I cannot find any data on the amount of amygdalin in cherry blossoms.  This is the compound that breaks down in the digestive system into a cyanide substance.  The data I find focuses on amygdalin in the bark, leaves and seeds.  I would think that any levels found in the beer would be low since the blossoms are consumed by the Japanese. I also do not see any disclaimers on the Cherry Blossom Beer stating problems with cyanide levels.  Two things that come to mind would be contact the company that manufactures the beer to see if testing has been done for cyanide.  The other idea would be to have an analysis run on homemade beer made from the flowers of the Cherry tested for levels of cyanide.  Contact a private analytical lab to check on procedures and costs for this type of test.