Starbucks' $1.25 cold foam is the chain's most popular drinks add-on, and one of its most expensive. This is how it's made.

• Cold foam is now Starbucks' most popular beverage modification.
• It's made by frothing nonfat cold milk and is added to iced drinks like cold brews.

Customers can't get enough of Starbucks' cold foam. It's now the coffee chain's most popular add-on, and it's pushing up the Siren's revenues.

The "velvety" foam is made by frothing nonfat cold milk "until it is smooth, creating layers of creamy texture and flavor without the cream," Starbucks says.

A recipe for sweet-vanilla cold foam on Starbucks' website says that customers can make it at home by frothing cold milk with powdered sugar and vanilla extract. For a one-person serving, it suggests using a quarter-cup of 2% milk, a tablespoon of powdered sugar, and a quarter of a teaspoon of vanilla extract. A New York Times recipe recommends using heaving whipping cream, too.

"The ideal cold foam is both fluffy and pourable; it seeps gradually into your preferred coffee drink or iced beverage over time," according to an article by Epicurious. "It adds a sumptuous, creamy texture to any beverage, and often doubles as a vehicle for sweeteners and flavorings."

The cold foam can be served on top of cold coffees that already have milk in them, or can add a splash of dairy to a black iced coffee. Epicurious notes that though you can use substitute the milk with non-dairy milk, whole milk, or heavy cream, skim milk works best.

Starbucks first debuted cold foam when it opened its Reserve Roastery in Seattle in December 2014, but the foam wasn't introduced to its regular coffee stores until April 2018.

While some drinks come with cold foam on top as standard, such as some of its flavored cold brews, customers can opt to add it to other cold drinks for $1.25. The price stays the same regardless of whether you order Starbucks' biggest drink size, at 30 fluid ounces, or smallest, at 12 fluid ounces.

It's more expensive than the chain's other customizations, including adding a flavored drizzle, sprinkles, chai, syrup, or extra shot of espresso. The only modification that appears to cost the same amount as adding cold foam is substituting the milk with vanilla sweet cream.

Currently there are six flavors of cold foam available – chocolate cream, cinnamon sweet cream, matcha cream, salted caramel cream, vanilla sweet cream, and white chocolate macadamia cream.

The foam has been a massive success for the coffee company. It's featured in a number of customized beverages that have gone viral on TikTok, including iced white mochas with vanilla sweet cream cold foam and extra caramel drizzle, perhaps because it provides an attractive layered appearance. It was also included in the Pink Drink Remixed, based on a viral beverage.

Starbucks has even rolled out handheld cold foam blenders to all its US company-operated stores so that baristas can make it more quickly.

Starbucks isn't the only place you can get cold foam on your drink. Tim Hortons in the US, for example, sells set chilled drinks with cold foam and also has the option for customers to add it to some of its other cold drinks.

Dunkin' started selling sweet cold foam in February 2021, and has since launched it in a number of time-limited flavors including brown sugar and salted caramel. "We're starting to explore more layered drinks that offer unique, textural experiences for our guests, and think Sweet Cold Foam unlocks an exciting opportunity for continued innovation in the Cold Brew category," Olivia Vaughn, the company's associate research and development technologist, said in a press release at the time.

Heinz Kraft brand Maxwell House has launched make-at-home iced lattes with foam, its first new product in nearly a decade. Even Aldi has sold cold foam in squirtable cans.