Why you need a fermentation weight Fermentation is a process of producing bacteria. Some bacteria like mold and yeast that can ruin your ferment always grow and thrive in an aerobic environment that has enough air. So one key point for a successful ferment is keep your veggies under the brine and away from the air. A heavy enough fermenting weight can help you create an anaerobic environment, no more worry about mold. *Our weights are made of high quality borosilicate, which can work excellently even with boiling water.