[samatman]

Your last paragraph goes off the rails a bit, the diacetyl in ordinary butter is no better for your lungs than its synthetic equivalent. If there's a difference it's the amount of exposure, not whether the identical molecule comes from in vitro synthesis rather than in vivo.

[danuker]

Thank you, I did not know this. I know that factory workers exposed to concentrated diacetyl are more affected.

I suppose it matters how much of the flavor escapes into the air, but I did not know that it is naturally present in butter.

That said, butter comes with its own issues. For example, 14g/day is associated with a 1% reduction in life expectancy - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4927102/