The science behind why potato bread lasts so long.
While developing our recipe for Potato Burger Buns, we noticed that not only were the rolls incredibly soft and moist right out of the oven but, unlike other breads, they were as soft and fresh a day later. Could the potatoes be playing a role?
We baked one batch of our potato rolls according to the recipe; in a second batch we replaced the mashed potatoes with the same weight of all-purpose flour (8 ounces), adding extra water to compensate for the moisture contributed by the mash. We stored both batches of rolls at room temperature for two days.
After one day, the potato rolls were almost as moist as when they came out of the oven, while the all-wheat rolls were noticeably firm and dry. After two days, the wheat rolls were inedible, but the potato rolls remained soft and remarkably fresh-tasting.
As baked bread cools, its starches begin to crystallize, trapping water inside the hardened crystal structures. This process of “retrogradation” (more commonly known as staling) explains why bread becomes firm and appears to dry out as it sits on the counter. When bread contains potato, however, this reaction is tempered. The starch molecules in potatoes contain negatively charged phosphates that deter them from recombining, and diluting flour with potato makes it harder for the wheat starches to crystallize as well. The net effect? Potato breads stay soft much longer.