The aroma and color of sake will change when exposed to light. The ultraviolet rays degrade the sake ingredients, causing unpleasant smells and affecting the quality negatively.
So we need to block light in the ultraviolet range (under 400 nanometers) to ensure quality. Both the National Research Institute of Brewing and Gekkeikan's own research institute confirmed that brown glass is ideal for this, so at Gekkeikan we started to use brown colored sake bottles. The item in the photo is a 4-go (720 mL) brown colored sake bottle, and as the label says Brewed under the Supervision of Tsunekichi Okura. We can know that brown bottles were used for sake before 1927, when the company was incorporated as Okura Tsunekichi Shoten, Co., Ltd. There are also records of us selling a special 1-sho (1.8 L) Brown Colored Sake Bottle to commemorate the Emperor Showa's enthronement in 1928.
In the market, however, transparent blueish bottles were still used to hold sake. The full changeover to brown or green bottles to shut out ultraviolet light did not happen until the late 1960s.