The process begins with a handful of stem cells that are isolated from an animal. Initially, the volume is tiny and the cells are handled very carefully. They are mixed with medium, which is a mixture of growth factors like insulin, along with amino acids, and other nutrients that they need to grow. Then they are proliferated (multiplied) to upwards of 10M cells per mL.
After proliferating, the overall volume gets above 250 mL and shear stresses start to become an issue, meaning the cells get damaged and break apart. Traditional bioreactors use large impellers for mixing the cells and medium, along with a sparger which adds gasses like CO2 and O2. The impeller, gas bubbles, baffles, and internal surfaces are all locations where cells encounter damaging shear stresses. That’s not a problem if you’re cultivating bacteria, yeast, or other microorganisms that have a high tolerance for this. But mammal, bird and fish cells are very intolerant of such stresses, making it hard to cultivate meat. This is the first problem we address.
Contamination is definitely a problem for cultivated meat. It is one of the leading risks when scaling because if the reactor is contaminated at all, you could lose entire batches of meat, and as you can imagine, this is a huge cost hit. To avoid this, cultivated meat is grown in sterile, clean environments. The same kind of equipment you'd find in a hospital (autoclaves) is used to sterilize the equipment common in cultivated meat. There are two basic ideas for preventing contamination. One is to use single use bioreactors, which are sterile after manufacturing. This is extremely common in the biopharma industry, and is preferred because it doesn't require complex cleaning systems. Of course, anything that is single use ends up in a landfill, so thats part of the trade off as well. The other option is to use reusable bioreactors. These require a steam clean after each batch, which adds to the overall operational and build costs of the reactor. This can also generate waste products which have to be handled. Maintaining cleanliness is a challenge, but with proper laboratory practices, and the right kind of bioreactor, contamination should be less of a problem.