Why heat a cocktail? Heating booze can caramelize sugars and burn off some of the alcohol vapor. Hot cocktails are also one of the most delicious ways to heat up on a cold winter’s day. With National Hot Toddy Day coming up on January 11, we wanted to focus on the science behind this drink—and other classic hot cocktails—to keep you warm.

Old Flames

Toddies have been around since the early 17th century. Back then, alcohol was used as a preservative for many medicinal tinctures, as well as being considered a medicine in and of itself. Every part of the toddy served a purpose: citrus for vitamin C, sweetener for taste, spices for perceived holistic reasons, and booze to numb painful symptoms.

Back then, it was concocted from whatever was locally available, which has left a large number of traditional recipes behind. But to ignore the flip, another traditional hot tipple, would be to leave wide gaps in cocktail history. (For today, we’re leaving out hot punches, Tom and Jerrys, and Irish Coffee for the sake of length.)

Back in colonial days, a flip was made with beer or cider, sugar, and liquor. To warm it, a fire-heated poker was plunged into the drink, triggering the Leidenfrost effect (when a protective vapor shields a liquid from boiling after the immersion of a heat source). At first, the drink doesn’t bubble, but after a few seconds, it begins to do so violently. Heat from the poker caramelizes the sugar in the drink, leaving a rich, caramel, toasty flavor profile.

Heat Sources

If your kitchen (or favorite neighborhood tavern) is ill-equipped to heat pokers, there are other ways to heat your beverage. The two most common are to add hot liquid (usually water) or to heat the mixture in a saucepan. Each of these has unique advantages and disadvantages.

With water, you don’t get any of the caramelization effects, and much less of the alcohol vapor is burned off. Since alcohol boils at a lower temperature than water (173° Fahrenheit vs. 212° Fahrenheit), a small percentage of the alcohol will evaporate. Heat intensifies the smell of alcohol, so adding hot water may make it smell boozier than it actually is.

If you’re willing to play with fire a little, you can mimic the effects of a hot poker with a saucepan. First, caramelize the sugar in the pan. Add the base liquor for the drink, and set it on fire. To make sure that it’s kept in check, quickly add the nonalcoholic ingredients and remove the pan from the heat source. The first two steps will create the same type of taste profile as the poker drinks. The third and fourth will ensure that it’s not too burnt to drink.

It’s Hot, Sticky Sweet

Heat messes with our perception of sugars. The hotter the drink, the more intense sucrose becomes, meaning that table sugar seems a whole lot sweeter. Fructose, on the other hand, is less noticeable when it’s heated. So, if you want to use honey or agave, don’t be afraid to add a bit more.

Hit the Lab

Though the toddy’s exact origins are unknown, it’s still a great way to end a cold day. Note: if you’re using hot water or tea, consider serving the finished beverage in a wide-mouthed vessel. Using a cylindrical coffee mug funnels the alcohol vapors into your face while you’re drinking, which can intensify the smell.

Hot Toddy

1/2 oz lemon juice
1/2 oz honey
2 oz bourbon

Combine all ingredients in a wide-mouthed cup or mug. Add hot water to taste and garnish with a lemon wheel or cinnamon stick.