What could be simpler than simple syrup? Grab some sugar, add water, put it on the stove, and—stop. You've already gone to more trouble than you need to. Here's why.
Ready for the forehead slap?
You don't have to heat simple syrup. The science is simple, really. Sucrose (granulated sugar) dissolves just fine in water at room temperature. How much sucrose? About 2000g/L, or just enough to make a thick 2:1 simple syrup by mass.
Granted, the sugar takes some time to dissolve. If you're making a 1:1 syrup, you can simply combine equal parts sugar and water and it'll do its thing in about 15 to 20 minutes.
But, for a 2:1 syrup, you'll probably need closer to 45 minutes, with a good shake or stir at the halfway point.
45 minutes seem like a long time? Sure, it's faster to form a syrup on the stovetop or microwave, but don't forget that you'll need to wait for that heated syrup to cool. Plus, the nonheated method requires less active time and fewer dishes to clean up.
Benefits to not heating simple syrup
Ever since I started making syrup this way, I've noticed a few other benefits. First off, unheated syrup seems to be very slightly more viscous (thicker) than heated syrup. According to cocktail writer and chemist Darcy O'Neil, this is due to the breakdown of sucrose into simpler fructose and glucose molecules when it is heated. And as you may remember from my post on gomme syrup, a thicker mouthfeel is usually a good thing in cocktails.
Here's the other, more important benefit: you get to avoid cooking off delicate aromatics.
For example, if I wanted make a syrup with from a base of fresh-squeezed orange juice, I could simply add sugar and not worry about cooking off the juice's delicate scents and flavors.
Fresh herbs and delicate spices also do better without heat. You can also combine techniques, say by macerating grapefruit peels, then adding grapefruit juice at room temperature to form a syrup.
One reason you still might want to cook a syrup
Of course, any technique has its downsides. Here's the biggest issue with not heating simple syrups.
When you cook a simple syrup, the heat kills some of the bacteria and other microbes naturally occurring in the syrup. Add the syrup to a mason jar before it cools and the hot liquid will kill microbes in the jar as well.
The dangers of microbial spoilage varies from place to place. Some people claim to be able to keep a rich 2:1 syrup on the shelf indefinitely, but mine goes bad in about 3 months, even refrigerated. If you're already having issues with syrup spoiling before you can use it all, using the cold process method may not be for you.
It may not be worth it to you to make cold-infused syrup if you're already struggling with the shelf life of your simple syrups. But, this trick may come in handy for those times when you need a quick syrup and don't want to heat up the stove, or when you're trying to avoid cooking off delicate flavors.
Another reason to cook a syrup
Here's how I make grenadine, a traditional pomegranate syrup, at home: pour a cup of POM pomegranate juice into a Pyrex measuring cup and let it go in the microwave until there's only half a cup left.
I love the caramelized, earthy notes that come from cooking the pomegranate syrup at high heat. Heck, I love the taste of caramelized syrup in general.
So if you're using heat as a means to build flavor, then by all means go for it. But if you're trying to keep aromatic flavors from cooking off, consider keeping things cool.
What's your favorite homemade syrup? Have you ever tried using a cold-infusion method?
About the author: Kevin Liu likes to drink science and study cocktails. Wait, that's backward. Ask him geeky food and booze questions on twitter @kevinkliu. While you're at it, check out his book about cocktail science and his blog about food and science