I used home made buttermilk, but this seems to happen to my feta as well as my other hard cheeses Even when I use the frozen, mesophilic DVI. This one was just a "farmers cheese". So, I started at 86, added buttermilk , then rennet, then it sat, then I cut the curd, slowly stirred for half an hour while it came up to 100. It all looked sooo beautiful when I put the curds in the press and then even when I took them out 2 hours later (slowly increasing the pressure...) Then after sitting on the counter in my kitchen for 24 hours to dry off and allow me to wax it... it bulged out a bit at the bottom overnight and then when I cut into it (because I suspected something ) I found the same old holes... ugh!
I boil everything before I start.