Why & how to sterilise jars for jam, chutney, and pickles?
- To sterilise jars removes bacteria, yeasts and fungi that might spoil homemade preserves such as jams, chutneys or pickles. Without this step, spoilage or serious health risks like botulism may occur.
- Even new jars are not sterile. Always clean them thoroughly before use.
- If you use a proper water bath or pressure canning process, pre-sterilising jars may be unnecessary but only if the processing meets required times and conditions.
Safe methods to sterilise jars
Here are the best methods based on trusted guidance.
1. Water bath (boiling) method — most reliable
- Inspect each jar for chips or cracks and discard any that are imperfect.
- Wash jars and lids thoroughly in hot, soapy water and rinse well.
- Place jars in a saucepan suitable for canning and add cold water until jars are fully submerged.
- Bring the water to the boil and keep it rolling for at least 10 minutes. Add extra time if you are at high altitude.
- Use tongs to remove the jars and leave them warm until you are ready to fill them.
- For lids and rubber seals, do not boil. Simmer them gently for about 10 minutes to avoid damaging the seal.
Why this method is preferred
This is the gold standard to sterilise jars, and it can also act as the processing step if you water bath can your preserves according to the specified times and temperatures.
2. Dishwasher (high-temperature or sanitise cycle)
- Wash jars and lids in the dishwasher using a hot or sanitise cycle. Ensure no detergent residue remains.
- Time the end of the wash to coincide with when your preserve will be ready to fill so jars remain hot.
Note of caution
Use a dishwasher only if it includes a sanitise setting. Dishwashers may not reliably sterilise in every model and could harbour bacteria if not run correctly.
3. Oven method
Process
- Preheat your oven to around 160°C (gas mark 3).
- Wash jars and lids in hot, soapy water and rinse. Do not dry them completely.
- Place jars upside down on a baking sheet while still wet and heat for approximately 10 to 15 minutes.
- Remove seals or rubber rings before the oven. These are better sterilised by simmering.
Drawbacks
- Dry heat might not reliably destroy all bacteria.
- Ovens can have uneven temperatures and might harbour bacteria.
- Many food safety authorities advise against relying on the oven method for sterilisation.
4. Microwave method
- Wash and rinse jars, leaving them slightly wet.
- Microwave on high for 30 to 45 seconds. This method is not suitable for jars with metal parts or certain branded jars that advise against it.
Important warning
The microwave method is variable and risky. Microwaves heat unevenly and can cause superheating or jar breakage.
Summary table
| Method | Pros | Cons |
|---|---|---|
| Water bath (boiling) | Most reliable; can double as the canning process | Requires suitable pan, heat source and time |
| Dishwasher | Convenient if sanitise cycle is available | May not be fully reliable; risk of contamination |
| Oven | Simple to do | Not recommended by some experts; uneven heat |
| Microwave | Quick | Unsafe variability; limited to certain jars |
Recommended safe routine
- Inspect jars for damage and discard any unreliable ones.
- Clean thoroughly with hot, soapy water and rinse well.
- Sterilise jars by one of these methods, prioritising water bath as the safest:
- Water bath (best overall)
- Dishwasher (if you have a sanitise cycle)
- Avoid oven or microwave unless you clearly note the risks to readers.
- Keep jars warm until filling to prevent thermal shock and help sealing.
- Fill when hot, leave appropriate headspace, label and process accordingly.
Use sterlised jars when using the jam recipes