Mixed Berry Jam with Juniper & Lime

Learn how to make mixed berry jam with award-winning preserves maker Jacqueline Morris, owner of Perfectly Preserved.

Made with frozen mixed berries, lime and juniper, this simple homemade jam has a fresh, tart flavour and can be made at any time of year. Monitoring the temperature as it cooks helps you achieve the right set and consistency.

What Temperature Does Jam Set At?

Around 105 °C is the traditional setting point for jam. However, the exact temperature can vary depending on the recipe and the balance of fruit, sugar, pectin and acid.

For this mixed berry jam, Jacqueline recommends 103-105 °C. Aim for the lower end for a softer set, or closer to 105 °C for a firmer consistency.

Jam Temperature Guide

Why Does Jam Set at Around 105 °C?

As jam boils, water evaporates, and the fruit and sugar become more concentrated, causing the boiling temperature to rise.

Reaching around 105 °C is a useful indication that a traditional jam has reached the concentration needed to set as it cools.

About Jacqueline Morris

Jacqueline Morris is the owner of Perfectly Preserved and a 2020 Double Gold Artisan Marmalade Award winner.

Jacqueline makes small batches of jams, jellies, marmalades, caramels, curds and chutneys from her home in West Sussex, combining seasonal ingredients with interesting flavour combinations.

We welcomed Jacqueline to the Thermapen kitchen to see her jam-making in action and learn her tips for getting the perfect set.

Jacqueline says:

“I love using my Thermapen when I'm making jam as I can check the temperature instantly and accurately. My jam sets perfectly every time.”

Mixed Berry Jam Recipe

Frozen berries mean you can make this recipe at any time of year. Lime adds freshness, while crushed juniper berries bring a distinctive aromatic flavour.

For an optional twist, add a little gin before sealing the jars.

Ingredients

• 1kg frozen mixed berries

• 700–800g granulated sugar

• Juice and zest of 2 limes

• 1 tsp juniper berries, crushed

• Gin (optional)

Method

1. Sterilise Your Jars

You'll need around six 190ml jars, or a mixture of different sizes.

Run the jars and lids through a hot dishwasher cycle shortly before you need them, then leave them to air dry.

Alternatively, wash the jars and lids in hot water, then place them in an oven at 140 °C / 120 °C fan / gas mark 1 for 15 minutes. Switch off the oven and leave them inside until you're ready to fill them.

2. Cook the Fruit

Add the frozen berries to a large, heavy-bottomed pan, followed by the lime juice, zest and crushed juniper berries.

Heat gently until the fruit softens and releases its juices.

3. Add the Sugar

Add the sugar a third at a time, stirring gently with a wooden spoon until it has completely dissolved.

Check the bottom of the pan with your spoon. It shouldn't feel grainy before you move on to the next stage.

4. Bring the Jam to Setting Temperature

Increase the heat and bring the mixture to a steady boil.

After around 5–6 minutes, start checking the temperature regularly with your Thermapen.

For this recipe, Jacqueline recommends 103-105 °C. Aim for the lower end for a softer set, or go closer to 105 °C for a firmer consistency.

Remove the pan from the heat once you've reached your desired temperature.

5. Remove Any Scum

Once off the heat, stir the jam gently and slowly in one direction to help disperse any scum.

Skim any remaining scum from the surface with a slotted spoon.

6. Cool Slightly Before Potting

Allow the jam to cool slightly before filling your jars. This helps prevent larger pieces of fruit from floating to the top.

Jacqueline recommends potting this recipe before the temperature falls below 87 °C.

7. Fill Your Jars

Using a heatproof jug or ladle and funnel, carefully fill your sterilised jars and put the lids on immediately.

For a boozy version, add a teaspoon of gin to each jar before sealing.

Leave the jars to cool completely before labelling.

How to Store Homemade Jam

Store unopened jars in a cool, dark and dry place. This mixed berry jam is best enjoyed within nine months.

Once opened, keep the jam refrigerated and use within 2–3 months.

Jam-Making FAQs

What is the jam setting temperature?

Around 105 °C is the traditional setting point for jam, but the exact temperature can vary slightly by recipe.

For Jacqueline's mixed berry jam, aim for 103-105 °C, depending on how firm you'd like the finished set to be.

Why does jam need to reach 105 °C?

As jam boils, water evaporates, and the fruit and sugar become more concentrated. This raises the boiling temperature.

Reaching around 105 °C is a useful indication that traditional jam has reached the concentration needed to set properly once cooled.

How do you know when jam is ready?

Checking the temperature is one of the simplest ways to monitor when your jam is approaching its setting point.

Use a fast-reading food thermometer as it boils and follow the target temperature specified in your recipe.

Remember that jam continues to set as it cools, so don't judge the final consistency while it's still hot.

Why Isn't My Jam Setting?

A good jam set relies on the right balance of fruit, sugar, pectin, acidity and concentration.

First, allow the jam to cool completely, as it will continue to thicken as it cools. If it's still too runny, return it to the pan and bring it back to a boil, checking the temperature as it cooks.

If it still won't set, check your recipe, as it may need additional pectin or acid, such as lemon juice.

Can You Overcook Jam?

Yes. Cooking jam for too long can result in a firmer set than intended and can affect the finished flavour and texture.

As you approach your target temperature, check it regularly so you can remove the pan from the heat at the right point.

Why Use a Thermometer for Jam?

Cooking time alone can't tell you when jam has reached its setting point. The quantity you're making, the recipe and the heat of your hob can all affect how quickly it cooks.

Using a fast, accurate thermometer like a Thermapen lets you monitor the temperature directly and remove the jam from the heat when it reaches the target for your recipe.

Get the Set Just Right

Whether you're making jam, marmalade or another preserve, monitoring the temperature is a simple way to know when your mixture is approaching its setting point.

A fast-reading Thermapen makes it easy to check the temperature throughout the cook, helping you achieve the consistency you're looking for.