Breathable foam stoppers will withstand boiling or autoclaving temperatures, making them ideal for use in preparing a yeast starter. The honeycomb structure of the foam stoppers will act is a filter for any airborne bacteria or wild yeast that might enter the flask. That important because a lot of air is sucked into the flask while it is cooling. You can also leave the stoppers on the flask instead of a fermentation lock. Some people use foam stoppers to replace fermentation locks in their carboys, too.

The small foam stoppers are 35-45mm wide and fit our 500 or 1000 ml borosilicate glass flasks, or a glass carboy.

California Proposition 65

Proposition 65 Warning: This product contains chemicals known to the State of California to cause cancer and/or birth defects or other reproductive harm.