If you are using store bought milk, the pasteurization will be automatically controlled and very standardized. With farmstead milk, it is more luck of the draw. I know how much calcium I use, I know the the floc time, and how well the curd sets. With the over pasteurization, my curds shattered into smaller pieces, so I knew what the problem was. If this happens with store bought milk you can try increasing calcium the next time or just cange brands.