Now the name of a frozen dessert, the word sherbet appeared in English in the seventeenth century, meaning “a cold fruit drink,” and developed two spellings reflecting its two pronunciations, sherbet (SHUHR-bit) and sherbert (SHUHR-buhrt). Today both spellings and both pronunciations are regularly encountered in both British and American use, to the discomfort of some purists, who argue that only sherbet is acceptable.
Meantime, food fanciers have reborrowed this word in its French form, sorbet, pronounced both in the French way (sor-BAI) and an anglicized (SOR-bet). Standard English now uses all three forms, although Edited English usually clings to sherbet and continues to italicize the French sorbet as foreign.
Australian English now uses sherbert, both alone and in compounds, as another name for beer.
From The Columbia Guide to Standard American English at http://www.bartleby.com/68/37/5437.html