Glass jar cracked when trying to do the water bath sterilisation process

[Loka123]

On the label, it said for the jar, the water bath sterilisation process can be done which seems to be to put the glass jar into a pot of room temperature water and heat it on the stove until it becomes a rolling boil and then turn this off at 15 mins. Yet, the jars have a vertical crack (on the outside so the crack hasn't gone all the way to the inner surface) after me doing this disappointingly...

I had thought that the reason jars crack when boiling water is poured in is due to the thermal expansion due to sudden temperature change hence the slow and steady increase up to boiling yet still cracked..!

Anything I'm doing wrong?

Where did you get the jars? If they aren't proper, well made canning jars then they will crack when boiled. Always need to go with a good brand; not something cheap from a gimic gift set or random internet brand.
If they are old then the glass will weaken with time.

That's a bummer. Well made jars shouldn't do this. Afraid there ain't many cheap substitutes you can fall back on.

I had this problem with a kilner jar. I emailed them, sent photos and they sent me a replacement.

If it the odd single jar, then it just means an imperfection in that one which happens to the best of them. But if all of them cracked, then it's cheap glass that isn't designed for heating like that.

Do it in the microwave - add 1 tablespoon water to clean, empty jar and zap for 2 mins. Dip lids in just boiled water. Fill with whatever and put lids on. The button should suck down as contents cool to give a good seal. I do all my preserves this way. Try to time it so that the jars will be coming out of microwave just as contents ready to go in. Hot jar, hot contents. Works for me and far less faff than waterbath.

Thank you to all the people who replied - I didn't know what to think as this was the first time I had ever tried to sterilize a jar in this way and it cracked - so I guess there's not an error in my method, right? it's probably the quality/age of the jar itself (though this jar is very young - I bought it only a few months ago)?

@bluetrews25 ah great thank you for the tip. Although I'm trying to sterilize the jars for the intention to culture milk kefir rather than e.g. jam preservation so I might not be able to make use of your tip just yet.

Did you put a piece of fabric (teatowel or muslin for example) or similar between the jar and the pan? If not, it could have cracked because the bottom of the jar was in direct contact with the hot metal of the pan.

It still sterilises the jar in the microwave, and any jar will 'lose' the sterility when it is opened, so should be ok for you, though admittedly I'm not familiar with what you are suggesting!
I use ancient jars this way and never had one split. Used same ones for years.

I sterilise jars in the oven. Wash them and rinse them, put upside down in a cold oven, switch thermostat to 150C and leave them for 10 minutes once the temperature has been reached.