When I bake my cake (yellow cake). I let it cool overnight on a cooling rack. The next day I goto decorate it at the bottom there are little tiny gray spots (about 4-7) on the cake. They almost look like mold. But it can not be since my cakes were made the day before. I just take a knife & scrape 'em off. I do not want anyone seeing it. Any idea what this could be or how to avoid it?

Thank you.

It sounds like something came off the cake pan or rack.

Thats what I was thinking the second time & saw it so I placed the cakes on parchment to cool.

Could they be air bubbles that have burst? My air bubbles look grey-ish sometimes.

I am not sure if they are air bubbles. They are a mold color. Is that what is looks like to you?