Protecting your HomeBrew Sake from light

Sake, as with other beers, is sensitive to light and in particular ultraviolet light. Sunlight is the greatest offender having a much higher degree of ultraviolet light than most other sources. This is not to say that other sources are harmless, they can have a negative impact as well. Given that sake can be harmed by this light and light is all around us, what can we do to keep our sake safe from this harm?

We can choose to use bottles that have the best properties for filtering the light and specifically the ultraviolet light. Fortunately for us, Bradley E. Sturgeon, PhD¹ recently did a study that examined which colors of glass bottles provide the best light filtering.

Visible light runs from about 400nm to 700nm in wave length with the shorter wave lengths being of higher energy. Ultraviolet light is in the range of about 280nm to 380nm, just below that of visible light. These high energy waves damage sake by damaging the amino acids and vitamins in sake causing it to turn yellowish or more yellowish and develop an off putting aroma.

Based on Bradley’s data displayed in the chart below which covers most of the ultraviolet range, blue glass stops (absorbs) only a little more than 70% at 325nm and then drops down to less than 20% for 350nm and 400nm. Green glass does a little better but neither blue nor green come close to the effectiveness of brown glass. Brown glass stops 96% or better over this range.

A second way to look at this data is to look at the intensity of the light that gets through the filter (not absorbed). The chart below shows this data along with the intensity of the light from the sun unfiltered. As you can see in this chart a blue bottle has very little effect. Green does a little better. But brown stops almost all the light at these wave lengths. In fact, brown seems to do the best for all light sources up to about 500nm.

Given all the above the best color bottle to use to store your homebrew sake is brown.