Tom/Neil, I have a decent supply of raw goat’s milk but sometimes add store cow milk just to make it go further. That works well for me on things like goat cheddar and parmesan but didn’t work out well with feta. The cow milk made it less crumble and less of the punch that pure goat milk gave. I have made feta with pure cow milk but that was even more like blue cheese without the blue. Not bad cheese but certainly not feta. I hope that helps.