Flavours include peppermint, cinnamon, spearmint, wintergreen and two sour flavours, cherry and apple. The three most common flavorants are peppermint, spearmint, and wintergreen. Cadbury-Adams also manufactures "Certs Powerful Mints", available in peppermint, spearmint and wintergreen. Bark on twigs rich in methyl salicylate (oil of wintergreen). Circa early 2011, Altoids altered the ingredients of their Wintergreen mints, adding blue food colouring. The most common flavors consist of mint, wintergreen, straight, and natural. The taste is comparable to Wintergreen Tic Tacs. Oil of wintergreen can be distilled from the bark. The remaining flavors, Straight, Mint, Wintergreen, Natural, and Southern Blend, fall into a sub-premium level. While usually due to aspirin, other possible causes include oil of wintergreen and bismuth subsalicylate. The roots often have a scent reminiscent of wintergreen. Twinflower, strawberries, bunchberries, horsetails and wintergreen form an attractive grown cover. Many fragrances, e.g. oil of wintergreen, are in fact antifeedants. Small amounts of oil of wintergreen can be toxic. William Randolph Wintergreen grew up in Oxford, England.