I used palm sugar for the first time when we were cooking from Pure Desserts. That book uses a number of off-the-beaten-track sugars.
Anyway, when I went to one of our asian stores to buy the palm sugar, there were a few kinds. I wasn't sure what was right so I bought one kind that came in a jar and another hard kind that came in disks.
When I went to use it, I found that the jarred stuff was softer. You could scrape it out with a spoon. The stuff in disks you had to grate. (Although it wasn't that hard and wasn't really difficult to do.)
So I thought, why would I want the disks when the jarred stuff is easier to use?
Now I know why. The jarred stuff is moldy. Definitely not usable.
But the disks are doing just fine on my shelf.
(Maybe I should have refrigerated the jarred stuff. I kind of doubt if that would have prevented the mold though.)