Caramelized Onion Relish with Balsamic Recipe

Caramelized onion relish with balsamic is a simple yet flavorful condiment that elevates everyday dishes. By slow-cooking onions, their natural sugars caramelize, creating a sweet, rich base. Balsamic vinegar adds a tangy depth, while olive oil, salt, and pepper enhance the overall taste. This relish complements sandwiches, burgers, meats, cheeses, and vegetables, making it a versatile addition to your kitchen.

Key Points:

• Ingredients: Onions, balsamic vinegar, olive oil, sugar, salt, and pepper.
• Cooking Process: Slow caramelization of onions, followed by deglazing with balsamic and simmering until thick.
• Uses: Perfect for burgers, grilled meats, cheese boards, roasted vegetables, and even breakfast dishes.
• Storage: Keeps in the fridge for up to a week, can be frozen for three months, or canned for up to a year.

The secret lies in patience during the caramelization process and using quality ingredients like aged balsamic vinegar and extra virgin olive oil. Whether refrigerated, frozen, or canned, this relish is a convenient way to enhance meals with bold, balanced flavors.

Ingredients and Equipment

Core Ingredients

To make 2–3 cups of onion relish, you'll need: 3–4 large onions (about 2–2½ lbs), ½–1½ cups balsamic vinegar, ½–1½ cups sugar (brown or granulated), ½–2 tsp salt, ½–1 tsp pepper, and 1–2 tbsp olive oil.

The type of onion you pick will define the flavor. Sweet or yellow onions, like Vidalia, create a mellow, jam-like relish. Red onions deliver a stronger, sharper taste with a darker color, while white onions require extra sugar to offset their bite.

Balsamic vinegar is the star ingredient here. Dark balsamic vinegar offers a rich, syrupy texture and deep sweetness, while white balsamic adds a lighter, tangy note. For a standout option, try Big Horn Olive Oil's Traditional 18-Year Aged Dark Balsamic Vinegar ($8.99), which has rich dried fruit and oak undertones, reducing the need for extra sugar.

Sugar serves two purposes: it helps caramelize the onions and balances the vinegar's acidity. Brown sugar adds a molasses-like depth and a darker finish, while granulated sugar provides a cleaner, simpler sweetness. You can also swap in honey or maple syrup for part of the sugar to add more layers of flavor, but keep an eye on the heat, as these sweeteners brown faster.

Olive oil sets the stage for cooking. Big Horn Olive Oil's Ultra Premium Extra Virgin Olive Oils (like Estate Reserve, Picual, or Coratina, priced at $8.99) offer fruity, peppery notes and a high smoke point (410°F), perfect for controlled caramelization.

To make the relish your own, consider adding optional ingredients for extra flavor.

Optional Add-Ins

You can customize your relish with some additional ingredients.

• Garlic: Add 1 to 3 minced cloves after the onions have softened but before adding the balsamic vinegar. Cook for 1–2 minutes until fragrant, but avoid burning it.
• Fresh herbs: Thyme or rosemary work well. Use 1–2 tsp finely minced, or 2–3 whole sprigs, during the final simmer. For a more layered flavor, try adding summer savory or a thyme-rosemary mix (about 2 tbsp finely minced per 4 lbs of onions). Bay leaves (1–2) can be added early but should be removed before serving.
• Chili flakes: Add ½–1 tsp with the vinegar and sugar for a subtle heat. You can also increase the black pepper to ½–1 tsp toward the end for a spicier kick.

Timing is everything with these add-ins. Herbs and spices should go in during the simmering stage, allowing their flavors to blend without overpowering the onions' sweetness or the balsamic's depth.

Required Equipment

The right tools make all the difference for even caramelization and rich flavor. A large, heavy-bottom skillet, sauté pan, or Dutch oven (5-quart or larger) is essential. Heavy materials like cast iron, enameled cast iron, or stainless steel distribute heat evenly, preventing hot spots that can scorch the onions or sugar. A wide surface area also allows moisture to evaporate efficiently, helping the onions caramelize instead of steam.

Enameled cast iron or stainless steel pans are ideal for cooking with acidic balsamic vinegar. Avoid bare aluminum, which reacts with acids. Choose a pan wide enough to ensure the onions form no more than a 1- to 1½-inch layer - this helps them brown evenly and cook faster. Thin or small pans can lead to uneven cooking, burning, and longer cook times.

For prep, a sharp chef's knife (6 to 8 inches) is perfect for slicing onions evenly. Uniform slices ensure the onions cook at the same rate. If you're making a large batch, a mandoline slicer can save time and produce consistent, thin slices that help achieve a smooth, jammy texture. Just be sure to use cut-resistant gloves for safety. Pair your knife or mandoline with a large, sturdy cutting board (wood or plastic) that provides enough space for multiple sliced onions.

When it comes to storage, glass jars with tight-fitting lids are your best bet. Mason jars or other heat-safe options work well for refrigeration or canning. For short-term storage (1–2 weeks), clean jars with screw-top or clamp lids are fine. If you plan to can your relish for long-term storage, use proper canning jars with two-piece lids. Always check for chips or damage to ensure a good seal.

Other handy tools include a wooden spoon or heat-resistant spatula for stirring without scratching your pan and a ladle or wide-mouth funnel to transfer the hot relish into jars without spills. With these essentials, you're all set to turn simple onions into a rich, flavorful condiment.

Step-by-Step Instructions

Preparing the Onions

Start by choosing 3–4 large onions, roughly 3–4 pounds in total. Use a sharp chef's knife for this task - dull knives crush the onion cells, releasing more of those tear-inducing compounds we all dread. Cut each onion in half lengthwise, going through the root end, and place the halves cut-side down on your cutting board. This keeps the onion steady and makes the process safer for your fingers.

Next, trim off the stem end and peel away the outer layers of skin. Slice the onions into uniform half-moons, about 1/8 to 1/4 inch thick. Keeping the slices consistent helps them cook evenly, so you won’t end up with some pieces burnt while others stay raw.

If cutting onions makes your eyes water, try chilling them in the fridge for about 30 minutes beforehand. Another trick is to position your cutting board near a fan or vent to pull the onion fumes away from your face. Work steadily, keeping the cut sides facing downward as much as possible to limit exposure.

Once your onions are sliced, you're ready to caramelize them.

Caramelizing the Onions

Grab a large, heavy-bottomed skillet, sauté pan, or Dutch oven, and heat it over medium-low heat. For 3–4 pounds of onions, you’ll need about 2–4 tablespoons of extra virgin olive oil - just enough to lightly coat the pan. A high-quality olive oil, like Big Horn Olive Oil's Ultra Premium Extra Virgin Olive Oils, can elevate the onions' natural sweetness.

When the oil starts to shimmer, add all the sliced onions. Stir gently to coat them evenly in the oil, then let them cook undisturbed for a few minutes. You want a steady, gentle sizzle - too hot, and the onions will brown too quickly on the outside while staying raw inside; too cool, and they’ll steam instead of caramelizing.

Let the onions cook for 30–60 minutes, stirring more frequently as they begin to color. Adjust the heat as needed and add a teaspoon of water if they start browning too fast. Your goal is a deep amber-brown color and a jam-like texture. If you notice dark spots forming or smell anything acrid, lower the heat and deglaze with a little water to loosen the browned bits. On the flip side, if the onions are too wet and steaming, increase the heat slightly or leave the pan partially uncovered to let excess moisture escape. Patience is key here - rushing will only lead to burnt, bitter onions instead of the rich, sweet caramelized flavor you’re aiming for.

Deglazing with Balsamic Vinegar

When your onions are soft and have reached that beautiful deep golden-brown hue, it’s time to deglaze the pan. Briefly increase the heat to medium and pour in balsamic vinegar - about 1/3 to 1 1/2 cups for 3–4 pounds of onions, depending on how tangy and saucy you want your relish. For a richer flavor, go for a well-aged balsamic vinegar, like Big Horn Olive Oil's Traditional 18-Year Aged Dark Balsamic Vinegar ($8.99). Its subtle dried fruit and oak undertones, along with a naturally sweeter, thicker profile, will add depth to your relish.

The vinegar will sizzle and steam as it hits the hot pan. Use a wooden spoon or heat-resistant spatula to scrape up the browned bits from the bottom of the pan - this is where tons of flavor lives. Once the fond is incorporated, lower the heat and stir in sugar (about 1/2 to 1 1/2 cups, depending on your taste). Let the mixture simmer gently for 15–60 minutes, depending on the amount of liquid and the thickness you’re aiming for.

As the relish thickens, stir it occasionally to prevent sticking, increasing the frequency as it gets closer to your desired texture. A simple test: drag a spoon through the mixture - if you can briefly see the pan’s bottom before the relish fills back in, you’re almost there. Keep in mind that the relish will thicken further as it cools, so stop cooking when it’s slightly looser than your ideal final texture.

When your relish is thick and glossy, remove the pan from the heat. Taste and adjust the flavor with more vinegar, sugar, salt, or pepper if needed. Let it cool for 5–10 minutes before transferring it to clean, heat-safe jars or containers. Pack the relish while it’s still warm to help it settle evenly. Allow it to cool to room temperature uncovered or loosely covered to avoid condensation thinning the mixture. Once cooled, seal the jars and refrigerate. As it chills, the flavors will deepen, and the texture will firm up, making it perfect for spreading on burgers, sandwiches, cheese boards, or as a topping for grilled meats.

Flavor Balancing and Serving Ideas

Balancing Flavors

Once you've carefully cooked your caramelized onion relish, the next step is perfecting the balance of flavors. A great relish should deliver three key elements: sweetness from the slow-cooked onions and sugar, tanginess from the balsamic vinegar, and a savory depth from salt, pepper, and any herbs you’ve added. The sweetness should stand out, but not overwhelm, while the acidity cuts through the richness to keep the relish vibrant and layered. Ideally, you’ll taste a progression of flavors - starting with the sweet, jammy onions, followed by a mild balsamic tang, and finishing with a savory note that complements a variety of foods like meats, cheeses, and vegetables.

Fine-tuning the flavor is all about small adjustments. If it’s too sweet, add 1–2 teaspoons of balsamic vinegar and simmer for a few minutes to mellow it out. If the acidity feels overpowering, simmer longer to reduce the sharpness, or stir in a teaspoon or two of sugar. If the flavors seem dull or flat, a pinch of salt and a bit of freshly ground pepper can bring everything to life.

When seasoning, start light. Taste the onions after caramelization to gauge their natural sweetness before adding all the vinegar. Once the balsamic is in and reduced, taste the relish warm - but not hot - as high temperatures can make flavors harder to judge. Adjust in this order: salt first, then acidity (balsamic), followed by sweetness (sugar or honey), and finally optional spices or herbs. Let a small spoonful cool for a minute or two before tasting for the most accurate flavor profile.

You can also tweak the recipe to suit different tastes or dishes. For a richer sweetness, swap white sugar for brown sugar or use honey or maple syrup. For a brighter tang, mix balsamic vinegar with red wine vinegar or apple cider vinegar. Herbs like thyme, rosemary, or bay leaves (remove the bay leaf before serving) add an earthy depth, while smoked paprika brings a subtle smokiness that pairs beautifully with grilled meats. A pinch of red pepper flakes or chili can add gentle heat - just increase in small increments and taste as you go.

Using a high-quality balsamic vinegar can make a big difference. Brands like Big Horn Olive Oil offer flavored balsamic vinegars such as Blood Orange, Sicilian Lemon, Mango, Blackberry Ginger, and Cinnamon Pear. These can introduce unique sweet, tart, or spicy notes to your relish. For an extra touch of richness, finish the relish with a drizzle of their Ultra Premium Extra Virgin Olive Oil - it adds both flavor and a glossy finish.

Once the flavors are balanced to perfection, it’s time to think about how to serve this versatile condiment.

Serving Suggestions

Caramelized onion relish is a kitchen multitasker, enhancing everything from casual meals to elegant appetizers with its rich, complex flavor.

For sandwiches and burgers, spread it on grilled cheese, turkey, roast beef, or steak sandwiches. It adds moisture and depth without making the bread soggy, especially when layered under the cheese. On burgers, it transforms a simple patty into something gourmet.

On cheese boards and charcuterie, it pairs beautifully with sharp cheddar, aged gouda, blue cheese, brie, or goat cheese. Its sweet-tart flavor balances salty, creamy, and bold cheeses. Serve it in a small bowl with a spoon alongside crackers or baguette slices. For crostini or bruschetta, top toasted bread with soft cheese like goat cheese, ricotta, or brie, then add a spoonful of relish. A drizzle of premium balsamic or olive oil makes a great finishing touch. The relish also complements cured meats like salami, prosciutto, and pâté, cutting through their richness.

For grilled meats and proteins, use the relish as a topping for steak, pork chops, grilled chicken, or lamb. It acts as a built-in sauce, adding sweetness and acidity that enhance the smoky, savory flavors. It’s also a delicious upgrade for hot dogs and sausages.

For vegetarian dishes, spoon it over roasted vegetables like Brussels sprouts, carrots, green beans, or cauliflower just before serving. The sweetness enhances the caramelized edges, while the acidity brightens the dish. It also works well in grain bowls - mix it with quinoa, farro, or brown rice, along with roasted veggies and beans or tofu, for a flavorful, cohesive meal. Even breakfast gets a boost - add the relish to scrambled eggs, omelets, or breakfast sandwiches to give them a café-quality twist.

When serving, adjust the portion to suit your dish. For delicate foods like brie, goat cheese, or mild chicken, start with 1–2 teaspoons per serving to avoid overpowering the flavors. For bold pairings like blue cheese or cured meats, a slightly sweeter batch works well. And for hearty red meats, a tangier version with extra balsamic vinegar balances the richness.

One of the best things about this relish is its flexibility. You can make it several days in advance, store it in the fridge, and simply bring it to room temperature when you’re ready to serve. This make-ahead convenience makes it perfect for both weeknight meals and entertaining, letting you enjoy its flavor without any last-minute stress.

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Storage and Make-Ahead Tips

Refrigerated Storage

Caramelized onion relish is a fantastic make-ahead option, perfect for busy weeknights or planned gatherings. After cooking, let the relish cool to room temperature before transferring it to sterilized glass jars - Mason jars with tight-fitting lids work great. Cooling the relish first is key, as it prevents condensation inside the jar, which could lead to spoilage.

Once sealed, store the jars in the refrigerator at 40°F or below. Properly stored, your homemade relish will stay fresh for up to one week. In fact, the flavor improves after 24 hours as the sweetness of the onions blends with the tanginess of the balsamic vinegar and any added herbs or spices. This makes it an ideal condiment to prepare a few days in advance.

To ensure freshness, always use a clean spoon when scooping out the relish. Avoid double-dipping or introducing food particles, as this can lead to spoilage. Keep an eye out for signs that the relish has gone bad - such as an off smell, visible mold, discoloration, or gas bubbles - and discard the jar if you notice any of these. When serving at gatherings, don't leave the relish out at room temperature for more than two hours, as its high moisture and sugar content can encourage bacterial growth.

If the relish thickens too much during storage, you can gently reheat it on the stovetop over low heat, adding a splash of water or balsamic vinegar to adjust the consistency. Alternatively, warm it in the microwave in 15–20 second bursts, stirring between each interval. Serve it warm, room temperature, or straight from the fridge, depending on your preference and the dish you’re pairing it with.

For longer storage, consider freezing or canning, as detailed below.

Canning and Freezing

If you want to store your relish for more than a week, freezing or water-bath canning are excellent options, each with its own benefits.

Freezing is the simpler method and works well if you’re making the relish weeks or months in advance. Once cooled, portion the relish into freezer-safe containers or heavy-duty zip-top bags, leaving about half an inch of space for expansion as it freezes. Don’t forget to label each container with the date and contents. Properly frozen caramelized onion relish will retain its quality for up to three months. When ready to use, thaw it overnight in the refrigerator and reheat gently or serve as-is. While freezing slightly softens the texture, the flavor remains intact, making it perfect for spreads, sandwiches, and toppings.

Water-bath canning provides long-term storage, keeping your relish shelf-stable for up to 12 months when done correctly. Since onions are low in acid, achieving a safe pH level depends on the balsamic vinegar. It’s essential to follow tested recipes to ensure safety and prevent harmful bacteria like botulism.

Before starting, set up your canning equipment. Sterilize jars by washing them in hot, soapy water and keeping them warm. Ensure jar rims are clean and undamaged. When the relish is hot and ready, ladle it into the jars, leaving about ¼ inch of headspace. Wipe the rims clean, place the lids on, and secure the rings without overtightening. Use a jar lifter to lower the jars into a boiling water bath, ensuring they’re submerged by at least an inch of water. Process for 10 minutes if you’re at an elevation of 0–1,000 feet, adding one minute for every additional 1,000 feet.

After processing, let the jars cool on a towel-lined counter for 12–24 hours. Listen for the satisfying "pop" of the lids sealing. A properly sealed lid will be slightly indented in the center. Press the lid to test the seal - if it doesn’t flex or pop, it’s sealed. Store sealed jars in a cool, dark place, away from sunlight, which can degrade flavor and color over time. Any unsealed jars should be refrigerated and used within a week.

Storage Methods at a Glance

Using premium ingredients like Big Horn Olive Oil's Ultra Premium Extra Virgin Olive Oil and aged balsamic vinegar from Modena, Italy, enhances the relish’s flavor and shelf life. These high-quality vinegars add depth that only gets better as the relish sits and the flavors meld.

Whether you refrigerate, freeze, or can your caramelized onion relish, preparing it ahead of time simplifies meal prep and entertaining. Spend a quiet afternoon making a batch, and you’ll have a gourmet condiment ready to elevate cheese boards, sandwiches, or appetizers for weeks - or even months - to come.

How to Make Perfect Caramelised Balsamic Onions | The Ultimate Recipe

Conclusion

Making caramelized onion relish with balsamic vinegar might sound fancy, but it’s a straightforward process with delicious rewards. Start by slicing your onions evenly and cooking them slowly in good olive oil until they’re soft and golden. Then, deglaze the pan with balsamic vinegar to scrape up all those flavorful browned bits, and let it simmer until the mixture turns thick and syrupy. Add a pinch of salt and pepper, let it cool, and store it in clean jars. If canning, follow proper sterilization and processing techniques to keep your relish shelf-stable for up to a year.

The secret to success here? Patience. Rushing the caramelization process can leave you with burnt or mushy onions, but taking your time creates that rich, sweet, jam-like flavor. Stir occasionally to build up those caramelized bits (fond) that add incredible depth when mixed with the vinegar. Taste as you go, adjusting the balance of sweetness, acidity, and seasoning for the perfect flavor.

Using high-quality ingredients makes all the difference. For example, Big Horn Olive Oil’s Ultra Premium EVOO, with its high smoke point of 410°F or more, ensures you can caramelize without burning or introducing off-flavors. Pair it with authentic balsamic vinegar from Modena, and you’re set for a relish that tastes as amazing as it sounds. Big Horn Olive Oil’s commitment to freshness - shipping bottles within 1–3 months of harvest - guarantees you’re working with top-tier products.

Once you’ve mastered the basics, feel free to experiment. Try using red onions, swapping in alternative sweeteners, or adding a pinch of mustard seeds or red pepper flakes for a twist. For refrigerator batches, there’s plenty of room for creativity, but if you’re canning, stick to tested recipes to ensure safe acidity levels.

A typical batch using about 4 pounds of onions yields roughly 3–4 cups of relish. The flavor actually improves after a day or two in the fridge, so making it ahead is a smart move. Whether you store it in the fridge, freeze it, or can it, you’ll have a gourmet condiment ready to elevate any meal.

Grab your onions and balsamic, and get ready to create a relish that’s sure to impress. It’s a simple way to add a touch of homemade luxury to your favorite dishes.

FAQs

What’s the best way to store caramelized onion relish to keep its flavor and texture intact?

To keep your caramelized onion relish tasting great and maintain its texture, store it in an airtight container in the refrigerator. Be sure to let it cool completely before sealing to avoid condensation, which could impact its quality.

If you'd like to store it for a longer period, freezing is a great option. Use small, freezer-safe containers or resealable bags, and when you're ready to use it, thaw the relish in the refrigerator overnight. A quick stir after thawing will help bring back its consistency. Following these steps will ensure your relish stays flavorful and perfectly textured.

How can I add unique flavors to caramelized onion relish with balsamic?

There are plenty of ways to tweak the flavor of caramelized onion relish to match your preferences. Want it sweeter? Add a drizzle of honey or maple syrup. Craving something more savory? Toss in some fresh herbs like thyme or rosemary, or a pinch of smoked paprika for a hint of smokiness. If you’re a fan of heat, a sprinkle of red pepper flakes or some finely chopped chili peppers can bring a spicy edge.

For a richer, more complex taste, try incorporating high-quality balsamic vinegar. Big Horn Olive Oil offers Ultra Premium Balsamic Vinegars that can deepen the flavor of your relish. Their infused varieties, like fig or garlic balsamic, are perfect for creating a condiment that’s not just tasty but truly one of a kind!

Can I use different types of onions and balsamic vinegar to change the flavor of caramelized onion relish?

Choosing the right onion - be it sweet, red, yellow, or white - can dramatically shape the flavor of your relish. Sweet onions bring a mild and sugary touch, while red onions add a sharp yet slightly sweet bite. Yellow onions offer a balanced, savory depth, and white onions lean toward a crisp, tangy profile. The vinegar you use also plays a big role. Traditional balsamic vinegar provides a rich, classic sweetness, but trying infused varieties, like those from Big Horn Olive Oil, can introduce bold new flavors - think fruity hints or savory twists. Tweaking these ingredients lets you craft a relish that perfectly suits your palate!

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