Hario jug designed for cold brew. Wondering what cold brew is? Cold brew is coffee prepared by soaking ground beans in cold water for several hours. Coffee brewed this way has very delicate flavour, with low bitterness and can be stored for several days. Design The jug is simple, elegant, and made of high-quality materials. It consists of a glass jug, and a steel filter with a lid. Fine filter holds the grounds inside, which results in a clear brew.