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PRE-HEATING CANNING JARS

Glass jars do not require sterilisation (boiling jars for 10 minutes) if the water bath (or steam canner) processing time is 10 minutes or more - or if you are pressure canning. For processing times under 10 minutes, sterilise jars in the water bath canner (filled with water) by boiling for 10 minutes (see chart below with sterilisation time for different altitudes), before filling with your hot pre-prepared food. Alternatively, if your processing time is 5 minutes, you could increase your water bath processing time to 10 minutes and skip the sterilisation step!
 
Sterilisation Time
Altitude (feet)
Altitude (metres)
10 minutes
0 – 1000 feet
0 - 300 metres
11 minutes
1001 – 2000 feet
301 – 600 metres
12 minutes
2001 – 3000 feet
601 – 900 metres
13 minutes
3001 – 4000 feet
901 – 1200 metres
14 minutes
4001 – 5000 feet
1201 – 1500 metres
15 minutes
5001 – 6000 feet
1501 – 1800 metres
16 minutes
6001 – 7000 feet
1801 – 2100 metres
17 minutes
7001 – 8000 feet
2101 – 2400 metres
18 minutes
8001 – 9000 feet
2401 – 2700 metres
19 minutes
9001 – 10000 feet
2701 – 3000 metres
 
It is recommended to pre-heat jars (i.e. warm jars up in hot water, no boiling required – boiling is up to you). Unsure if jars are high quality, tempered glass? Pre-heating is recommended to reduce the risk of thermal shock (sudden expansion/shrinking when cold jars are filled with a hot preserve, or vice versa). Jars can be pre-heated in a water bath canner, dishwasher or sink full of hot water.
 
Jars (including lids and seals) are not sterile out of the packaging – even if they are brand new. Jars or lids may have glass residue, dust, or a bug/pest in the packaging for example. A quick, hot rinse (soapy water first, then just hot water) of all jars prior to use in preserving is recommended – via dishwasher or by hand. Lids and seals are best rinsed by hand in hot water.
 
Do not boil the lids/seals – this can reduce the effectiveness of the sealing compound inside the lid/seal. Lids and seals can be used at room temperature, or slightly warmed for a few minutes in hot water (not on heat) if you prefer. Jar rings (i.e. mason jar rings) and jar clips do not require boiling either, as they do not come into contact with any preserve. Ensure they are clean before use though. Jar gaskets (rubber rings) do not require boiling but do need to be soaked in warm water prior to adding to prepared jars.
 
As educators, we must teach the safest technique to ensure high quality preserves and help jars to last for years (or generations). We recommend warming jars up as explained above. Jars are not recommended to be warmed via a microwave or oven.
 
Author: Megan Radaich
Image Credit: Megan Radaich
Publication: www.foodpreserving.org

Acknowledgement 
Kaya Wanjoo. Food Preserving kaditj kalyakoorl moondang-ak kaaradj midi boodjar-ak nyininy, yakka wer waabiny, Noongar moort. Ngala kaditj baalap kalyakoorl nidja boodjar wer kep kaaradjiny, baalap moorditj nidja yaakiny-ak wer moorditj moort wer kaditj Birdiya wer yeyi.
Hello and Welcome. Food Preserving acknowledges the Traditional Custodians of the land on which we live, work and play, the Nyoongar people. We recognise their connection to the land and local waterways, their resilience and commitment to community and pay our respect to Elders past and present.
 
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