I’ve been making simple syrups for homemade beverages for over a decade now, and I’ve since created tons of variations of them. This key lime simple syrup recipe is bright and zesty while also being sweet and tart. Key limes are much less acidic and tart than regular limes available at the grocery store, making them the perfect candidate for this simple syrup! It’s made by using both the juice and the zest of fruit, so it’s full of fresh lime flavor!
This syrup was inspired by a large crop of key limes from the tree in my parent’s backyard. I planted the tree in the early 2000’s, and it’s churned out pounds and pounds of key limes since then. When you get that many limes, you have to use them or you lose them! Since making this lemon simple syrup, I knew key limes had to be my next citrus syrup. This is the perfect simple syrup for a variety of tropical and tiki drinks, from a classic Cuban daiquiri to a key lime margarita!Jump to Recipe
💕 why you'll love this key lime simple syrup recipe
🍋 bold & zesty. Key limes are tart, but not as tart as regular Persian limes, which are the most common variety available at the grocery store. They have a sweet, almost unique floral flavor to them!
🍭 sweet & tangy. Sweet and floral key limes make this simple syrup stand out from other lime simple syrups. It’s delicate but tangy in flavor, making it perfect for using in all your cocktails and mocktails!
🏝️ flavorful & tropical. Key limes are famous for desserts and tropical destinations. By making this simple syrup, you can infuse that tropical flavor into any beverage you like with ease! Key lime pie sodas anyone?!
- key limes - This recipe is best made with fresh key limes if you can find them. You’ll need a whole bag, because they are much smaller than traditional limes. Not to quote Ina, but fresh really is best. 😇 If you can’t find fresh limes, you can also make this syrup using a high quality bottled key lime juice. Try to find ones that use only fresh juice, not from concentrate, and with no added sweeteners.
- granulated sugar - regular granulated sugar is perfect for simple syrups. It ensures your syrup will be light in color, and have a very pure, sweet taste without hints of nuttiness or caramel. However you can definitely swap out the sugar for your favorite sweetener of choice. Avoid using artificial sweeteners, though, as they can change the sweetness level and consistency of this recipe.
- filtered water - filtered water works best for simple syrups since the water will not be cooking at a rolling boil. Using filtered water keeps the flavor profile pure and clean, without any funky flavors.
Step 1: Zest 6-8 key limes, enough to get about 2 tablespoon of lime zest. Juice 1 pound of limes to get 1 cup of juice.
Step 2: Add 1 cup of water to a small saucepan and place it over medium heat.
Step 3: Add in 1 cup of granulated sugar, and stir until it dissolves.
Step 4: Pour in the key lime juice, and turn the heat to medium-low, allowing it to reach a low-simmer for up to 15-20 minutes.
Step 5: Turn the heat off and add in the key lime zest. Allow the mixture to steep for up to an hour to infuse the intense flavor of the zest.
Step 6: Allow the syrup to cool completely. You'll notice the zest will have lost its vivid color--that's totally normal!
Step 7: Strain the mix through a fine mesh sieve to remove the zest.
Step 8: Store your finished simple syrup in an airtight container, and store in the fridge for up to two weeks. You can also freeze it for longer storage!
Hint: While it might be tempting to skip the step of zesting your citrus and just throw in the whole juiced lime halves, resist the urge to do so. The pith of the citrus, or the white fleshy part, tends to impart a strong and bitter flavor. By only using the zest, you get the bright flavor without a bitter aftertaste.
🍽️ serving tips
Simple syrups are best used as a liquid sweetener in beverages because they are so thin in consistency. They don’t work as well for topping desserts like ice cream or on breakfast foods like waffles and pancakes. You can still use a simple syrup on food, but just be aware that it will be thin and may soak into porous foods quickly.
Usually, if you’re looking for key lime drinks, it’s hard to find anything that’s not a dessert inspired cocktail. But by swapping out the simple syrup in classic cocktails for this key lime simple syrup, you can move past the sugary sweet beverages in a rimmed martini glass. 😛 It works especially well in rum, tequila, and vodka-based drinks! Of course, you can make a key lime martini, or key lime pie martini, but here are some more ideas for your syrup!
- classic key lime daiquiri - classic daiquiris are shaken in a cocktail shaker, not blended with ice. Try taking a look at this classic cuban daiquiri for inspiration, and add in this key lime simple syrup instead of sugar for an extra zesty twist! If you do want to make a frosty frozen beverage with this, try it out in a key lime colada!
- key lime margarita - a classic lime margarita is always a great choice, but by adding in a bit of this simple syrup in place of agave in your recipe, you’ll get an added burst of floral lime flavor!
- key lime mule - lime and ginger beer are a match made in heaven. Try using this key lime simple syrup in your mule recipes to add a touch of sweetness and zing!
You can also use this simple syrup to sweeten non-alcoholic beverages and mocktails! I love using it in homemade soda recipes— it’s the perfect treat on hot summer days!
- limeade - use this key lime simple syrup instead of sugar and swap lemon juice for lime juice in any lemonade recipe to make key lime limeade!
- homemade key lime soda pop - make your own homemade sodas by adding 1-2 ounces of key lime simple syrup to sparkling water or seltzer water.
- key lime iced tea - add this syrup to your favorite iced tea for a subtle hint of lime flavor.
Cooking & Baking
- keep baked goods moist - use this simple syrup to brush layer cakes and keep them moist between layers! This key lime syrup would pair nicely with citrus cake or vanilla cake! It would be absolutely wonderful on berry cakes, too!
- homemade shave ice topping - this syrup works very well as a homemade shave ice topping!
ℹ️ troubleshooting tips
- Juicing the limes- Key limes are quite small, so it takes a lot of them to get 1 cup of juice. On average, one pound of key limes will yield 16 ounces of juice. Allow your limes to come to room temperature before juicing to get the most juice out of them.
- Tart or acidic limes - It can be difficult to gauge how sour or bitter citrus will be just by looking at it. I always recommend tasting your citrus juices to get a good idea of how much sugar you’ll need to use to balance things out.
- Adding sugar - Typically, key limes are sweeter than regular limes, or Persian limes, so you won’t need a ton of sugar to balance things out. But if you grabbed a bag of key limes that are more sour, you will need to up the amount of sugar you use to make sure that your final syrup isn’t overly acidic. Add sugar 2 tablespoon at a time until it reaches the sweetness level you like!
Make sure to taste your syrup as you go! The acidity of limes varies greatly, so you may want to add more sugar if it's too tart.
Add more sugar 2 tablespoon at a time until your syrup gets to your desired sweetness level.
⚖️ Scaling Tips
It is super easy to scale up simple syrups! You can make a double batch and freeze some for later, or you can gift it to family and friends.
🔆 top tip
Check out this post here for tips on successfully freezing your simple syrups. They don’t always freeze solid, depending on the final sugar content and acidity. Since this syrup is both sugary and acidic, it may not freeze completely solid.
Missing an ingredient? No problem. Check out these tried-and-true substitutions, or comment below with your question. I’m here to help you troubleshoot!
- bottled key lime juice - if you can’t find fresh key lime juice, you can use a bottled juice in this recipe. Make sure to use a high-quality juice that is 100% key lime juice with no added ingredients like sweeteners. For a bonus, look for one that is not from concentrate. This key lime juice from King Arthur Baking is a high quality bottled juice that works well in this recipe!
- regular limes - you can use regular lime juice in a pinch with similar results. Depending on the limes you use, you may want to add more sugar. This is because Persian limes, which are the most common limes in grocery stores, tend to be more acidic than key limes.
- sugar - if you don’t have regular granulated sugar, you can use another type of sugar like sugar in the raw or brown sugar. If your sugar is darker, it will affect both the color and flavor of your final syrup, so keep that in mind!
Feeling like a rebel?! 😈 Feel free to stray from the recipe card using these variations, or leave me a comment with your own!
- lemon - check out my recipe for lemon simple syrup here if you only have lemons instead of limes! You can also make a lemon-lime simple syrup by doing a half and half mixture of lemons and limes!
- ginger - add in fresh ginger for a lime and ginger simple syrup that’ll knock your socks off! It’s perfect in cocktails and mocktails like a mule and a dark and stormy!
- other spices - other spices like cinnamon, cloves, and allspice partner beautifully with limes!
🧰 equipment needed
- heavy-bottomed non-reactive saucepan - you can use whatever saucepan you have on hand, I love this 1.5-quart saucepan from All-Clad. The heavy bottom ensures even heating throughout the cooking time! A non-reactive pan is a pan that is made from a metal that doesn’t react to acidic substances, like stainless steel or enameled cast iron.
- non-reactive mesh strainer - a fine mesh strainer helps you to separate the lime pulp and zest from the liquid after simmering the mixture. Make sure to use a fine-mesh strainer that is made of stainless steel, or use a nylon straining bag for this recipe.
- airtight storage - you can use any airtight container you like. These OXO squeeze bottles are a favorite of mine for storing simple syrups because you can also stash them in the freezer. These glass bottles are great for gifting simple syrups to friends and family. You can also use a mason jar!
- measuring cups - if you don’t have a kitchen scale, you’ll likely need some measuring cups. I love this Anchor Hocking glass measuring cup set because they can tolerate the quick temperature changes that happen when I’m making simple syrups. I also love this set of measuring cups from King Arthur Baking because they are sturdy, nest well, and include any size you’ll ever need!
- kitchen scale - using a kitchen scale has so many benefits, from being more precise to helping you do less dishes! If you use a scale, you can simply put everything right in the pot as you measure it, no need to dirty up a bunch of extra dishes! I have and love this OXO kitchen scale.
🛠️ The right tools for the job:
- Use pots, pans, and strainers that are non-reactive, like stainless steel. Additionally, I recommend using silicone utensils instead of wooden or metal tools. Enameled cast iron is also a great choice!
- Aluminum can react to acids and impart a metallic taste, even when you’re just quickly straining a liquid! Wood can also absorb flavors from cooking, whereas silicone tools can be left right in the pot when things cook. It’s important to not use aluminum if you can help it for this homemade syrup recipe, because lime juice is acidic and could lead the aluminum to impart a metallic taste to your finished syrup.
- The best bet for a pure lime flavor is using non-reactive tools, like stainless steel, enameled cast iron, and silicone.
You can’t store this syrup at room temperature for longer than a few hours because it uses fresh, perishable ingredients. Store your simple syrup in the fridge for up to two weeks. You can also freeze it for longer storage.
I love storing syrups in these OXO squeeze bottles for easy measuring in recipes. These glass bottles with stoppers from Bormioli Rocco are excellent for gifting, too!
Key limes are less acidic than regular limes, which are traditionally Persian limes. They are also slightly sweeter and have an almost floral-like flavor to them. Their rind is much thinner, and they are also much smaller in size. A fully grown key lime is a bit smaller than a ping-pong ball!
You can use bottled key lime juice if you can’t find it fresh. Check your local grocery store’s produce section, or try talking to your store manager to request key limes. Key limes are in season from June through September when they are grown in Florida. Some varieties, like those grown in Mexico, are available year-round.
Key limes got their popular name from the times when they were grown in the Florida Keys. However, due to environmental factors, the amount of commercially grown limes from Florida has dwindled. You can still find Florida-grown limes, but for the most part, they are no longer grown in large supply in the Florida Keys. Most of the commercially grown key limes in today’s markets are grown in Mexico.
📌 pin this recipe for later!
If you make this recipe, please leave a review in the comments and a star rating!
I read every single comment! I also love connecting on social media, so snap a pic and hashtag it #myrecipeforfun and tag me on Instagram, TikTok, or pin this recipe on Pinterest!
Key Lime Simple Syrup
- 1 1-pound bag key limes enough to get 1 cup of juice
- 300 grams sugar 1.5 cups
- grams filtered water ½ cup
- Wash and dry the key limes before juicing them.
- Zest 6 of the key limes carefully using a microplane.
- Slice and juice approximately 20 key limes to get 240 grams of juice (1 cup).
- Add 118 grams of water (½ cup) to a small saucepan and place it over medium heat.
- Add 300 grams of sugar (1 cup) and stir it until it dissolves.
- Once the sugar is dissolved, add in the key lime juice.
- Allow the pan to come to a low simmer over medium heat for 15-20 minutes.
- Turn off the heat and allow the mixture to cool for at least 30 minutes.
- Strain the simple sryup through a fine mesh strainer to remove the zest.
- Store your finished simple syrup in an airtight container in the fridge for up to 2 weeks, or freeze for up to 3 months.
🧯food safety & other information
Food safety is an important ingredient in any recipe for success! Here are some tips to keep you safe in the kitchen!
- While you can allow this syrup to sit at room temperature, don’t leave it out for longer than 4 hours at a time. This helps to inhibit bacteria growth that can happen from the sugars in the syrup. Read more about the temperature danger zone here.
- Use sterilized containers whenever possible. You can sterilize your containers by boiling them briefly, running them through your dishwasher with the sterilize feature activated, or pouring boiling water into the containers.
- While you may be able to use your simple syrup longer than 2 weeks in the fridge, if you see any sort of cloudiness or dark spots in the syrup, throw it out. This is mold growth and is not a recipe for fun.
- Never leave simmering syrup unattended on the stove.