There are many types of dairy alternatives on the market today, often made from things like nuts and soybeans. But have you heard they're now making butter from air? A US startup called Savor is working on a range of dairy alternatives made using something that exists all around us: carbon. Fats are made from chains of carbon, hydrogen and oxygen atoms. Savor's process involves taking carbon — from, say, carbon dioxide — and adding heat and hydrogen to create chains that are combined with oxygen from air. This results in fat molecules, like the ones found in dairy and other animal products. Now, regular butter is about 80% fat — the rest is mostly water. So to make butter from its synthetic fat, Savor just adds water, as well as an emulsifier that keeps the liquids from separating, and rosemary oil for flavor and beta carotene for color. What does it taste like? "I couldn't believe I wasn't eating real butter," Microsoft co-founder Bill Gates wrote in a blog post earlier this year. Gates is one of Savor's investors. He wrote that "it tastes really good — like the real thing, because chemically it is." Savor has already run informal taste tests with small groups of people, and is working to get regulatory approval for its product in the US. But why butter? A 2021 study estimated that food production makes up about 35% of the world's greenhouse gas emissions — and Savor estimates that about 7% of greenhouse gas emissions are just from producing fat. But Savor's process, Gates wrote, doesn't release any greenhouse gases. He added that it uses no farmland and "less than a thousandth of the water that traditional agriculture does." Savor is focusing on butter to start with partly because its high price point makes it easier to compete on cost. But the startup later hopes to develop other products like milk, ice cream, cheese — even meat.