One of the ways that plants are distinct from mammals is that plants don’t have nipples. Despite this disadvantage, one can still get milk from a plant.
Generally speaking, what’s called plant milk is a complex beverage made up of extracted plant proteins, fats, and sugars all mixed up into a drinkable package. And while animal milk—such as from a cow, goat, or sheep—is still what most people think of as milk, plant milks are gaining visibility. According to the Good Food Institute, plant milk sales in the US grew 4% from 2020 to 2021 , whereas dairy milk dropped 2%. Overall, plant-based milks slurped up $2.6 billion of US sales in 2021.
A plethora of plant-based milks are available. According to the Good Food Institute, almond milk accounts for 59% of alternative milk sales; oat and soy milk are next in popularity. Other kinds include cashew, hemp, rice, coconut, pea, and milks that are a blend of more than one type. And although there are a variety of types, companies make the dairy-alternative beverages via just two main methods.
But how do you get from green stuff growing in a field to the half-gallon of unsweetened soy in the supermarket cooler? It’s more complicated than getting a three-legged stool and warming up your hands. To make a plant milk, manufacturers need to consider how it feels, how it tastes, and its nutritional value.
At their most basic, plant milks are emulsions: tiny globs of fat and protein swimming in an aqueous sea, more or less evenly dispersed. But making plant milk even look like animal milk requires a scientist’s touch, according to D. Julian McClements, a food scientist specializing in plant-based foods at the University of Massachusetts Amherst. “The light waves have to bounce off it and go into your eye to give it that white creamy appearance of cow milk,” McClements says.
In addition, some plant proteins are almost black when mixed with water, due to the presence of polyphenols. These antioxidant compounds found in plants can also affect the flavor, he says, so milk makers need to remove them. “It looks like a very simple product. But it’s incredibly complicated. There’s a lot of science going into making it look, taste, and feel the way that real milk does.”
There are two basic approaches to making plant milk emulsions, McClements says. “One you can call a top-down approach,” he says, and it works about how most people would guess. “You start off with something like a soybean or coconut, and you grind it up” to extract the fats surrounded by proteins and phospholipids.But the grinding will also create suspended particles of starch granules and protein aggregates. These all have to be of the right size for a good mouthfeel. If the particles are larger than about 50 µm, you can feel the individual particles on your tongue, and the milk feels gritty, McClements says. Smaller particles are creamier, he says. A creamy mouthfeel “depends on the way that fat droplets coat your tongue and lubricate your tongue, the way your tongue goes against your palate at the top of your mouth,” he says.
In comparison, the bottom-up approach means starting off with pure plant oil and proteins and then homogenizing them. This approach takes more energy than the top-down method, according to McClements, and is therefore probably worse for the environment, but it’s much more versatile.
“You can choose exactly what ingredients you want in there; you can make the particles very small or larger; you can use different types of proteins and different types of oils,” McClements says. The bottom-up method can lead to better-quality plant milks with a better mouthfeel, he says, because scientists can control the size of the fat droplets more easily. Another advantage is that manufacturers can easily add nutrients or oil-soluble vitamins during the homogenization process.
Adding nutritional value to plant milks is important because in general plant milks don’t have as many vitamins and minerals as animal milk, a fact that the National Milk Producers Federation (NMPF) has a problem with. In a 2019 comment to the US Food and Drug Administration, the advocacy group, which represents the dairy industry, took issue with plant milks’ being called milk because their nutritional content is not equivalent to that of animal milk.
“Consumers are being misled about the nutritional content of plant-based imitators relative to real dairy products, creating marketplace confusion and inappropriately blurring well-defined standards of identity,” the statement says. For now, buyers in the US can still find the word milk on plant-based beverages in the grocery store. But because of different labeling laws, shoppers in other countries may have to buy “plant drinks” instead.
The protein content of mammal versus plant milk is one of the main differences the NMPF points to. The amount of protein in cow milk varies according to brand and fat percentage but generally falls around 8 g of protein per serving. This outstrips the 2 g of protein per serving of almond milk, the NMPF states, although soy milk generally also has around 8 g of protein per serving. Micronutrients are another point of differentiation. “Milk exceeds the content of almond beverage for riboflavin, vitamin B6, phosphorus, pantothenic acid, niacin and vitamin B12,” the NMPF’s comment to the FDA says.
Until recently, the levels of some niche micronutrients in plant-based milks were unclear. In August, Benjamin Redan of the FDA and colleagues presented research on the nutritional content of eight types of plant-based milk at the American Chemical Society Fall 2022 meeting. (ACS publishes C&EN.)
The researchers found that while cow milk had the highest average amounts of zinc, pea milk had 30% more phosphorus and 80% more selenium than cow milk. Soy milk had 50% more magnesium than cow milk. But on average, plant-based milks were highly variable in their micronutrient levels, Redan said, and people should pay attention to labels when selecting the best type of milk for their needs.
McClements agrees that it’s important to check the nutritional content. People sometimes assume that plant based means better for you, which is not necessarily true. “Looking at some of the products on the shelves, they’re definitely less healthy than cow’s milk,” he says.
But are they milk? That label can’t be thrown around on the basis of nutrition alone, McClements says. “If you made that argument, you couldn’t call strawberry milk or chocolate milk milk because they’re just full of sugar.” But if milk is just something that comes from a mammary gland, then plants are out of luck.