The inside of a Kilner preserve lid features two distinct components designed for food safety and vacuum preservation: a protective inner lacquer coating and a outer plastisol sealing ring.
1. The Inner Lacquer (The Barrier)
The main flat surface on the underside of the tin metal lid is coated with a food-grade enamel or protective lacquer.
- Purpose: This coating acts as an acid-resistant barrier. It prevents the natural acids and moisture in your preserves (like tomatoes, vinegars, or citrus fruits) from reacting with the raw tin metal, which would otherwise cause the lid to rust or corrode.
- BPA Status: In compliance with modern food safety regulations, major brands like Kilner use compliant, BPA-NI (BPA Non-Intent) or BPA-free inner linings to ensure no harmful chemicals migrate into your food.
2. The Sealing Ring (The Gasket)
Running along the outer edge of the lid's underside is a soft, flexible ring.
- Material: This is a PVC plastisol compound gasket.
- Purpose: When you heat the jars during a water bath process, this ring softens. As the jar cools down, the softened ring molds perfectly to the glass rim, hardening slightly to create the airtight vacuum seal necessary for long-term preservation.
This information was sourced from the website: "Healthy Canning."