Final answer:
Bakers in the 18th/19th century added alum to their flour which was an adulteration practice exposed by Friedrich Accum. Alum made bread look whiter. While yeast, salt, and sugar had their roles in baking, alum was specifically used to deceitfully improve the appearance of bread.
Step-by-step explanation:
In the 18th and 19th centuries, bakers would sometimes add alum to their flour.
This practice was exposed by Friedrich Accum, who noted that alum was used to make bread look whiter, a form of food adulteration that he strongly denounced. To understand why bakers at the time might have chosen alum as an additive, it's important to understand the chemistry of baking.
While yeast has long been a staple ingredient in baking to create light and fluffy bread through the production of carbon dioxide, the use of baking powder, which can contain ingredients like sodium aluminum sulfate, is related to the same desire for a desirable texture without the longer process of yeast fermentation.
Other ingredients historically used in baking include salt and sugar.
While salt is used for flavor and to control yeast activity, sugar can be used to feed the yeast, enhancing the carbon dioxide production. Both also impact the chemical reactions during baking.
Nevertheless, adding alum (choice A) was a particular adulteration practice highlighted in the time period of question, rather than these other more typical baking ingredients.