It wasn't that long ago that bartenders would reach for a suspect-looking bottle of store-bought lemon juice or sour mix any time a cocktail calling for citrus was ordered. The recent cocktail renaissance has brought back a much-needed appreciation for fresh juices.

But to really capture the complex flavors of lemons, limes, oranges, and grapefruits, you have to think beyond just juice. Today, we look at some sweet suggestions for getting the most out of these sour fruits.

1. Fresh is not always best

Cocktail guru Dave Arnold first reported that lime juice that had been sitting for 4 hours tasted better to a panel of blind taste-testers than fresh lime juice.

We still don't have a bulletproof scientific explanation for why this happens, but quite a few people have demonstrated similar results.

I've tested the phenomenon myself and came to these conclusions:*

Orange juice: fresh is, in fact, best. An unpleasant bitterness develops just 30 minutes after juicing.

fresh is, in fact, best. An unpleasant bitterness develops just 30 minutes after juicing. Lime and Lemon juice: aged for 4 to 10 hours is best. Juice aged four hours did seem to taste more mellow while the top notes seemed to pop a little more. After 10 hours of storage, the juices seemed to lose some of their aroma, and after a day of storage bitterness became noticeable and unpleasant.

aged for 4 to 10 hours is best. Juice aged four hours did seem to taste more mellow while the top notes seemed to pop a little more. After 10 hours of storage, the juices seemed to lose some of their aroma, and after a day of storage bitterness became noticeable and unpleasant. Grapefruit juice: aged for 1 to 3 days is best. Juice held for a day was noticeably more bitter, but that actually made the juice taste more grapefruit-ey. After three days, the juice tasted like it had lost much of its aroma, though the bitterness still wasn't overpowering.

Here's what I think is going on.** What's behind both the increased bitterness in juice and the improved taste in aged juice is the bitter chemical limonin. There's almost no limonin in fresh-squeezed lemon and lime juices, but some precursor chemicals of limonin are present. When fresh juice is exposed to air, enzymes convert those precursors into bitter limonin, a process known as enzymatic bittering.

Why would bitterness make juice taste better? In very small amounts, bitterness has a suppressive effect on the other basic tastes.*** In 4-hour-old juice, I think the bitterness is suppressing some of the intense acidity in lemon and lime juices, which allows the drinker to perceive more of the subtle nuances of the juice's flavor.

Is it worth it to intentionally age juice for a tiny improvement in quality? I would argue probably not. The real takeaway from these observations is that if you do have to do some of your juice-prep work a few hours in advance of a party, your cocktail quality won't suffer (with the one exception of orange juice.)

*I stored my juices in a small mason jar at refrigerator temperature after juicing. I had my roommate serve me the juices in random order so the test was blind, but the conclusions were subjective to my palate. Give it a try and see what's true for you. **Harold McGee cites oxidation as the culprit, but Arielle Johnson's gas chromatograph analysis of 4 to 20-hour-old lime juice showed very little oxidation. She did find that volatile aromatics as a whole in the juice decreased, and this can change the perception of quality, but it isn't yet clear how. I've also tested pH (it doesn't change significantly over the times we're concerned about). So of all the known possibilities, the effect of increasing bitterness seems to be most important. For more on the science, see here. ***This may be one reason why a dash or two of bitters helps to "round out" a drink. I've written a bit more about the science here.

2. Store citrus in the refrigerator, prep it in the microwave

Citrus fruits will keep for a few days at room temperature, but will be good for several weeks in the fridge. Just make sure you don't try to store a fruit that you've peeled or zested. The oil-filled peel of a citrus fruit acts as a moisture barrier that prevents the insides from drying out.

Unfortunately, cold citrus doesn't release its juice as easily. This is due to two factors. First, the juice-containing vesicles in a citrus fruit are made of the complex carbohydrates pectin and cellulose. These carbohydrates are strong in colder temperatures and so are less likely to release the juice. Second, all citrus juices contain sugar, which means the viscosity (thickness) of the juice also increases as temperature decreases.* That's why it helps to toss the fruits into the microwave for 15 or 20 seconds just before juicing. You want to get the fruit just barely warm, not hot.

What about the tip about rolling lemons around on the table before juicing? It doesn't actually do much; plus, you lose some of the oils from the lemon peel, which, as we'll discuss, are extremely important not to lose.

*For more science on this topic, see Chapter 7 of this book—though most of the takeaways can be seen in this paper by the same authors.

3. Lemon and lime juice are not interchangeable.

Lemon and lime juice both have a pH* of around 2, which makes them relatively strong acids. But, pH is only one component of the perception of sourness. The overall concentration of acid (known as titratable acidity) also changes sourness. Plus, sweetness will significantly mask the perception of sourness.

Take a look at the below chart to see just how different citrus juices can be.

Note that a lime will yield about between from 0.5 and 1.5 ounces of juice, while a lemon yields between 1 and 2.5 ounces. Since yields can vary so significantly, always buy more citrus than you think you'll need and make sure to measure your juice for recipes.

If you try substituting lime juice for lemon juice in a cocktail, you might find that the balance is slightly off. As you see in the ratio chart above, the lime is as acidic as lemon (even a little more so), but it has less sugar. So substituting one citrus fruit for another might mean you have to add a little acid or sugar to re-balance the drink.

*pH is a measure of the acid content in a solution. The scale runs from 0 to 14. Lower is more acidic. Water sits at neutral, pH 7.

4. Twists: Get their oils out!

This one might seem like a no-brainer, but it's worth mentioning since most of us have seen it done wrong at some point or another. First, make sure you check out Michael Dietsch's excellent guide and follow up on using citrus garnishes in cocktails. In these articles, Michael demonstrates the difference between thick "rustic swaths" of peel and "dainty spirals".

Whatever type of twist you choose to make, make sure to actually twist the darn thing. When you twist a lemon peel, the oils stored in oil sacs found in the fruits epidermis (yes, it's really called that) rupture and those oils flavor your cocktail.

Take a closer look at the acidity chart above. The acidity and sugar levels for lemons and limes are pretty similar, so how do we so easily tell them apart? By their aroma—the vast majority of which is stored in the skin of the fruit, not in its juice.

If you are making a fancy twist with a channel knife, note that many of the oils in the peel will be released when you actually cut the twist with a channel knife. To capture more flavor, cut the twist directly over the serving glass whenever possible.

Upping Aroma

Many bartenders like to rub a lemon peel along the outside of the cocktail glass before service, but I'm not a fan of this technique. I find that the initial hit of aroma is too intense. Instead, I think it's better to rub the twist along the inside of the glass before pouring the cocktail in so that the oils release slowly, in layers. Compare it to "rinsing" a glass with absinthe before pouring a Sazerac into it.

Toss it in or leave it out? There are two sides to this argument:

Leave it out: the epidermis of citrus fruits, where delicious oils are stored, also happens to be the same place where dust, wax, pesticides, and fertilizer gather. Do you really want any of that in your drink? Plus, the bitter compounds found in any pith attached to the twist will slowly leech out and infect the flavor.

the epidermis of citrus fruits, where delicious oils are stored, also happens to be the same place where dust, wax, pesticides, and fertilizer gather. Do you really want any of that in your drink? Plus, the bitter compounds found in any pith attached to the twist will slowly leech out and infect the flavor. Toss it in: you can avoid all the above problems by carefully washing your fruit in warm water just prior to service. Since ethanol is a non-polar solvent, a small amount of citrus oils will dissolve into alcohol itself while the rest will slowly float to the top as you drink the cocktail, resulting in a layered release of flavor.

you can avoid all the above problems by carefully washing your fruit in warm water just prior to service. Since ethanol is a non-polar solvent, a small amount of citrus oils will dissolve into alcohol itself while the rest will slowly float to the top as you drink the cocktail, resulting in a layered release of flavor. Sometimes, it's required. Some drinks, like the Horse's Neck, call for the peel from an entire lemon. When this much peel is involved, the way the peel slowly releases layers of flavor as you make your way through a drink is a critical part of the experience.

My personal verdict: As long as you properly clean your twists, feel free to drop them in.

5. For faster drinks, use an atomizer

At home, I don't usually like to peel a lemon every time I need a lemon twist unless I need lemon juice as well. The very outside layer of the peels of citrus fruits is epicuticular wax—a complex mix of hydrocarbons that prevent moisture loss from the rest of the fruit. Cut off even a tiny section of this protective skin, and the rest of fruit will dry up in a hurry.

So instead, I simply pour a bottle of lemon extract into an atomizer and pump a spritz over the top of my drink.

Aren't extracts full of foul chemicals?

For something to be called an extract, the flavor component of the product has be derived from the actual original food product. Consider lemon extract. The fruits are peeled en masse at a factory that produces lemon juice and the peels are then either allowed to sit in a solvent (like alcohol) or heated until their oils naturally release. The oils are then spun in a centrifuge and checked for purity using a gas chromatograph before they are bottled and added to ethanol and sold as lemon extract.

That's not to say all extracts are of equal quality. The industry gets paid big bucks to add tiny amounts of terpenes, esters, aldehydes, and the like (all naturally occurring in citrus peels) to tweak the flavor profiles of their extract.

If a flavoring is made from something other than the original food it's supposed to represent, the product will be labeled "flavoring," "artificial," or "imitation". To read the law yourself click here. If you're still not convinced, you can always make your own lemon extract by simply steeping lemon zest in high-proof alcohol.

Of course, no amount of science beats a real taste test. In my experience, commercial lemon extract doesn't quite match up to a real lemon peel, but it's worth it for the convenience value.

Here's the real power of this technique: lemon peels have been shown to heighten the perception of sweetness. And so has vanilla. Using an atomizer with extract—whether homemade or store-bought—gives you the ability to add a wallop of flavor with just a tiny spritz. Maybe toss a few black peppercorns and some dried bitter orange peels into the bottle if you want to get even more complex.

6. Or use frozen juice

I get this question a lot. Is it ok to freeze citrus juice? And the short answer is: yes, but don't expect it to be the same as freshly-squeezed.

We've already discussed how all citrus juices change immediately after squeezing. Enzymes in the juice activate and slowly produce limonin, a bitter compound that eventually makes the juice taste pretty, well, bitter.

Unfortunately, freezing citrus juice will not deactivate the enzymes that cause bitterness, but it will slow down their activity significantly.

I would recommend against freezing orange juice because it's unlikely the juice will fully freeze within the 30 minutes before bitterness becomes noticeable. But lemon, lime, and grapefruit juices should hold well in the freezer. Freeze these juices in 1-ounce ice cube trays for easy use later on.

One reminder: if you do freeze juice, its likely to lose some volatile aromas to sublimation.* To refresh the juice before using it, simply add the juice of a fresh fruit for each ice tray full of frozen juice and squeeze the oils out of the peel into the juice. This is also a great trick for bolstering bottled juices if that's all you have access to.

*The conversion of a liquid directly into a gas, without passing through the liquid phase. This happens in very cold and dry environments, like a freezer.

7. Or pre-make infused citrus syrup

In bartending circles, a lemon-peel-infused simple syrup is known as an Oleo Saccharum. These syrups were originally used in punches as a base of flavor. Michael Dietsch has written about oleo saccharum before here on Serious Eats..

Although most folks recommend muddling lemon peels to express their oils, innovative bartender Jeffrey Morgenthaler discovered that the muddling step is actually unnecessary.

Here's why I think is Jeff's technique works. It's similar to what happens when you salt a steak. When an imbalance of sugar between inside and outside of the lemon peels exists, some water gets pulled from the peels via osmosis. As water leaves, many of the fruit's cells rupture, which then releases oils into the mix. Although oil isn't directly soluble in sucrose, the syrup ends up thick enough that the oil stays dispersed within.

Although Jeff recommends vacuum-sealing lemon peels and super-fine sugar in a vacuum bag, I've tested the technique, and neither super-fine sugar nor vacuum sealing are necessary. To make an intense lemon syrup, simply toss lemon peels into a zip-top bag, lightly coat with granulated sugar, and let the mix rest at room temperature.

The best thing about this technique? It works with all kinds of fruits and vegetables. My current favorite? Ginger.

8. Citrus flavors don't only come from citrus

Whenever we talk about the top tier (this is Serious Drinks, after all) of fine beverages like coffee, tea, or wine, measures of quality are based on complexity and how flavors play off each other. The same can be said about cocktails. If citrus is the flavor, how can you add dimension to the basic top notes provided by a citrus peel?

I first came across the idea of using citrus analogs to boost citrus flavor when I read Dushan Zaric's recipe for lime cordial (which you can use instead of Rose's Lime). He calls for 4 cups of lime juice, 2.5 cups light agave nectar, and 40 leaves of kaffir lime leaf—and no lime peel whatsoever. The syrup is intense and aromatic and brings a welcome angle to drinks like the classic Gimlet.

You have many options for making syrups that bring complementary flavors to citrusy drinks. For lemon, the obvious starting point is lemongrass, which is available both dried and fresh in many supermarkets. Some less obvious choices include common spices like cumin, coriander, and green cardamom. Leave them untoasted and use simmered whole spices if possible. Dried tamarind also adds a sour, orange-y taste.

Why am I telling you to use cardamom as a lemon substitute? Consider that one of the key flavor compounds found in oak-aged spirits is vanillin, the critical flavor component of vanilla. Last time I checked, vanilla beans don't grow in oak barrels. When wood is toasted, some of the complex carbohydrates that give it its structure (cellulose, hemicellulose and lignin) break down and become, among flavors, vanillin.

The key citrus flavors are limonene and citronellal, and they appear in many of the spices I mentioned above. Just as caramel and smoke seem to go naturally with vanilla, some of the spices you probably already have in your kitchen can pair surprisingly well with citrus. For more ideas, be sure to check out The Flavor Bible: The Essential Book to Culinary Creativity and for a more high-tech approach, the interactive flavor exploration site Food Pairing.

Bonus: Citrus is just one way to add acid to a drink

While orange, lemon, lime, and grapefruit are offer great flavors and acidity, why limit yourself?

Here are a few other ideas for adding acid to cocktails:

Pineapple. This tropical fruit contains more acid and less sugar than an orange. While its juice has long been a pillar of tiki culture, what other services could it provide?

This tropical fruit contains more acid and less sugar than an orange. While its juice has long been a pillar of tiki culture, what other services could it provide? Apple. While apples are significantly less acidic than citrus fruits, some varieties are actually very tart. There's also more malic acid in apples than citric acid, which changes the tang these fruits impart. If straight apple juice or cider isn't sour enough for you, consider using apple cider vinegar. On that note...

While apples are significantly less acidic than citrus fruits, some varieties are actually very tart. There's also more malic acid in apples than citric acid, which changes the tang these fruits impart. If straight apple juice or cider isn't sour enough for you, consider using apple cider vinegar. On that note... Shrubs. This breed of drinking vinegar has gained well-deserved attention in recent years. Vinegars are shelf stable and offer up flavors not found in any other liquid. If you're ever in New York, make sure to stop by the Filling Station in Chelsea Market to for free sample of amazing gourmet vinegars. For DIY types, I recommend grabbing copies of Ideas in Food and The Art of Fermentation, books that embrace both science and deliciousness. And don't miss Serious Eats' own excellent guide to making DIY Shrubs.

This breed of drinking vinegar has gained well-deserved attention in recent years. Vinegars are shelf stable and offer up flavors not found in any other liquid. If you're ever in New York, make sure to stop by the Filling Station in Chelsea Market to for free sample of amazing gourmet vinegars. For DIY types, I recommend grabbing copies of Ideas in Food and The Art of Fermentation, books that embrace both science and deliciousness. And don't miss Serious Eats' own excellent guide to making DIY Shrubs. Kombucha. Wnd with a pH of around 3.0, kombucha can provide a powerful wallop of sourness.

Wnd with a pH of around 3.0, kombucha can provide a powerful wallop of sourness. The straight sour. Remember sour patch kids and that crazy sour stuff they were coated in? That was mixture of sugar and straight citric acid. One of the nice side effects of the 'molecular' or 'modernist' food movement is that some pretty interesting acids are now available for about five bucks. Add a little pinch of citric acid to a drink and you can up its acidity without otherwise affecting flavor.

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