With the Boston snow accumulation looking to soon surpass Shaq level, it's hard to picture these wintry months as a good season for citrus. Nevertheless, tis true even (thanks in no small part to globalization) in Boston. A trip to a good grocer or market right now can yield you a number of exciting finds including blood oranges, Meyer lemons, and Seville oranges (at least for a bit longer). That being the case, it seemed an appropriate time to begin a series I've been plotting to do a for a while now, an exploration of what I've learned about citrus and its use in various mixed drinks and libations.
Let's start with the common players. The most common citrus you will find when dealing with the realm of cocktails and other libations are lemons, limes, oranges, and grapefruits. So far, not very controversial. It's worth noting, however, that without writing a treatise on the topic, there's a number of less common varieties that make for some interesting drink components. One is the aforementioned blood orange, which is most available in the winter season. The juice is not worlds different from common sweet or naval oranges (a really good blood orange will have a hint of raspberry taste), but I for one prefer it, having acquired a taste for it when drinking fresh squeezed OJ in Italy during the winter months some years ago. Also, if nothing else it adds a fantastic color to a drink. Perhaps the best application I've seen for them is the Blood Orange - Jalapano Margarita (courtesy of Cocktail Hacker).
Seville oranges (aka bitter oranges) are another interesting subset. These oranges are bitter, some (or most) would say unpalatably so for eating or drinking the juice from. However, they are great for instances where bitterness is exactly what you are seeking, for example when making cocktail bitters or as an interesting substitute for a tart lemon. Vin d' Orange, a French liqueur made with white wine and spirits combined with sweetener and Seville oranges is another application (Nightcapped has a recipe here; the Nov./Dec. issue of Imbibe! Magazine also has one). Bergamot oranges are another rare variety with similar properties and uses (see the Adventures in Cocktails blog's post about them here). Bergamots are, among other things, noteworthy as a main ingredient in Earl Gray tea (further information can be found here and here).
On the other side of the spectrum, there are Meyer lemons, which are in taste a hybrid between a lemon and an orange (depending on how ripe they are, the color also runs the spectrum from yellow to the color associated with oranges, i.e., well, orange). According to Jeffrey Steingarten, Meyer lemons are named for Frank N. Meyer, who discovered them in 1908 in Peking (apparently they are might be a hybrid between a lemon and a Mandarin orange, but it's not known for sure). Imbibe Magazine's Jan/Feb. issue includes a feature with cocktail suggestions that use Meyer lemons specifically (as discussed further below, I like them for Limoncello as well).
A final note: if you are looking for Seville oranges, from my experience you need to hit up a very good market; I have not seen them at Whole Foods or other larger brand stores (in the Boston area, Formaggio Kitchen in Cambridge has some). Seville oranges also have a notoriously short season; they are usually available only in the January/February timeframe. Meyer lemons and blood oranges are easier; I have seen them in Shaws, Trader Joe's, and Whole Foods to name a few (though not always; it's hit or miss, and obviously only when in season).
So, now that you've got your citrus in hand, fancy or common, let's get to know the anatomy a bit. For our purposes, the relevant, non-scientific divisions can be described as zest (the outer skin of the fruit), pith (the white, spongy material beneath the skin), flesh (the soft, juicy center), juice and seeds (excepting of course in the seedless varieties). Once again, this is unlikely to be a great revelation. Where things start to get interesting, however, is the fact that these different elements can serve a variety of different ends, and additionally, the parts that will be of most interest will vary depending on which type of citrus you are dealing with (and, of course, what mixological purpose you have in mind).
The main value of zest is that it is the source of flavorful, aromatic oils. It is these oils that are in fact generally the most flavorful part of the fruit (not the juice). Thus, when you see a citrus twist as a garnish in a drink, it's often more than just purely decorative. In particular, the classic technique for applying a citrus garnish to a drink is to rub the skin side of the cut peel around the edges of the glass, and twist the peel over the drink, ringing out some more oils into the drink itself (the classic approach is usually to then place the peel inside the drink itself rather than just adorn the side). A more advanced use of a citrus garnish that highlights these oils is the flamed garnish, typically done with orange or lemon peel, whereby the peel is twisted or squeezed next to a flaming match such that the oils are ignited as they shoot off of the peel and into the drink. The oils aren't necessarily enough to dramatically change the flavor profile of the drink (the quantity is, after all, relatively trivial). However, flavor is so concentrated in these oils that even in these small quantities that come off the garnish, they can produce a significant aroma that influences the taste of the drink itself, sometimes significantly.
Garnishes are far from the only use of precious citrus oils. One additional use is the creation of flavored tinctures, which can themselves be used as components or additives for drinks. Creating a tincture basically just requires steeping some citrus peel or zest in high proof alcohol, usually of the most flavorless variety available (basically, high proof grain alcohol if available or vodka), and then straining the contents. The alcohol extracts the flavor from the oils, giving you a concentrated flavoring agent. These tinctures can then be uses as components of liqueurs, cocktail bitters, and other such concoctions (see, for example, Jamie Boudreau's recipe for a homemade Amer Picon substitute).
Still another way to utilize citrus oils is to use a different means of extraction, sugar. Dave Wondrich has an excellent discussion of this extraction of the "ambrosial essence" that is citrus oils into oleo-saccharum ("oil-sugar") in his book Punch: The Delights and Dangers of the Flowing Bowl (2010). There, he describes this oleo-saccharum as one of the Pillars of classic punch (of the 17th-19th Century, pre-cocktail era variety). Essentially, this extraction consists of rubbing the sugar against cut citrus peel by muddling the two together (or, in the earliest techniques, rubbing what amounted to a brick of sugar against the skin of the citrus, essentially sanding it off; unfortunately, this isn't really viable with the modern forms of sugar you get, according to Wondrich's experimentation). Not just for punch, however, this technique should also be familiar to anyone that has ever made or ordered an Old Fashioned, the archetype on which the cocktail itself was based, or anything that borrows from the same idea.
Next, as a sidestep from the tincture use and oleo-saccharum described above, we have the use of zest in liqueurs. Liqueurs are comprised of base spirits to which flavoring agents (fruits, for example) and sweetener (sugar) is added. The quintessential example in the current context: Limoncello! The Italian liqueur Limoncello is generally fashioned by steeping lemon zest/peel in neutral grain spirits for a time, adding simple syrup (or sugar, and later water if you prefer), aging and straining. [That being said getting the authentic Italian result outside of Italy is a challenge - the lemons just aren't the same. I visited the Naples area once and saw some Sorrento lemons sold by the street, along with some delicious granita made with them; they were easily the size of grapefruits! I have yet to see their like anywhere in the states. For the record, I tend to use Meyer lemons when I make Limoncello. I have no empirical evidence myself, but I have read that the result comes closer to the result you get with the Italian fare.]
Now, before moving on, a quick note on the separation of zest. I have not focused on technique in this post, only because I intend to include that in a subsequent post on this topic, but the main thing to know about getting the best out of the peel/zest is to avoid pith. While the outer skin of the fruit contains flavorful oils, the pith is unpalatably bitter. The rule of thumb is to cut away and discard as much as possible when attempting any of the uses described above. As a further side note, some applications of citrus peel/zest call for dried peel (usually dried orange peel). Recipes for cocktail bitters, vermouth, and even beer use dried citrus peel as ingredients. For bitters at least (and often times these other applications as well), it's usually Seville, or bitter orange peel you are looking for unless called for otherwise. I've heard it suggested that for whatever reason, when recipes for these items call for dried peel, fresh peel does not get you the proper result. Fortunately, whether you dry your own, or purchase some from a local spice store or beer brewing supplier, dried citrus peel is generally not hard to come by.
As noted above, some types of citrus lend themselves to certain applications more than others. As a general rule, it's usually lemons and oranges that are used for zest-related applications (again, generally speaking). The reason is that when dealing with lime or grapefruit, the concentrated flavoring is considered a bit too sour on its own, enough so that it ruins the balance of the drink. That said, you will still see those types of zest if combined with juice, or the peel from other types of citrus (or both), which tempers the flavor. As an example, take the Mojito, where, depending on which technique you use, you may be muddling lime slices with bruised mint leaves and sugar. In that situation, you get some flavor from the oils of the lime zest, but it's tempered by the mint oils and juice from the lime. It's worth noting here that Seville orange zest can make an interesting substitute for lemon zest; however, common or sweet orange zest, however, will be much different (much milder).
The next key element is of course juice. The sky is the limit when it comes to using citrus juice. It can be an ingredient in Punch, a cocktail, or even a liqueur. Also, it can sometimes be found on its own as an ingredient or combined with peel/zest as well (Wondrich notes that for Punch, you tend to see both used if dealing with cold punch, and peel/zest only if dealing with hot Punch). Lemon juice and lime juice are probably the more prominent in the cocktail and mixed drink scene. Many pre-prohibition era cocktails in particular use lemon juice as an element (although lime is found as well). Punches favor lemon as well. For the tiki line of drinks, however, lime is without a doubt king, having a prominent place in the majority of drinks in the genre. Orange juice is probably the next most commonly used, with an occasional appearance in vintage cocktails like the Monkey Gland (Wondrich has an entire section on Orange Punches as well). Grapefruit juice is probably the least common of the four, but irreplaceable when called for. I would wager the most well-known drink that uses it is the Salty Dog, comprised of vodka or gin, grapefruit juice, and salt.
Finally, there's one other major way in which citrus finds use in cocktails and other libations: marmalade. Citrus fruit marmalade is in short made by taking chopped up citrus fruit (especially the peel and juice) with sugar (and pectin), and cooking. Some techniques call for discarding the pith and/or the seeds. (David Lebovitz has some recipes here and here). In addition to something great to spread on toast, this also provides you with an interesting cocktail ingredient. The Savoy Cocktail Book, for example, has a recipe for the Marmalade Cocktail that utilizes orange marmalade, lemon juice, gin, and simple syrup (via Underhill-Lounge). Jaimie Boudreau also has a recipe for a Marmalade Sour that utilizes orange, grapefruit, or other citrus marmalade. While a trendy cocktail ingredient in recent years, Paul Clarke notes that marmalade has actually been used as a cocktail ingredient at least as far back as the 1930s (via Serious Eats).
Thus ends my introduction to the wonders of citrus in the cocktailian world. More to come soon!