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The powerful KegLand Magnetic Stirrer Stir Plate will stir up to 3500 ml in a 5000 ml flask, and is perfect for all yeast culturing needs. It includes a magnetic stir bar. Suitable for Erlenmeyer Flasks from 1000 to 5000 ml.”

Use this in combination with a compatible Erlenmeyer Flask to make a yeast starter.  A stir plate… keeps yeast in constant contact with nutrients, encourages CO2 to off gas and continuously incorporates oxygen all of that means higher cell counts.