a paring knife
a sauce pan
1 liter bottle of vodka
5 rosemary sprigs
5 cups of sugar
5 cups of water
a large vessel with a lid, preferably glass or ceramic, that can hold at least 2 liters of liquid.
(I usually use a large pickle jar; in the photos I'm making a larger batch and using a giant plastic tub).
1 coffee filters (preferably unbleached)
Peel the grapefruits with a peeler. I use about 5 grapefruits per liter of vodka, but you can use more. Save only the peels and discard the fruit (I, of course, eat the fruit right away!).
Sometimes the peels have a a thick strip of the white pith attached to the back. This imparts a very bitter flavor to the final product. If you like bitter flavors, then leave them as is. I don't enjoy that bite, so I fillet the pith from the zesty skin with a small paring knife.
Making Flavored Simple Syrup
Then I make simple syrup by boiling equal amounts of water & sugar together in a saucepan. I add some rosemary to the pot (2 springs per 5 cups of sugar) to give the final product a very rosemary-intense aroma. But, we will be infusing the cello with rosemary later, so adding the rosemary to the simple syrup is optional if you want to keep it simple (no pun intended). When the liquid turns clear (usually this happens just as it reaches a boil), remove the pot from heat and let it cool with the rosemary still in the pot. When cool, strain out the rosemary and discard the spent herbs.
Mixing It Together
Once you have all of this ready, find a large clean vessel with a lid- preferably glass or ceramic- and toss in the peels, the fresh rosemary sprigs, 1 liter of vodka and 1 liter of rosemary infused simple syrup. Save the empty vodka bottle so you can decant the finished product back into the bottle when the infusion is complete. Keep in mind that because of the simple syrup addition you will have about 2 liters of final product to decant back into bottles, so while the cello is infusing try to find another empty vodka bottle in addition to the one you have saved.
Now it is a waiting game. Cover the vessel with a lid, label and date the infusion, put it in a cool, dark place, and forget about it for a while. It will be infused in about 7-10 days, but it can continue to infuse for up to 40 days (and some would argue even longer).
I find that citrus peel vodka infusions are good and ready when the vodka itself changes color. You will notice this after about 12-14 days-- the once clear vodka will take on a dark hue of the color of whatever citrus peel you have used.
Some purists are against filtration (and I feel this way about most wines), however, I do like to filter my vodka infusions. I don't think they look appetizing when they are cloudy or have debris floating in them. Also, if you don't filter, "stuff" accumulates at the bottom and at the meniscus when you store it, and it is a visual turn-off.
I filter these through a good, old-fashioned coffee filter that lines a funnel. I put the funnel into the vodka bottle opening, line it with a coffee filter, and pour away.
Some people believe that cellos should be stored in the freezer and served ice cold. In order for the cello not to freeze in the freezer after the simple syrup dilution the vodka used must be 100+ proof. If you will be storing the product in the freezer, definitely seek out a vodka with a high proof.
I don't think storing these in the freezer is necessary, so I don't do it. I also don't like intense alcohol heat of high proof vodkas, so I don't use a vodka with a super high proof-- I'm going for a more balanced taste. The one I've been using recently is 42 proof, and I keep the final product in the fridge. Some die-hard limoncello drinkers argue that it is "traditional" to store it in the freezer, but limoncello most likely has origins in hot citrus growing climate of Italy, and freezers didn't become a regular household product in Italy until after WWII so storing it in the freezer can't be a very longstanding tradition.
Once you finish you can enjoy this on its own as an aperitif or an after dinner drink. Sometimes I decant them into small bottles and give them as gifts.
It also works great in cocktails. I've mixed it with soda to make a grapefruit rosemary vodka soda. I've added grapefruit juice and made an herbaceous Salty Dog. I've also mixed it with bitter amaro (so many to choose from!) and citrus juice and served it up. The possibilities are endless!
Citrus infusions are great ways to re-use waste, which is one reason I began to make them in the first place. I was juicing lots of citrus and began to think of ways to use the spent citrus shells. Now I make marmalade, infusions such as this one, and I compost the rest.