It is crushed ice from forestry, the problem is that you need ice shards for that, and those only come from icy and glacial bees. Which there isn't much information about, I've never tried myself, but from what I've heard, you can get icy from wintry + cultivated in a cold biome, and then glacial from wintry + icy.
Or something to that effect anyway. Those bees are in normal forestry, you don't need extra bees, although the wiki doesn't mention them. (which is another point which adds to the confusion surrounding them)
I'm personally unsure if it's worth the bother.