Can caramelised onions be stored?

Caramelised onions are a versatile ingredient that can add depth of flavor to many savory dishes. Their sweet, jammy texture makes them an ideal topping for burgers, sandwiches, pizzas and more. However, properly storing leftover caramelised onions is key to maintaining their quality and flavor over time.

Can you freeze caramelised onions?

Yes, caramelised onions can be frozen for long-term storage. Freezing is an excellent way to keep caramelised onions fresh for up to 3 months. To freeze caramelised onions:

  • Allow cooked onions to cool completely before freezing.
  • Portion onions into freezer-safe bags, containers or ice cube trays.
  • Remove as much air from the bags or containers as possible.
  • Label bags or containers with contents and date.
  • Freeze for up to 3 months.

When ready to use, thaw frozen onions overnight in the refrigerator or for a few minutes in the microwave. Use immediately after thawing.

How long do caramelised onions last in the fridge?

Properly stored, caramelised onions will last 3-4 days in the refrigerator. To maximize refrigerator shelf life:

  • Allow onions to cool to room temperature before refrigerating.
  • Transfer to an airtight container.
  • Press plastic wrap directly onto the surface of the onions.
  • Refrigerate for 3-4 days.

Check refrigerated onions daily and use immediately if any mold appears or if the onions take on an unpleasant odor.

What’s the best way to store caramelised onions?

For short-term storage, the refrigerator is best. Freeze caramelised onions for longer term storage. Here are some storage tips:

Refrigerator Storage

  • Let onions cool completely first.
  • Store in an airtight container like a mason jar or plastic container.
  • Press plastic wrap directly on the surface before sealing the container.
  • Use within 3-4 days.

Freezer Storage

  • Portion into freezer bags, containers or ice cube trays.
  • Remove as much air as possible before sealing.
  • Label with contents and freeze date.
  • Freeze for up to 3 months.
  • Thaw refrigerator overnight before using.

What container is best for storing caramelised onions?

The best containers for storing caramelized onions include:

  • Glass jars – Mason jars or other glass food storage jars are ideal. The airtight seal prevents air exposure.
  • Plastic containers – Look for BPA-free plastic containers with tight-fitting lids.
  • Vacuum seal bags – Vacuum seal bags remove air and keep onions fresh for freezer storage.
  • Aluminum foil – Onions can be placed in aluminum foil pouches for the freezer.
  • Ice cube trays – For portioning onions into ready-to-use cubes.

Avoid non-airtight containers like bowls covered in plastic wrap. Air exposure causes onions to spoil faster.

Do caramelised onions need to be refrigerated?

Yes, it is important to refrigerate leftover caramelised onions. At room temperature, the moisture content of the onions creates an environment susceptible to rapid bacteria growth. Refrigeration is necessary for safety and optimal shelf life.

Refrigerate caramelised onions within 2 hours of cooking. Let them cool to room temperature first, then transfer to an airtight container. Place in the refrigerator immediately and use within 3-4 days for best quality.

Can you get sick from eating bad caramelised onions?

Yes, consuming spoiled, rotten or moldy caramelised onions can make you sick. The bacteria that cause onion spoilage can lead to foodborne illness if ingested. Potential symptoms include:

  • Nausea
  • Vomiting
  • Diarrhea
  • Abdominal cramping
  • Fever

Discard caramelised onions immediately if they develop a slimy texture, smell unpleasant or have visible mold. Only keep refrigerated onions for 3-4 days maximum, even if they look fine. When in doubt, throw them out.

How can you tell if caramelised onions are bad?

Look for these signs that indicate caramelised onions have spoiled:

  • Slimy texture – Onions turn slimy as bacteria multiply.
  • Mold – Fuzzy mold growing on the onions signals spoilage.
  • Unpleasant sour smell – Onions give off a rancid, vinegary odor.
  • Dark spotting – Black or brown splotches appear on the onions.
  • Soft texture – Onions look or feel overly soft or mushy.

Trust your senses – if caramelised onions look, smell or taste off, err on the side of caution and throw them away.

What are some uses for leftover caramelised onions?

Don’t let leftover caramelised onions go to waste! Here are some delicious ways to use them up:

  • Mix into dips, spreads and sauces for a sweet flavor
  • Top sandwiches, burgers, hot dogs or pizza
  • Stir into omelets, frittatas or scrambled eggs
  • Toss with roasted vegetables
  • Blend into soups, stews or chilis
  • Fold into rice or grain dishes
  • Serve over roasted meats
  • Add to pasta dishes like mac and cheese
  • Saute into hash or breakfast potatoes

With their jam-like texture, caramelised onions pair well with both savory and sweet foods. Get creative with leftovers in quiches, flatbreads, salads, dips and more.

What’s the best onion for caramelising?

The best onions to use for caramelising include:

  • Yellow onions – An all-purpose onion that caramelises well. Sweet with a mild flavor.
  • White onions – Very mild tasting and turn a light golden brown.
  • Shallots – More subtle and sweet than other onions.
  • Sweet onions – Vidalia, Maui, Walla Walla. Very sweet and take longer to caramelise.

Avoid red onions – they turn an unappealing grayish color when caramelised. Don’t use green onions either, as they contain too much moisture.

Do you need oil to caramelise onions?

Yes, you need some type of fat or oil to properly caramelise onions. Oil helps facilitate the maillard reaction – the chemical process that causes browning and flavor development.

Good options for caramelising onions include:

  • Olive oil
  • Butter
  • Bacon fat
  • Coconut oil
  • Lard
  • Tallow

Use just enough oil to coat the bottom of the pan, about 1-2 tablespoons. Too much oil can prevent browning. Stir onions frequently so they cook evenly.

What’s the difference between caramelized and brown onions?

Caramelized onions and brown onions may look similar, but differences in cooking method and flavor set them apart:

Caramelized onions Brown onions
Cooked slowly over low heat Cooked over high heat
Takes 30-60 minutes Take 10-15 minutes
Jammy, sweet flavor More crisp, bitter flavor
Translucent to deep brown Light to dark brown outer layer

The long, slow caramelization process causes onions to turn an amber color and develop rich, nuanced sweetness. Browning happens faster, giving onions just a hint of bitter flavor.

How long does it take to caramelise onions?

Caramelizing onions properly takes patience – anywhere from 30-60 minutes depending on the amount and type of onions. Here are some general timelines:

  • 1 large onion: 30-40 minutes
  • 1-2 pounds onions: 45-60 minutes
  • Sweet onions: 45-60 minutes (take longer)

The process consists of:

  1. 10-15 minutes sweating on medium-low heat
  2. 15-30 minutes slowly browning on low heat
  3. 5-10 minutes deglazing pan to deepen color

Rushing the caramelization process by using high heat will make onions bitter and unevenly cooked. Be patient and let them develop flavor slowly for best results.

What’s the best way to chop onions for caramelising?

The way you chop onions for caramelising affects how quickly they cook and brown. Some guidelines include:

  • Smaller pieces = faster cooking time
  • Thin slices = more surface area to brown
  • Consistent sizing = even cooking

The most common methods are:

  • Thin slices – 1/4 inch slices caramelise quickly.
  • thick slices – 1/2 inch slices maintain structure longer.
  • Half moons – horizontal half circles, good for sandwiches.
  • Dice – 1/4 to 1/2 inch dice work well.

A food processor can make quick work of slicing or chopping. Hand cut for the most even, consistent pieces.

What temperature do you caramelise onions?

The ideal temperature for caramelizing onions is between 225-300°F. This low and slow cooking allows the natural sugars in the onions to break down and develop complex flavors.

Start by cooking over medium-low heat for 10-15 minutes to sweat onions. Then reduce heat to low and cook for 15-30 minutes more until deep brown. Stir frequently and regulate heat to maintain 225-300°F.

If the pan gets too hot, onions will burn. Too low, and onions won’t brown properly. Use a digital thermometer to monitor temperature for best results.

Can you speed up caramelising onions?

While the long cook time required can’t be avoided, a few tips can help speed up caramelizing onions slightly:

  • Slice thinly – More surface area browns faster.
  • Cut consistently – Uniform pieces cook evenly.
  • Use a wide pan – More onion contact with pan.
  • Stir frequently – Prevents burning and hot spots.
  • Deglaze pan – Helps release sugars and deepen color.

Avoid rushing the process too much. Lower heat and take your time for the best flavor development. A little patience yields sweet, caramelized onions!

Can you cook caramelised onions in the oven?

Yes, you can absolutely caramelise onions in the oven! The low, even heat of the oven is well-suited for slowly cooking down onions.

To caramelise onions in the oven:

  1. Slice onions about 1/4 inch thick.
  2. Toss onions with 1-2 Tbsp oil on a rimmed baking sheet.
  3. Roast at 225°F for 45-60 minutes, stirring occasionally.
  4. Once deep brown, remove from oven and let cool before storing.

The gentle heat prevents scorching and allows onions time to fully caramelize. Feel free to toss in some fresh thyme or rosemary before roasting too!

Can you use a slow cooker to caramelise onions?

A slow cooker isn’t the ideal appliance for caramelising onions. It can be done, but a few modifications are needed:

  • Use only 1-2 pounds onions max.
  • Slice onions thinly, about 1/4 inch.
  • Cook on LOW up to 8 hours.
  • Prop lid open with a chopstick to allow moisture to escape.
  • Stir onions every few hours as needed.

The downside is onions come out very soft and less browned than oven or stovetop methods. For best results, cook onions low and slow in a pan on the stovetop or roast in the oven.

Can you use any type of onion to caramelise?

You can caramelize any type of onion, but some work better than others. The best onions to caramelise include:

  • Yellow
  • White
  • Sweet (Vidalia, Walla Walla, Maui)
  • Shallots

Avoid red onions – they tend to turn gray and mushy when caramelized. Green onions are also too watery.

When choosing onions, look for ones with higher sugar content and lower moisture for the best caramelized flavor.

Is there a shortcut for caramelising onions?

Unfortunately, there is no real shortcut for properly caramelising onions. The process relies on slowly cooking down onions to draw out their natural sugars and develop complex flavors.

However, you can prep onions in advance to make the process a little faster:

  • Chop all onions ahead of time so they are ready to cook.
  • Consider doing a big batch and freezing extra caramelised onions.
  • Microwave onions for 5-10 minutes first to release moisture.
  • Use a mandoline for perfectly thin, even slices.

But keep in mind – rushing the cooking process too much can make onions bitter. Be patient and keep heat low and slow for the best results.


With their concentrated flavor and silky texture, caramelized onions are worth the time investment. Proper refrigeration and freezing allows you to enjoy their sweet jammy goodness long after cooking. Follow these storage guidelines and tips for caramelising, and you’ll be able to keep a stash of onions on hand anytime.

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