[rugbyman]

Just about to make a batch of beetroot chutney. Grow at my allotment. Have purchased some Kilner Jars with a vacuum seal but , I know this may sound a bit dumb, how do I make the vacuum. The instructions inside the jar are not all that clear.
Many thanks in advance for your help.

[plum crumble]

don't worry, it's not a dumb question at all. when you put the hot chutney into the warm sterilised jars and seal them, the chutney then cools down. The cooler contents, including the steam they were producing, take up less space in the jar. This reduction in size "sucks in" and creates the vacuum. 

[rugbyman]

Doh!  I should have listened at school. Thank you. 

[hamstergbert]

It will help if as soon as you have tightened the lids down you can stand a plank of wood or some such across the tops (even books at a push) and plonk bricks or other suitably heavy item on top to ensure the lids are firmly down during the cooling and contraction phase - some seals need a bit of a help like this if they have a slight tendency to pass.   Anything heavy will do - glat irons, pans of water, weight is the only thing that matters.  Once fully cooled the air gap and contents should have shrunk sufficiently to make a stable good seal (in recycled jam jars etc enough to suck down the telltale in the lid, and in the case of clip top kilners enough to withstand the clip being loosened, scret top kilners the metal lockring unscrewed and the glass top stays rock solid unless you tug at it sharply).

Before starting of course make sure the seals are well washed and free of any bits of grit etc that would reduce the seal gastight integrity.