How to sterilise jam jars

UK and US methods, side by side

The two methods belong to two different ways of making jam, so follow one or the other from start to finish rather than mixing their steps.

The Food Standards Agency doesn’t publish a jar-sterilising method for home jam, so the British column follows the BBC’s widely used cookery guidance. The US column is the USDA Complete Guide to Home Canning method, published by the National Center for Home Food Preservation (NCHFP).

Do you need to sterilize jars for canning?

Only when the processing time is short. NCHFP: “All jams, jellies, and pickled products processed less than 10 minutes should be filled into sterile empty jars.” Most jams and jellies are processed 5 minutes at sea level, so their jars are sterilised. Jars for foods processed 10 minutes or longer, such as the tested chutneys or apple butter in quarts, don’t need it: the processing does the work. The University of Georgia’s orange marmalade even gives two times: 5 minutes in sterilised jars or 10 minutes in clean, hot ones. NCHFP adds that sterile jars are preferred for low-pectin fruits, because the extra 5 minutes may weaken the gel.

Lids, dishwashers and the open-pan question

Use a new flat lid on every canning jar; the screw bands can be reused if they aren’t rusty, dented or bent. Prepare lids exactly as their maker directs. A dishwasher is fine for washing jars, but NCHFP is clear that washing doesn’t sterilise them, and that processing filled jars in a dishwasher, oven or microwave isn’t recommended.

That points to the real difference between the two columns. British open-pan jam is potted hot into hot, sterilised jars and sealed, with no further heating. USDA and NCHFP do not recommend this open-kettle approach, because it does not prevent all risks of spoilage; their tested recipes process the filled jars. Whichever you follow, store jars somewhere cool and dark, refrigerate after opening, and throw away any jar that grows mould.

What to put on a gift label

Edible Christmas gifts are lovely; just make sure the label says what someone needs to know. Put the name, the date it was made, and how to store it. For jars processed in a canner, NCHFP’s advice is a cool, dark, dry place at 50 to 70 °F (10 to 21 °C), best within a year, and in the fridge once opened, where regular jam is best used within a month. Reduced-sugar jams lose quality sooner (within 6 to 8 months), refrigerator spreads are used within 4 weeks, and freezer jam keeps up to a year frozen but about 3 weeks in the fridge. Listing the ingredients helps anyone avoiding a food.

Selling your jam

Selling is regulated, and this is general information, not legal advice. In England, Wales and Northern Ireland, the Food Standards Agency says a new food business, including one run from home, must register with its local authority at least 28 days before trading; registration is free. Anything sold as jam must also meet composition and labelling rules: England has The Jam and Similar Products (England) Regulations 2003, and Scotland, Wales and Northern Ireland each have their own. Your council’s environmental health team can say what applies to you.

In the US, cottage food laws are set state by state and vary widely: what you may sell, where, and what the label must say. The National Agricultural Law Center keeps a compilation of every state’s cottage food statutes (updated April 2025); check your state’s department of agriculture or health before your first market.

Worked examples

• A batch that makes 4 half-pints: 5 half-pint jars with one spare, 5 new flat lids and 5 bands.
• 2 litres of jam into 300 ml jars: 6 full jars and a part-jar, so 7, or 8 with a spare.
• Sterilising at 3,200 ft (975 m): 10 minutes plus 3, so boil the empty jars 13 minutes.

For the processing time after filling, use the canning time calculator; for the batch itself, the jam calculator. Bringing jars to a party? Kindred Picnic works out food quantities for the rest of the spread.