Buttermilk in the 18th century was different from what is typically available in grocery stores today. It was the dairy by-product left over from the churning of butter. The terms “buttermilk” and “whey” were interchangeably in many texts and period dictionaries.
Today’s buttermilk is typically milk inoculated with a lactic-acid bacteria. It has a thick viscosity and a tart flavor. The same bacteria exists naturally in traditional buttermilk, giving it a tart flavor as well. Traditional buttermilk, however, is usually much thinner than modern cultured buttermilks. The lactic acid in both traditional and cultured buttermilk makes both ideal reacting agents for such chemical leavens as Baking Soda and Baking Powder. That is why many pancake, biscuit, and soda bread recipes utilise buttermilk. But chemical leavening wasn’t in popular use until the very late 18th century, and more like the early 19th century, so buttermilk would not have been used in baking for that purpose in the 1700s.
Very few references exist in the original cookbooks regarding the use of buttermilk. The “Dictionaire Oeconomique” by Noel Chomel (1725, London) suggests that buttermilk should not be discarded, but rather, it should be given to the poor.
William Ellis mentions in “The Country Housewife Family Companion” (1750, London) that some bakers would use buttermilk in place of water or milk in the baking of bread dough. This is of particular interest, as one strain of lactic-acid bacteria (Lactobacillus) that is sometimes present in buttermilk is the same genus of bacteria that is cultivated to produce sourdough bread.
Savoring the Past 
If one was to use whey left over from making cheese to replace the water in bread; what else would you have to do or not do? Would it simply be a matter of replacing the water or do I need to add or remove any leavening agent.
Hi Dean. The whey was used to replace the water. A leavening agent, i.e., barm (fresh ale yeast) or leaven (old dough) was still used. There are two forms of fermentation going on in the dough as it rises: yeast fermentation, and bacterial fermentation. It is yeast that primarily impacts the volume and crumb structure of bread, while bacteria primarily impacts the taste. The bacteria, specifically, lactobacillus, digests available lactose, converting it to lactic acid, giving the bread a tart flavor. The addition of whey or traditional buttermilk increases the amount of available lactose. Now some experimentation is needed to determine if there is a marked difference in results between using whey and traditional buttermilk. I suspect in both cases a little time will be needed during the rise (12 to 18 hours) for the lactobacillus to really impact the bread’s flavor…but without first trying it, I could be wrong and that time may be shorter.
Love your blogs and videos, I have written down all of your recipes in my own leather bound journal (small) for when I do living history programs or reenactments. I’ve even tried several of the recipes at home, and they turned out great!! Please keep them going!! How about an episode or two on meats and perpetration along with sides? Maybe a future video?!
Hi Doc. Thank you for your kind words. They encourage us greatly! We’ll keep your suggestion in mind. Thanks! We’re working toward wrapping up the bread series (it’s proven to be a very complicated topic), and then we’ll be regrouping just a bit.