With William Byrd we're about 100 years previous to pasteurization processes. Boiling milk will keep it sweet for a few extra days. They certainly had springhouses which helped keep things cool, but even the icebox was still in the future. Boiled milk tastes different than fresh. A person might acquire a taste for it. I've read an old cookbook or two that thought it healthier - either might have been Byrd's reason. Phyllis Solter