I think the fermentation is probably doing that... like any fermented plant it lets off gasses. Thats gotta be what's making them lose the vacuum... Good idea to check them regular like. But yes, they do also shrink a bit so that will do it as well. morning Dr. DMine sometimes seem to shrink slightly or something that looks like a blown seal but it’s not. After the first couple times I now double-triple verify the seals. It doesn’t always happen but has happened a few times. I now inspect them daily looking for any excuse to open and reseal.