Mint is vital to a whole range of cocktails, from the Mojito upwards (or downwards depending on your point of view), yet has always proved a problem to keep fresh, especially for a long service. It is quite a delicate herb, and traditional solutions like covering it with a wet cloth or putting the stems in a glass of water have their own problems.
The problem seems to start as soon as you strip the bottom leaves off a sprig and cut the stem short. The enzymes in the plant start to degrade and the mint starts to go brown.
We looked at ways of arresting this process, or at least of slowing it down. Freezing was an obvious choice, but this would be impractical as drinks require fresh, not frozen mint. But this did lead us to look at what actually happened to the mint when it was frozen. It slows down the the enzymes working and the mint going limp or brown.
It was obvious that freezing stopped the degradation process, and stopped the mint going brown. So we wondered if we could use a part of that process ie to flash freeze or like a reverse blanching.
So we cut the stems to length with a sharp knife and plucked all leaves apart from the top ones. We placed the cut stems and leaves in very cold shallow water (with crushed ice) and covered them with more ice for five minutes only. This seemed to seal the mint leaves, almost cold searing them, (as the common misconception that you hot sear a steak to keep the juice in): the flavour is kept in, and the only disadvantage is that the mint loses just a shade of its colour although if get the timing right, you keep this to an absolute minimum.
After that, all we needed to do was place the ends of the stems standing up in a container with shallow water and store them in the fridge until needed. But the mint looked spritely all night long.