5000 ml Borosilicate glass flask is perfect for making very large starters for high-gravity beers and lagers. Borosilicate glass tolerates rapid changes in temperature, making these flasks ideal for preparing yeast starters. Just boil your wort in the flask to sanitize the foam stopper. Place the flask directly on a gas stove, then move it to an ice bath to chill! Not recommended for use with electric stove elements! Takes a #11.5 stopper to seal.