Cheese – make a cheese sauce with edam cheese

Could be an unfinished roux (the butter, flour mixture). But most likely it's because the cheese was heated too quickly or too much, causing the protein to clump up.

Suggestions:

• Melt with less heat
• Use a double boiler (to reduce hot spots within the pan)
• Toss the shredded cheddar with cornstarch first (starch helps reduce clumping)
• Add cheese in smaller batches (easier to maintain correct heat level and stir cheese in)

I hope I'm answering the right question. Your title says "grainy" but then the rest of the question talks about "gloopy". If the problem really is grainy, I think the issue may be that you are using better cheese than in the past. Well aged cheeses tend to get a little bit drier and crystalline, and then they don't seem to melt as well. I've had grainy in that case too. Sometimes I'm happy to live with a little bit of the graininess to get the better flavor.