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Plant milks clump in coffee
What milk is made of
Cow's milk holds fat globules coated in phospholipids and proteins, and that structure gives it a creamy look and a creamy mouthfeel. Replicating it from plant ingredients is incredibly difficult, because those ingredients are designed for a completely different purpose in nature.
Plant proteins and fats evolved to store food for a growing plant. They belong to a different family of proteins from milk's, with different surface characteristics, which changes how they interact with the surface of the mouth and the saliva, and that changes how they are perceived.
Trouble in coffee
Tea and coffee are pretty acidic and contain chemicals that interact with the proteins and fats in many plant milks, making them clump up. Baristas also see plant milks fail to foam right, taste of strange off-notes, and turn a strange color in a cappuccino or latte.
Why does acid make plant milk curdle?
Proteins carry electric charge that keeps them apart, and as acidity rises they approach a point where the charge drops to zero and they clump together. For soy protein and for cow's milk casein, that point sits around a pH of 4.5. Coffee has a pH of roughly 5, and heat speeds the clumping. Barista editions often contain buffering salts such as dipotassium phosphate to hold the pH steady.
What do phospholipids do in milk?
Each fat globule in milk is wrapped in a thin skin called the milk fat globule membrane, made of phospholipids and proteins. The membrane keeps the globules from merging and floating to the top as a layer of cream. Homogenization forces milk through a narrow valve at high pressure to break the globules into smaller ones, which makes the milk look and feel even. Plant milks have no equivalent skin.
Why do plant milks separate on standing?
Plant milks are suspensions of tiny solid and oil particles in water, and those particles tend to drift apart on standing. Makers add stabilizers to keep them evenly mixed. Gellan gum, a polysaccharide produced by bacteria, is widely used to hold fortification calcium in suspension.
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