Oh shoot I had seen this in my formula too.. I was confused and thought I didn’t clean the bottle well enough. But makes sense that it is the formula.

Hi Holly! Hi! First, we want to assure you that they are totally safe, extremely normal, and are actually the result of our milk drying processes! When we convert our dairy products (like whole milk!) into our infant formula's powdered form, it goes through a high heat spray drying process, which ranges in color. Think of it like roasting vegetables in the oven—sometimes the edges will be darker as they were more exposed to the heat, as opposed to the center bits, but still totally good to eat. That being said, we always test our formula before it is sent out, so you can be sure that your formula is still absolutely safe, and you can go ahead and feed to baby.

I read in a different comment posted by the byheart team that it’s burnt fórmula and it’s safe. If you scroll below a bit you’ll see.