• Make sure to leave space at the top to allow for lots of fizzing, bubbling and boiling away.
How much headroom?
• Brined foods (including kraut) with liquid brine – 1-2″ headroom (larger jars, more headroom, smaller jars can have less).
• Thicker liquids such as condiments or kefir – 1/4 to 1/3 of the jar, can be left empty.
• Pastes and fairly solid foods – 1/2 of the jar to be left empty.
The more solid the food, the harder it is for air to escape.
The bubbles have a harder time working to the surface, so the food expands instead.