South African Tomato Red Onion Relish

You know that smell when vinegar hits a hot pan and suddenly the whole kitchen smells like a professional deli? That's the first thing that happens here. There's a specific point where the raw, biting scent of the red onions mellows out and starts smelling like a sweet, savory jam.

I used to just buy the store-bought stuff, but it always tasted like corn syrup and preservatives. Once I tried making a homemade version, I realized the difference is all in the texture. You get these distinct little bits of tomato and softened onion that give the dish a real bite.

This Tomato Red Onion Relish is basically a plant based powerhouse. It’s vibrant, colorful, and has a sharp tang that makes everything it touches taste fresher. Trust me on this, once you have a jar in your fridge, you'll find excuses to put it on everything.

The Trick Behind the Texture

Red Onion Anthocyanins: Red onions have natural pigments that break down into a rich, dark color when cooked. This creates a jammy consistency and a mellow sweetness you just don't get with white onions.

Sugar and Acid Balance: The brown sugar doesn't just make it sweet, it helps the vinegar cling to the vegetables. This prevents the relish from becoming a watery soup and keeps it thick.

Slow Reduction: Simmering for 45 minutes allows the water in the tomatoes to evaporate. This concentrates the flavor and gives the relish that concentrated, bold punch.

Tools for the Job

Keep your equipment simple. A large, heavy bottomed saucepan is essential here, as a thin pot may cause the sugar to scorch before the tomatoes have fully broken down.

Use a sharp blade for the dicing to ensure the pieces are uniform, which allows them to soften at the same rate. Avoid the temptation to use a food processor; the goal is a chunky relish, not a puree.

Everything You'll Need

The Vegetable Base

• 2 lbs (900g) firm red tomatoes, finely diced Why this? Firmer varieties maintain their texture during simmering
• 2 cups (300g) red onion, finely diced Why this? Creates a deep mahogany hue and sweet base
• 2 cloves (6g) garlic, minced Why this? Adds a layer of savory depth

The Tang and Sweet

• 1 cup (240ml) apple cider vinegar Why this? Gentler than white vinegar, pairing better with fruit relishes
• 1/2 cup (100g) brown sugar, packed Why this? Molasses notes pair perfectly with the onions
• 1 tbsp (15ml) lemon juice Why this? Gives the final product a bright, crisp acidity

Seasonings

• 1 tsp (6g) sea salt Why this? Helps draw moisture from the vegetables
• 1/2 tsp (1g) black pepper, freshly ground Why this? Adds a mild, earthy warmth
• 1/4 tsp (1g) red chili flakes Why this? A small amount of heat to counter the sugar

Quick Recipe Specs

Since we're making this from scratch, it's helpful to see how it compares to the shortcut versions you find at the store.

Right then, let's look at the timing. This takes 10 minutes of prep and 45 minutes of cooking, making the total time 55 minutes. It serves about 8 people, depending on how generous you are with the scoops.

Key Cooking Steps

Preparing the Ingredients

Cut your red onions and tomatoes into consistent 1/4 inch cubes. While this is the most time consuming step, it ensures that everything cooks evenly. For exceptionally juicy tomatoes, you may want to remove some of the seeds first.

Simmering and Reducing

Place the cubed tomatoes, onions, and minced garlic into a large saucepan. Mix in the apple cider vinegar, brown sugar, sea salt, black pepper, and red chili flakes.

Set the heat to medium high and bring the mixture to a boil. As soon as it begins to bubble, immediately drop the heat to a simmer. Allow the relish to bubble gently for 35–45 minutes. You are looking for the liquid to reduce by half and the onions to turn a translucent, mahogany color.

Checkpoint 1

Around the 20-minute mark, the mixture will still resemble a soup. Keep simmering.

Checkpoint 2

By 35 minutes, the texture should become thick and glossy.

Checkpoint 3

The finished product should have a thick, spoonable, jam-like consistency.

Final Steps

During the last 2 minutes of cooking, stir in the lemon juice. This brightens the flavors that may have dimmed during the long simmer.

Take the pan off the heat and let the relish cool down slightly; you will notice it thickens further as it rests. Once the steam has subsided, transfer the relish into sterilized glass jars.

Solving Common Problems

Achieving the perfect consistency for a relish can be tricky. The main variable is the moisture in your tomatoes; specifically, very ripe or soft varieties may require extra time for the liquid to reduce.

Relish too watery

If the mixture is too thin, it's likely due to overly juicy tomatoes or insufficient heat. Simply continue simmering without a lid for an additional 10–15 minutes to encourage evaporation.

Too much acidity

To balance a vinegar profile that feels too sharp, stir in a teaspoon of honey or brown sugar right before finishing. This cuts the acidity without turning the relish into a sweet preserve.

Missing onions

If the onions have melted away, they were probably chopped too finely or cooked for too long. Aim for a precise 1/4 inch dice in future batches.

Adjusting the Batch Size

Scaling this Tomato Red Onion Relish for a large group is straightforward. For 2x or 4x batches, avoid simply quadrupling the salt and chili flakes. Instead, increase the seasonings to 1.5x first, then taste and add more if necessary.

You will need a wider pot when increasing the volume. If the pot is too deep, the liquid won't evaporate as efficiently, and you'll end up simmering for longer than 45 minutes. Consider working in batches if you don't have a commercial sized pot.

For a half sized batch, use a smaller saucepan to prevent the vinegar from evaporating too rapidly. You may need to shorten the cooking time because there is less mass to heat up.

Storage and Scrap Tips

Store the finished relish in a tight fitting glass jar within the refrigerator. It will remain fresh for roughly 2 weeks, as the sugar and vinegar naturally act as preservatives.

If you need it to last longer, try water bath canning. This method makes the relish shelf stable for several months, provided your jars are thoroughly sterilized to prevent spoilage.

I advise against freezing this recipe. The combination of water and vinegar often ruins the texture, leaving the tomatoes mushy after thawing. Your best bet is to prepare a large quantity and keep it chilled.

To minimize waste, save your onion skins and tomato ends. Store them in a freezer bag and, once full, simmer them in water to create a flavorful homemade vegetable stock.

Trying Different Flavors

Once you've got the base down, you can play with the profile. For a South African style, add a pinch of curry powder during the simmer. This makes it the classic accompaniment for boerewors rolls.

If you want a bit more depth, try a balsamic swap. Replace half of the apple cider vinegar with balsamic vinegar. This makes the relish darker and more syrupy, which is great for cheese boards.

For those following a keto diet, you can swap the brown sugar for a monk fruit or erythritol blend. Be careful with the amount, as some sweeteners can leave a cooling aftertaste when reduced.

For a spicier kick, double the red chili flakes or add a finely diced habanero at the start. The sweetness of the red onions balances the heat beautifully.

Best Food Pairings

This relish is incredibly versatile. It’s a powerhouse on a grilled burger, especially if you pair it with a copycat burger spread for a mix of creamy and tangy.

For a Braai: Serve it on top of grilled boerewors in a toasted roll. The acidity cuts right through the richness of the sausage.

For a Cheese Plate: Pair it with a sharp cheddar or a creamy brie. The sweetness of the red onions acts like a chutney.

For Dinner: Try it as a topping for grilled chicken breasts or roasted pork loin. It adds a vibrant pop of color and a sharp contrast to the savory meat.

Decision Shortcut:

• For a thicker jam: Simmer 10 minutes longer.
• For more heat: Double the chili flakes.
• For a brighter taste: Add an extra tsp of lemon juice.