As our miso is unpasteurised, the culture is still alive, just dormant while refrigerated. Once the temperature of the miso increases (which happens in transit during warmer weather), the culture becomes more active again, restarting the fermentation process. As a result, gas is produced, as with all fermentation. This gas can then build up and push out any liquid that has found its way to the rim of the jar while in transit.

Unfortunately, we have no way to mitigate this. If we used airtight jars and sold a sealed product and someone didn't realise they needed to put it in the fridge when it arrived (which does happen), it could explode, so this is not something we can do. We did look into using a chilled delivery option; however, incorporating these costs was just too much to pass on to our customers when purchasing a jar of miso.