HARIO has been manufacturing and selling heatproof glass since its very inception — and is the only manufacturer with a heatproof glass factory in Japan. In 1948, they began making coffee siphons by taking advantage of the properties of heatproof glass and their refined glass processing techniques. Cold brewed coffee made easy! Place coffee grounds in the strainer, slowly pour cold water into the carafe through the coffee grounds. Refrigerate for approximately 8 hours for the cold brew to complete. Increase steep time for a coffee with more strength.