The last two batches of Feta I have made have ended up with a whole heap of swiss like holes in them. The curds aren't spongey or horrid, in fact they taste great, they are just very holey.
My work area as always is absolutely clean and sanitised, my products are all in date and there are no contaminants in the milk. My Haloumi has worked out just fine.
The only thing I wondered was would my Ginger Beer Bug and Kefir Grains (which do have lids on but are only resting on) be throwing out enough natural bacterias and yeasts to cause this?