Key limes carry a strong reputation in cocktail circles, but the evidence complicates that story. The America's Test Kitchen comparison from earlier this year is the most rigorous data point available: Persian limes showed lower pH in lab testing, meaning higher acidity, and when used in Key lime bars, the Persian-lime version tasted slightly more tart. Tasters were split on which variety made the better bar. No clear winner.

What Key limes offer is aromatic complexity. TheFlavorExperts describes their flavor profile as more intense and complex than Persian limes, with notes of citrus, green apple, and herbal hints that Persian limes don't replicate. Whether that distinction survives a build that also includes spearmint, sweetener, and soda is genuinely uncertain. No source reviewed here has run a direct side-by-side in a finished mojito. Treat the aromatic difference as real but modest, not decisive.

The practical decision:

• Buy Persian limes if you're making more than two drinks, serving a group, or want a sharper citrus hit. Three Persian limes yield roughly half a cup of juice, per America's Test Kitchen, enough for six to eight mojitos.
• Buy Key limes if you want that herbal, aromatic edge and you're making one or two drinks. Plan on six to seven Key limes per ¾ oz serving. For eight drinks, that's close to 50 small fruits.
• Bottled Key lime juice works as a backup for the flavor without the squeezing. Treat it as a second option, not a first choice.

Neither lime makes or breaks the drink. The technique does.

Before building, three choices matter more than which lime you pick.

Sweetener: use granulated sugar. The granules act as a mild abrasive against mint leaves during muddling, helping release aromatic oils more effectively than a pre-dissolved liquid can. Serious Eats makes this point directly: sugar's physical texture does work that simple syrup bypasses. One teaspoon per drink is the standard. If you want a lower-sugar version, Skinnytaste lists monk fruit sweetener or stevia as interchangeable options, though you'll lose some of the abrasive effect and may need to muddle a touch longer.

Mint: use spearmint. Both Serious Eats and Joyful Healthy Eats specify spearmint, which is also what most grocery stores carry. Peppermint is sharper and more medicinal it will take over the drink.

Carbonation: add it last, stir once. Plain club soda is standard. Flavored sparkling water can work in a mocktail; Joyful Healthy Eats notes you'll want a flavor that pairs well with mint and lime. Whatever you use, it goes in at the end and gets one gentle stir. More than that and you're trading fizz for thoroughness.

Full ingredient list (one cocktail):

• 10 fresh spearmint leaves, plus 2 sprigs for garnish
• ¾ oz fresh lime juice (Key or Persian)
• 1 tsp granulated sugar
• 1½ oz white rum
• Club soda to top
• Ice
• Lime wedge for garnish

Step 1: Muddle the mint with the sugar. Add 10 spearmint leaves and 1 teaspoon of granulated sugar to a tall highball glass. Press and twist gently with a muddler, four or five times. The goal is bruised leaves, fragrant and darkening at the edges, not shredded. Crush them too hard and the flavor turns bitter, per Joyful Healthy Eats; Serious Eats confirms the same light-handed approach.

The common mistake is grinding the mint against the glass bottom rather than pressing and releasing. Use a light hand.

Step 2: Add fresh lime juice. Squeeze ¾ oz of lime juice into the glass. If you're using Key limes, juice them into a small bowl and measure first. Their yield varies enough that squeezing directly in-glass is unreliable. Serious Eats calls for exactly ¾ oz in their standard build.

Step 3: Fill with ice. Pack the glass with ice before adding rum or soda. Cold base, preserved fizz.

Step 4: Add rum. Pour 1½ oz of white rum over the ice. A clean, light white rum is the right call you want it working alongside the lime and mint, not demanding attention. Serious Eats uses white rum in their standard build.

One option: a single dash of Angostura bitters at this stage. Serious Eats calls it untraditional but effective it softens sweetness and adds low-level herbal depth.

Step 5: Top with club soda and stir gently. Add club soda, then give the drink one slow stir from bottom to top to integrate the layers. Serve immediately.

Step 6: Garnish. A mint sprig and a lime wedge on the rim. Press the mint sprig lightly before placing it aroma first, flavor second.

Too bitter: Over-muddling is almost always the cause. The mint releases pleasant aromatic oils quickly; keep going and you're into bitter plant compounds. Next time, use a lighter hand and fewer presses.

Too sweet: Cut the sugar to ½ teaspoon or squeeze in a little extra lime juice to balance.

Too flat: The soda lost carbonation before you drank it. Either the glass sat too long, or it was stirred too vigorously. Build, stir once, serve.

Too tart: Add a small pinch more sugar and stir briefly. Or pull back to ½ oz lime juice next round Key limes in particular can vary in acidity batch to batch.

Weak: ¾ oz lime juice is a fairly light acid load for 1½ oz rum. If the drink tastes thin rather than just mild, the issue is usually mint that didn't release enough oil during muddling. Try muddling slightly more assertively, stopping well before the leaves shred.

Key lime mojito mocktail: Follow the steps above, skip the rum, and scale the sparkling water up to 6.5 oz. Joyful Healthy Eats builds this version with agave and sparkling water at 16 calories per serving. Agave integrates smoothly without needing heat or extended stirring to dissolve, which makes it a cleaner swap than granulated sugar when you're skipping the rum.

Batching for a group: Scale up the lime juice, sugar, mint, and rum. Muddle the mint with sugar in a pitcher rather than individual glasses, then combine everything except the soda. Pour over ice-filled glasses and top each one with club soda at the moment of serving. Joyful Healthy Eats is explicit on this: batches go flat fast if you add soda early.

One practical note on scaling with Key limes: at six to seven Key limes per ¾ oz serving, a round of eight needs close to 50 fruits. Persian limes are the obvious call for any batch larger than two. Three of them yield roughly half a cup of juice, per America's Test Kitchen, enough for six to eight drinks.

Gentle muddling, granulated sugar, spearmint, fresh lime juice, and soda added last. Those are the calls that determine whether this drink is good. The lime variety is secondary.

Use Key limes when they're fresh, you're making one or two drinks, and you want the aromatic edge they bring. Use Persian limes for anything bigger. The America's Test Kitchen data shows Persian limes are more acidic and tasters were split on preference even in a Key lime-specific recipe, so defaulting to Persian isn't a compromise. It's often the cleaner choice.

Mojitos don't hold. Make them, drink them, and if you're serving a group, keep the club soda cold and within reach.