Please be assured that the residue is not harmful, and it can be removed easily.  The residue is from a mechanical polishing process that is used to make the stainless steel bowls shiny. Occasionally, new mixer bowls may have residue that cannot be removed in the dishwasher or by hand washing. It can discolor food items mixed in the bowl, but it is not harmful. This is a common occurrence in polished stainless products.

We recommend making a baking soda paste with baking soda and water to use to clean the bowl. Once you have scrubbed the bowl with the baking soda paste, and have rinse it with hot water, use a paper towel to check if there is still any grey residue that comes off the bowl. If there is still some residue, please run the step again.

You may also try to use some olive oil, spread it around inside the bowl. Let the oil sit for several minutes, then wipe the oil out. After removing the olive oil, wash the bowl with a hot water and good dish detergent.

You may also try a mix of lemon juice and salt and wipe clean the bowl with that mixture, but we have found that the baking soda paste seems to work most effectively between the food safe options to clean the residue from stainless steel bowls.