Mo. Rev. Stat. § 311.100: Sale by drink defined.

The sale of any intoxicating liquor except malt liquor, in the original package, in any quantity less than fifty milliliters shall be deemed "sale by the drink" , and may be made only by a holder of a retail liquor dealer's license and when so made, the container in every case shall be emptied and the contents thereof served as other intoxicating liquors sold by the drink are served.