gritty cajeta?

I made cajeta today for the first time, used the recipe in Rick Bayless's mexican cookbook. Started with 2 gallons of fresh goat milk, ended with 5 1/3rd pints of cajeta. So yummy!

I strained the cajeta in a fine mesh strainer before canning it in jars, as Bayless suggested. (he suggests straining - the canning part I added). I got a lot of small solids/residue thanks to the strainer - but when umm 'tasting' the only partially filled jar I was surprised to find little gritty texture bits in it. Not gritty like sand - but little itsy bits. Looks to me like milk proteins but I don't really know.

Anyone have any clue as to why I got these? Tastes wonderful! But of course I'd prefer 'perfect' cajeta since these are meant to give as gifts.

thanks!
Cathy