I've made a lot of liqueurs and infusions over the years, and limoncello was the one that got me started. For the most part, I've always used one of the more traditional methods, wherein the zest of the lemons is steeped in alcohol for at least 10 days, then strained and sweetened.
However, there are some tricks to extract more flavor and to complete the liqueur in less time—as in hours.
The act of steeping the peels in vodka works because vodka is basically just water and alcohol, both of which are solvents for the flavor compounds in the rind. Most of the flavor is in the aromatic oils in the zest, which would be dissolved by the alcohol. To speed things along, you can use a method to extract the oils more quickly and make them more available.
This involves muddling the rinds with sugar. Through osmosis, the granules of the sugar break down the cellular structure of the rinds, releasing the oils. This is called oleo saccharum, or "oily sugar," and it's a common tactic among bartenders to get a more potent citrus flavor. I learned this technique from "Shrubs: An Old-Fashioned Drink for Modern Times" by Michael Dietsch.
The other thing that speeds the process along is elevating the temperature of the solution. By packing the liqueur in a vacuum-sealed bag and immersing it in a heated bath in a method called sous vide, you are allowing the compounds to dissolve more rapidly.
Because the bag is sealed, you retain all the aromatic compounds and alcoholic content of the liqueur. Using this recipe, you can create a limoncello in just three hours, as opposed to the traditional method, which takes 10 days or longer.
If you do not have a sous vide immersion circulator, you can simply complete this recipe by steeping as you would the traditional recipe. It will take longer than 2 hours, but likely less than 10 days. It should be ready as soon as the sugar is dissolved.
- 6-7 lemons
- 1 cup sugar (granulated)
- 2 cups vodka
- 1 cup water
- If using sous vide to make your liqueur, set the circulator to 135ºF/57ºC.
- Use a vegetable peeler to cut away strips of the lemon zest, being careful to only take the outermost, yellow part of the rind. If the backside of the strips has much of the white pith, use a sharp knife to carefully shave it away, and discard it.
- Combine the lemon peels with the sugar, and gently crush them together with a wooden spoon or muddler, until all the rinds have been bruised and have good contact with the sugar. Cover, and let stand at least one hour.
- After an hour, the sugar should have extracted the oil from the rinds; they will look dewy and glistening, and the sugar will have a texture like wet sand. This is the oleo saccharum.
- Combine the oleo saccharum (rinds and sugar together) in a quart-size vacuum-sealer bag. Squeeze out as much air as possible, and seal the bag. Immerse the bag in the water bath for 2 hours. Remove to an ice water bath to cool.
- Alternatively, combine the oleo saccharum in a quart-size mason jar with the water and vodka. Cover, and shake to distribute the sugar. Steep, shaking at least once a day, until the sugar is dissolved and it reaches the desired flavor.
- Strain out the peels, and decant into a bottle. Store in the refrigerator.