Cell Based Milk
The basics

How cell-based milk is made, step by step

Cell-based milk relies on a trick mammary cells already know: take in nutrients on one side, release milk on the other.

Updated 4 min readBy the Cell Based Milk team
Illustration of mammary cells on a membrane releasing a drop of milk

Key takeaways

  • Mammary cells are grown in a nutrient broth, then arranged so they can absorb nutrients on one side and release milk on the other.
  • Unlike cultivated meat, the cells aren't harvested. They keep producing milk, which can be collected continuously.
  • The expensive part is the growth media. Cutting its cost is the biggest hurdle to affordable cell-based milk.

If you’ve read our introduction to cell-based milk, you know the basic idea: grow the cells that make milk, and let them make it. This article walks through how that happens in practice, step by step.

Every company guards its exact process, so think of this as the common blueprint rather than any one firm’s recipe.

Step 1: Source the cells

Everything starts with mammary epithelial cells: the cells that line the alveoli (tiny milk-producing sacs) inside an udder or breast.

There are a few ways to get them:

  • Tissue biopsy. A small sample of mammary tissue is taken from an animal.
  • From milk itself. Fresh milk naturally contains a small number of live cells shed from the gland, which can be isolated and grown.
  • Established cell lines. Some companies develop immortalized cell lines that can keep dividing indefinitely. Opalia, for example, describes working with an immortal line of cow mammary cells. Once a line like this exists, the company doesn’t need to return to animals for new samples.

For cell-cultured breast milk, companies use human mammary cells, typically from donated tissue.

Step 2: Multiply them

A handful of cells can’t make much milk, so the first job is growth. The cells are placed in growth media, a carefully balanced broth of sugars, amino acids, vitamins, salts and growth factors, and kept at body temperature in sterile vessels.

This is where much of the cost lives. Growth factors are signaling proteins that are expensive to make, and historically many cell cultures relied on fetal bovine serum. Most food-focused companies are moving to serum-free media, both for cost and because animal-derived serum undercuts the “no animals” promise. (More on that in is cell-based milk vegan?)

Step 3: Recreate the gland

Here’s where milk differs from meat. Cultivated meat companies grow cells and then harvest the cells themselves. Milk companies want the cells to stay alive and keep producing.

In the body, mammary cells form a single layer with two distinct sides:

  • the basal side, which faces the bloodstream and takes in nutrients, and
  • the apical side, which faces the duct and releases milk.

To mimic this, many systems grow the cells on a porous surface, often bundles of hollow fibers similar to those used in kidney dialysis. Nutrients flow on one side, and milk accumulates on the other. Because the two sides are separated, the milk doesn’t mix with the growth media.

Inside a hollow-fiber bioreactor Nutrient media flows around a porous fiber. Mammary cells line the fiber wall, take in nutrients from the outside, and release milk into the hollow center, where it flows out to be collected. Nutrient media (outside the fiber) Milk collects inside the fiber Milk out to collection Simplified cross-section of one fiber Mammary cells line the porous fiber wall Nutrients pass in from outside
Nutrients feed the cells from one side; milk is released on the other side, so it doesn't mix with the growth media.

Step 4: Switch on milk production

Cells that are busy dividing don’t make much milk. Producers use hormonal signals, such as prolactin, the hormone that triggers milk production in mammals, to tell the cells it’s time to start lactating.

Once switched on, the cells synthesize and release the key components of milk:

  • Proteins, including caseins (the proteins that make cheese possible) and whey proteins such as beta-lactoglobulin and alpha-lactalbumin
  • Milk fat, packaged in droplets surrounded by a membrane, as in natural milk
  • Lactose, the milk sugar, which mammary cells make themselves

Step 5: Collect continuously

Because the cells aren’t harvested, milk can be drawn off over days or weeks while the cells keep working. Opalia describes its process as continuous. This is a big theoretical advantage over batch processes: the same cells keep producing, which spreads their cost over more milk.

Step 6: Process and package

The collected milk is filtered and standardized for fat content, much like conventional dairy. It can then be sold as drinking milk or made into cream, butter, cheese, or yogurt.

One notable difference: conventional raw milk is pasteurized to kill bacteria picked up on the farm. Milk made in a sterile, closed system starts out cleaner. Opalia has said its product doesn’t need pasteurization, though regulators will have the final word on what processing is required.

Where it gets hard

Making milk in a lab is solved. Making it cheaply is not.

  • Media cost. Opalia has named culture media as its primary cost driver. Growth factors and purified ingredients are priced for medical research, not for food.
  • Volume. A single dairy cow in the US produced about 24,000 pounds of milk in 2025, according to USDA figures. Matching that output in bioreactors requires a lot of steel, energy, and sterile capacity.
  • Cell stamina. Cells can lose their milk-making ability over time. Keeping them productive for long runs is an active research area.
  • Completeness. Some milk components come from the cow’s blood rather than the mammary cells themselves. Replicating the full profile may require adding them back.

Sources

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