Large coffee chains and neighborhood espresso bars make much of their profit from steamer drinks, beverages that combine a small quantity of espresso coffee with a lot of steamed and frothed milk. If you can't drink milk, or would prefer a vegetarian option, coconut milk is one of the most steamer-friendly alternatives. It handles the heat beautifully and brings a rich and pleasant flavor to your steamed beverages.
Milking a Coconut
Like smaller nuts, coconuts are rich in fats, proteins and other nutrients. If you shred the flesh of a coconut and steep it in hot water for 15 to 20 minutes, the water dissolves and absorbs the coconut's flavors and nutrients. If you pour the soaked coconut into a colander lined with cheesecloth and squeeze every possible drop from the coconut pulp, it produces rich and creamy-textured coconut milk. Like whole milk, it has a fattier "cream" component, which rises to the top if the milk is allowed to rest. Stir your fresh-made coconut milk, or shake your canned coconut milk, to recombine the lean and fatty portions for beverages.
Thickening With Foam
There are several ways to thicken milk or coconut milk, but they all involve partially immobilizing its water content. For example, the egg proteins in custards or the starch molecules in starch-thickened puddings bond together to form a sort of invisible 3-D sponge that holds water in place. Foams work by tying up liquid in the form of tiny bubbles, which use surface tension to keep a miniscule portion of the liquid in place. If you have lots of fine bubbles, you can create a stable, long-lasting foam that holds its shape when it's spooned onto the top of your coffee. Heating the milk makes a more stable, long-lasting foam.
Boiling or steaming changes the proteins in either dairy milk or coconut milk, causing the molecules to unwind from their normal tightly balled shape. These fine strands of protein drift into one another as the milk is heated, forming long chains of proteins. These make stronger bonds in the coconut milk, increasing the amount of surface tension it can generate. This means the individual bubbles in the foam are stronger and are better able to resist the expansion of the hot air inside. The result is a longer-lasting, more substantial foam.
Making Your Drink
If you have an espresso machine with a steamer wand, you can foam coconut milk just as you would dairy milk. Otherwise, bring the coconut milk to a low boil in your microwave or a saucepan on the stove top. You can whisk the coconut milk to an acceptable foam if you're patient or use an electric beater or milk frother. Alternatively, microwave the coconut milk in a sealable canning jar. Once it's hot, cover the jar tightly and shake it for a few minutes. It will foam generously, providing a mixture of hot coconut milk and fluffy foam to make up your steamer drink.