Light and high temperatures spoil the quality of sake, hence bottling it in brown or green bottles to avoid the effect of ultraviolet rays. The amino acids and vitamins that are plentiful in sake degrade on exposure to light, causing the sake to discolour and to acquire an unpleasant aroma and bitter taste. High temperatures hasten chemical reactions between sake ingredients. The changes caused by high temperature vary depending on the type of sake, but in general there is deterioration in aroma and taste compared to sake that is allowed to age in low temperature. The ideal temperature for storing sake is around 15 degrees Celsius, the same as for wine cellars. Since there is almost no use of cork in the sake bottles, humidity is not an issue. Once opened, a sake bottle should be sealed and stored in a refrigerator to retard oxidation.