Equipment
Ingredients
Jam Base
- 1000 g blueberries, washed, picked over for stems
- 600 g granulated sugar
- 60 ml lime juice, freshly squeezed
- 10 g lime zest, finely grated
Nutrition (per serving)
Method
Place the washed blueberries in a heavy-bottomed pot. Using a potato masher, gently crush about half of the berries to release their juices while leaving the rest whole for texture.
Add the granulated sugar, freshly squeezed lime juice, and lime zest to the crushed blueberries. Stir thoroughly to combine.
Allow the mixture to macerate at room temperature for 30 minutes. This draws out more moisture from the fruit and begins dissolving the sugar, preventing scorching.
Place the pot over medium-high heat. Stir constantly until the sugar is completely dissolved and the mixture comes to a full rolling boil.
Continue to boil rapidly, stirring frequently to prevent sticking at the bottom. Cook until the mixture reaches 105 degrees Celsius (220 degrees Fahrenheit) on a candy thermometer.
Remove the pot from the heat. Carefully skim off any excess foam from the surface using a metal spoon. Ladle the hot jam into sterilized glass jars, leaving about 1 centimeter of headspace at the top.
Wipe the rims clean, secure the lids, and let the jars cool completely at room temperature without disturbing them for 12 hours. The pectin requires undisturbed cooling time to set properly.
Chef's Notes
- Blueberries naturally contain very low levels of pectin. The addition of lime juice is scientifically crucial because its high acidity lowers the pH of the mixture to around 3.0, neutralizing negative charges on pectin molecules and allowing them to bond into a gel structure.
- Never attempt to double a jam recipe in the same pot. Increasing the volume drastically changes the evaporation rate, meaning your fruit will severely overcook and lose its fresh flavor before the syrup reaches the critical setting point.
- For a flawlessly smooth spread, you can use an immersion blender to puree the macerated mixture before cooking. Leaving the berries partially crushed, however, creates a beautifully rustic texture that looks spectacular on toasted sourdough.
- Skimming the foam at the end is purely aesthetic. The foam is just trapped air bubbles and fruit proteins, but removing it gives your finished jam a professional, jewel-like translucence.
Storage
Refrigerator: 3 months — Store in the refrigerator once a jar is opened.
Freezer: 6 months — Leave at least 2cm headspace if freezing in glass jars to prevent shattering.
