I need your help. I recently made a cake for a bridal shower. Everyone was happy with the cake, but I heard from the bride's mother that the buttercream was "grainy" or "gritty", as though regular sugar had been used instead of the confectioners' sugar I always use. Does anyone have any suggestions as to what might have happened, and how to avoid this in the future?

If you are using a 0 transfat shortening, this may be your problem. You need to use a High Ratio shortening such as Alpine, Sweet tex or CK. I live in NE PA & found that Wegmans store brand works for me as I would have to order these other brands online.
My favorite Buttercream recipe is Edna's Crusting Cream Cheese Buttercream, it doesn't have that slick shortening taste that other buttercreams have. She also suggested to add whole milk instead of water to the recipe if you can't find High Ratio.

http://www.designmeacake.com/recipes.html

Another reason might be your powdered sugar, needs to be high quality. I use Domino but others have used C &H. Just look for pure cane on the label stay away from beet sugar which is used in lower quality powdered sugar. Hope one of these solutions works for you. Good Luck!

Did you taste the icing, too? Or has anyone else confirmed this? Just a thought, but sometimes people exaggerate or find fault when they are not happy about other issues.

If it was a crusting buttercream, it could be the crust on it that she was feeling.

Also if you use a off or store brand powder sugar it could be being made with beat sugar, and that will cause problems.

I use crisco, with no trans fats, and don't have a gritty tasting icing. High Ratio shortening isn't just shorting with transfats in it.

It could very well have been your powdered sugar. The bakery I worked for had that same problem a few times and it was the sugar. Did you taste your frosting before applying? The brand we used was Dominoes and normally no problems at all, but apparently somewhere along the line there was a really bad batch.

It's happened to me before. We just assume all confectioners sugar is equal. They are not!

I use dominos. I also have a membership to costco. Their powdered sugar is a different brand but has such a gritty texture that just does not go away.

Stick with brands that you know works well and also take a taste of the icing before you add them to your cakes, just in case.