It is most important to avoid all forms of alcohol. Even sweets filled with alcohol have a very harmful effect. Alcohol combined with spiritual exercises leads to the most wrong path. Now that science has proven the bad influence of alcohol on brain function, how much more should a man, who directs his entire efforts to the spiritual, abstain from a delight which completely excludes him from achieving spiritual consciousness.
Source (German): Rudolf Steiner – GA 267 – Seelenübungen 1904-1924 (page 513)