Originally Posted by Cheesefood
Yes. There's a chance that wild yeast will start converting your wort, which may give some off tastes.
Cover it well and you'll eliminate some of the possibilities.
Fairly low, that chance. Most steeping grains contribute little, if any, fermentable sugars to the mix. If they aren't fermentable, then there is nothing that wild yeasts can jump in their with to start fermentation.