelizing some this evening, thank you for this blog post!


Dorothy October 9, 2011 at 4:56 am

I am picturing a pile of onions in a garage, and getting jealous! Let me know how yours turn out.


jan March 17, 2011 at 7:41 pm

I have made this recipe twice and will always use it from now on. With that being said, too much water remains after the 12 hours in the crock pot so I put them in my skillet and finished carmelizing them in that. Yummy..jan


Dorothy March 17, 2011 at 8:13 pm

Sorry you had watery onions! I haven’t encountered that problem, but I do think onions differ in water content. So glad you like them, and yes, you’re right, a quick finish in the skillet should take care of it. Well done!


Sylvia March 13, 2011 at 5:34 pm

Dang! I don’t even know where my crock pot is. This recipe is a good reason to buy a new one. I can’t wait to try it. Sounds so good.


Dorothy March 13, 2011 at 5:51 pm

The Crock-Pot is one of my favorite things! I would search for it, if I were you!


Deb March 10, 2011 at 4:18 pm

I think I will try french onion soup


Wendy March 1, 2011 at 8:22 pm

That is AWESOME! Thanks for sharing at Tip Day Thursday last week. I can’t wait to give these a try. I love that you can freeze them too….

I am highlighting your blog and this post in the upcoming TDT. Feel free to stop by my site and grab the “featured on” button if you’d like. Please link up again soon!

Around My Family Table


sippitysup February 23, 2011 at 7:23 pm

You are weakening my resolve against crockpots. I love caramelized onions but hate standing there stirring away the pan half the day. GREG


Nancy@acommunaltable February 22, 2011 at 10:32 pm

These are “da bomb”!!! I just so happen to have a batch of these in my refrigerator as we speak!! Amazing return for the time investment !!!


Lamb February 22, 2011 at 7:57 pm

Thanks for posting Caramelization 101. I’ve never quite gotten the hang of it and always end up with onions that are either over or underdone.

I’m stopping by tonight to let you know that there is a fun surprise waiting for you on my blog! And to wish you good luck 🙂


Dorothy February 23, 2011 at 10:30 am

Thanks Lamb!
Everyone, Lambaround has nominated my blog for a “Best in Show” this week, so please go here and vote for Shockinglydelicious! Thank you!


Kate February 22, 2011 at 1:46 pm

I adore my crock pot and I cannot wait to give this a go – thank you for this recipe.


Dorothy February 23, 2011 at 10:32 am

Kate, you are welcome!


Ann Walker February 22, 2011 at 8:29 am

WOW! I can’t wait to try this!


Sheila Denise February 21, 2011 at 5:28 pm

This has inspired me. I see a goat cheese and caramelized onion pizza in my future.


Dorothy February 21, 2011 at 6:38 pm

Love that idea! Try it also with a pinch of very finely minced fresh rosemary!


Dorothy May 2, 2011 at 4:24 pm

So glad to see you are trying these this week! Hope you like them!


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