How do food jar factories put negative pressure into the jar to begin with?

Question

How do food jar factories put negative pressure into the jar to begin with?

In: 87

Answer 1

Food jar factory’s actually cook the product partially in the jars and seal it before cooling down. The cooling of the air causes the vaccuum. But if bacteria get ahold of the content the actually produces methane or other gasses which causes the pressure be normal or positive.