I accidentally blended yogurt in a glass blender with metal blades that I wanted to keep pareve. No sharp foods in the stuff being blended, but I put hot coffee in the mixture that might have been YSB and might have touched the metal blades. We want the food to stay pareve to be served with meaty or milky food.
If kashering is needed, can I pour boiling water into the pitcher just enough to cover the blades?
Pouring hot water directly into the blender on to the blades would be sufficient. Make sure to clean the areas being kashered well before pouring the water over them
From your question it isn’t clear whether the hot coffee was put into the mixture before it was added to the blender, making it iruy kli sheini or if it was poured into the blender and then the yogurt was put on top of it, making it kli sheini. Regardless, even in the worse case, assuming that the mixture was hot, still the metal blades didn’t absorb anything milky in a way that is worse than kli sheini. Therefore pouring water onto it, which is iruy kli rishon will definitely suffice.