What Is The Best Way to Sterilise Jars for Jams and Preserves?
We are often asked what method we recommend for sterilizing glass jars and bottles for home preserving.
While there are a number of favoured processes, the following one is very simple and normally very successful. This method has been used for many, many years with complete confidence and success.
- Always sterilise more jars or bottles than you think you will need, as it will be too late to prepare more containers when your product is ready to be packed.
- ALWAYS use new metal caps for optimum sealing, even if recycling jars or bottles. Used caps may not create a perfect seal, and may have small specks of rust which could spoil your product. Plastic caps are not intended for use with preserving, as they do not create a vacuum seal.
- All jars and bottles and their metal caps should be washed before use, in warm water with a mild detergent.
- Rinse in warm running water but do not dry them with a teatowel
- Alternatively, wash, rinse and dry your jars and caps in the dishwasher on its hottest setting
- Place warm jars standing upright, and metal caps upside down, in an oven pre-heated to 110-120oC, for about 15 minutes, to ensure they are completely dry and to keep them hot.
- When your product is ready to bottle, using suitable hand protection, remove a dry, hot jar from oven and immediately fill with boiling preserves. (Only take them from the oven one at a time) Leave a small gap between top of contents and rim of jar so that protective vacuum may form.
- Ensure there are no trapped air bubbles down the sides of the jar – use a skewer or similar, sterilised, utensil to release any bubbles
- Apply cap immediately, twisting to first stop – do not overtighten, as cap and seal may be damaged.
- As contents cools, a vacuum will be formed in the jar, preserving the contents for a long shelf life, particularly if sugar content is high.
- Seal is formed by the compound ring inside the lid sealing against the rim of the jar, and being held there by the vacuum, not by how tightly the cap is twisted on.
- Never add hot product to cold jars, or cold product to hot jars, as the jar may shatter. Always warm the jar gradually with tap water before placing in oven. Always ensure the jars and caps are completely dry and still hot before filling with content.
- Allow to cool at room temperature and store in a cool place out of direct light. If processed by each step of the method above, your product should have a shelf life of up to 12 months, or even longer.