Giving homemade liqueurs as gifts is a favourite party trick of mine. They're fun to customise, inexpensive to make, and — if you have a whipping siphon — very easy to throw together at the last minute.
Outside of fancy restaurants and the kitchens of Blumenthal fan boys, nitrous-filled cream chargers are most famous for providing a short-lived "party high." You shouldn't use them for that, but you should use them to make a flavorful, bespoke sipping alcohol in fewer than 20 minutes.
Making a liqueur is a simple process. You simply take a base alcohol with an ABV of at least 40 per cent, infuse it with flavourful root, fruit, or zest (using this method from Gizmodo), then dilute it with an equal amount of syrup to get it into the the ABV range of a liqueur — around 20 per cent.
If you don't have a whipping siphon, the infusion step requires a lot of waiting, but an iSi canister and its chargers makes this a leisurely afternoon project. Here's how to do it:
Add a cup of booze to your siphon. Vodka is a nice, neutral option, but you can use rum, tequila, or anything that strikes your fancy. You can also use grain alcohol, you'll just need to dilute it a little more.
Assemble your flavourings. There are no hard-and-fast rules on how much of what you should add, but I generally use at least a cup of chopped or mashed fruit, or the zest of a whole citrus for every cup of alcohol. For herbs, a sprig or two usually does it, but keep in mind that softer herbs will infuse more quickly that tough, woody ones. For my blueberry Meyer lemon liqueur (pictured above), I used one cup of roughly mashed blueberries and the zest of one Meyer lemon. For my ginger honey liqueur, I used a two-inch piece of ginger, chopped.
Close the siphon, and charge it with one of the whip-its. Wait one minute. Remove that charger, and screw on a new one. Shake the siphon gently for a minute. Depressurize the canister by gently pressing the iSi's trigger. Remove the to lid, let the remaining nitrous escape, and give it a little taste.
If it's not flavorful enough, throw some more stuff in there and repeat steps 2 and 3. Once you have a potent potable, strain out the solids with a sieve then strain out the finer particulates with some cheese cloth.
Now you need to dilute with a syrup. Depending on your flavour profile, this syrup can be made with plain table sugar, turbinado sugar, honey, or agave. For granular sugars, make a syrup using equal parts sugar and water; for the already syrupy sugars, use a ratio of two parts honey or agave to one part water.
Since you are taking the ABV down to 20% (half of our starting ABV) you'll need as much syrup as you have infused alcohol. (So, if you have one cup of infused vodka or whatever, you need a cup of syrup.) Mix the syrup with the liquor, pour it into a pretty bottle, and either give it away as a very thoughtful gift, or keep it for yourself.
The quick nature of these infusions means you can play around with tons of flavours in very short order, creating your own unique liqueurs and tweaking them until they are exactly how you like them. In terms of sugars, keep appearance in mind as well as flavour.
Honey can add depth and temper spiciness, which is why I use it in my ginger liqueur, but it will darken your final product. Some liqueurs — such as the blueberry lemon — are quite pretty and it would be a shame to cover it up with a dark syrup, so stick with plain white sugar for the more vibrant batches. Once you have your liqueur chilled, use it in cocktails, or mix it with some soda water for an easy, fancy adult beverage.