Robert, I don't know either but I can tell you that simple observation of the container shows that whatever gas was filling the container has gone somewhere and I have to assume it has dissolved into the liquid thereby decreasing the gas pressure and causing the atmosphere to crush the container.??????
Part of the testing is to see if Pepsi type bottles are suitable as many have said. I don't know but will find out if soda bottles work as well as glass. I am not testing those brown photo bottles as I know they don't work as well as glass.