Thought becomes volatile when tea is taken, less fitted to keep to the facts; indeed, fancy is stimulated by it, very often in a way neither sympathetic to nor in conformity with truth or with sound proportion. Hence one may say that it is comprehensible that in gatherings where flashes of thought and the development of sparkling mentality are in question, the stimulus of tea might be preferred; on the other side, it is also comprehensible that when tea-drinking gets the upper hand, it gives rise to a certain indifference to the demands arising through the healthy structure of the physical earthly body.
So that dreamy fancy and a certain careless, nonchalant nature, a nature that likes to overlook the demands of the sound external life, is awakened by tea-drinking. And in the case of a soul undergoing a theosophical development we feel tea less suitable, as a beverage, than coffee, since it leads more easily to shallowness. The latter tends to soundness, the former more to charlatanry, although this word applied to these things is much too severe.
Source: Rudolf Steiner – GA 145 – Effects of Occult Development: Lecture II – The Hague – March 21, 1913