I read it in an anthology from a UK library in the mid to late 1970's but it could have been written much earlier.
Two or three galactic businessmen are sitting in a space bar lamenting about the bartender in there (please note that it could have been a robot but my memory fails) because the bartender can make this unique and wonderful cocktail.
All efforts to copy this fail because certain tiny drops of some alien juice are added during the mixing process, however the mixer does a kind of shuffle as he's adding these drops and doesn't know exactly how much he adds. If he tries to slow the procedure down to analyse it then it comes out wrong and doesn't taste very nice.
The cocktails don't keep so they can't be exported, within a few minutes they go bad and sour so you have to drink them as they're made ....I think they also have to be shook at certain times during the mixing as various alcohols are added so chemical analysis won't help.
Eventually they manage to use some super high speed camera (digital?) and can finally reproduce the drink by carefully programmed robots