This is a pretty nerdy one, so here’s the tldr:

Bartenders need ice like chefs need ovens. There’s 3 things that really matter to get your drinks right:

Down a back street in Islington is the Canal museum, a truly excellent day out for families and nerds. The museum is built in a Victorian ice storage facility, and you can still see the ice wells that were used there. The ice was bought by boat from Norway and, incredibly, mostly survived all the way to the drinkers of London (and the butchers, fishmongers and doctors). Margate’s fantastic antiques warehouse, Scotts, is also built in an old ice warehouse, so clearly there was a huge demand for ice.

(yes I stole this from the daily mail, saved you a click, etc)

But how does ice survive a long trip from Norway to London, where it can be stored undergound for months without melting? The answer lies in the science of what happens when ice melts. The cooling of your drink, or side of beef, isn’t just bought about by the fact that the ice is cold, but a much more significant factor is that the actual melting of ice takes energy from its surroundings, chilling them much more than would happen if the only factor was the temperature of the ice (in other words, an endothermic reaction). This is why we can make ice cream with salted ice water: even if the ice is at zero degrees when it’s added to the salt water, the process of it melting will bring the solution to well under freezing for the ice cream maker.

When it comes to making cocktails, we’re looking for two outcomes from using ice. 

In order to get both of these right, we need to really consider our ice cubes.

Cocktail bar ice cubes will generally come from a Hoshizaki machine (other brands exist, but these are what most decent bars choose). The ice is an almost perfect cube with a tiny dimple in the base and it is, for want of a less pretentious term, limpid. The ice is dispensed into an insulated box where it sits, ready for making drinks, at a perfect 0 degrees. That’s great, because it means we’re starting with a known quantity: the only chilling we’re getting is from the ice melting, and the only dilution we get is from the melted ice. If the ice is standing in water, we’ll get too much dilution to start, and if it’s straight form the freezer at -20 the drink will be too cool for the ice to start effectively diluting it when we do reach 0 degrees.

On top of that, we have to bear in mind our surface area to volume ratios. The reason Esme, my adorable runt of a dog, can run around so much in the heat is that her surface area is quite high compared to her puny volume, but a much larger dog has to lie in the shade as it simply can’t get rid of the heat it generates in its volume through it’s comparatively low surface area. 

Our ice works the same way: crushed ice has the highest surface area to volume ratio, and melts really fast, chilling and diluting our drink at a reckless rate that tends to be offset with creamy drinks; we can serve a frozen pina colada because the density of the drink stands up to a lot of dilution, but many other drinks would be ruined by crushed ice. Cracked ice is the next step, and it’s great for stirred drinks where we’re in a rush to get the drink chilled and diluted, but will be straining it off the ice when we’re done. For shaken drinks, we can use the ice cubes, because the violence of shaking breaks off lots of edges and corners, giving us a bonus for chilling and dilution, but we then to strain it onto fresh cubed ice to arrest that process as much as possible.

After they’ve made the drink, you’ll mostly see bartenders use fresh ice to serve it. One of my favourite bars, Happiness Forgets, uses ice straight from the freezer at this point, which is really the perfect solution: it will keep the drink cold, but gives you a few minutes longer before the dilution starts up again. We also want to use as much ice as possible when we serve it: a couple of lonely cubes will just dilute your drink without substantially cooling it, while a column of cubes all the way up the glass will keep it chilly and undiluted for longer.

For negronis, old fashioneds and spirits on the rocks you’ll often see massive cubes or spheres of ice. These stretch the surface area to volume game even further, and mean your drink can sit for 10-20 minutes without significantly diluting.

If you want good, clear ice at home (the clearer ice is, the slower it will melt), the secret is directional freezing; forget what you’ve read about filtering or boiling the water, this is the only technique that really works. Fill some sort of insulated vessel, like a cooler or thermos flask with ice (if you use a flask, it will need to have a neck as wide as the rest of the chamber) and, leaving the lid off, put it in your freezer. It will take much longer to freeze than normal ice cubes, so come back in a few days, take it out and leave for an hour or so for the ice to slightly melt around the edge, allowing you to slide it out of the cooler/flask. You’ll see that the very bottom is extremely cloudy, but the vast majority of the block is perfectly clear. Chip off the cloudy bit and you can break up the rest for use in your cocktails.

Now you’ve got some lovely clear ice you can use it to make a mojito, the Cuban (ish) way. You’ll need: