The San Francisco temporary bar TSK/TSK, which will sometime this year be reincarnated as Horsefeather, featured several alcoholic slushies on its menu.
Slushmaster Mitchell Lagneaux said he was often asked for his advice on how to make them delicious, and rather than writing the same advice over and over he thought he'd point them to this post on Alcademics instead.
So here goes. The below is all courtesy of Mitchell Lagneaux.
There are a few ways one can go about making adult slushies for the masses. You can fill the machine with Slushie mixers, add a bit of booze, or a lot of booze, flip a switch, and an hour later its game on. Nothing wrong with this approach but sometimes you want to achieve a frosty, brain freezing booze bomb with more of a fresh taste, or maybe there isn't a mixer that fits the occasion. I don't know, pick your excuse to not use a margarita mix. Here's a guideline to help you achieve the coolest of cool, the coldest of cold, sweet yet refreshing, adult slushie.
First, if you are looking to serve slushies in a bar or for an event, you want to consider the portion sizes of the beverage. This is going to help you later on with tracking cost. Lets say you want to serve a slushie at 10 ounces. There will probably be at least 2 ounces of liquor in the cocktail. In order to freeze up you are going to need to add quite a bit of water. Think about how much ice you put into a blender when making a frozen drink. You should be filling the blender with ice if you want to get that heavy frozen consistency. So I recommend adding twice the water to booze when assembling your ice palace.
So already we have 2oz booze + 4oz water= 6oz total liquid.
Now it's time to think about the modifiers. Lemon, lime, pineapple, coconut? Sugar, honey, crazy house made syrup? You probably already have the drink in mind that you want to make though. The thing is, the drink is not going to come out tasting the same once frozen as when it's shaken or stirred. The drink is going to taste thin and diluted. So we need to beef up our mixers. Lets take, for example, a Daiquiri.
Some might make a non-slushie Daiquiri like so:
.5oz simple syrup.
But when making a Daiquiri that's going to be colder that a witch's teat, we need to add a bit more sugar to the mix. Adjusted, our Daiquiri might look as such:
1oz simple syrup.
If you're like me you are going to want to test the drink out before letting the world taste you masterpiece. I've heard of some people weighing ice, or letting a cup of ice melt and seeing how much water it's made up of. The most simple way I can tell how to test out what your frozen beverage is like this.
Make a modified Daiquiri (2oz rum, 1oz lime, 1oz simple). Build this bad boy in a shaker, fill it with as much ice as you can, shake it till the wheels come off, and when you strain the cocktail, measure it. What do you have? Let's say 7oz.
7oz total - 2oz rum - 1.5oz lime - 1oz simple syrup = 2.5 water (dilution)
Lets add another 1.5oz of water to get the drink to the level of water required to freeze. That's brings us to 8.5oz per cocktail. And there you have the serving size. It should taste bit sweet but once frozen the drink should balance itself out. If you feel like it's too sweet or sour make the adjustments as needed.
Now that we have a basic formula for making our slushie we need to have some batched and ready for when it gets low.
Spending time abroad made me appreciate the metric system. Let just remove the "oz" from our recipe and replace it with "mL" and it's that easy.
The last, and one of the most important things in my opinion when it comes to serving slushies is the time at which you refill the machine. It typically takes at least an hour for a full machine to freeze the liquid. With that being said, the lower you let the batch go before you add more, the longer it's going to take to get cold.
I recommend topping up the machine when it's about half way down. A trick I've learned is to roll, or rack it once you fill it. This means pour in more of your batch. Next, take the same container you used to fill the machine, fill it back up with the slushie you just topped, and do this 3 or 4 times. This is going to get all of the liquid in the machine to the same temperature, resulting in a faster freeze. Otherwise the new batch will sink to the bottom and the frozen portion will float at the top.
Brain freezes for all!