When it comes to wheat versus white bread, many people might make the hasty conclusion that white bread would mold more quickly, because of its refined state and simple sugars. Others might say that the wheat bread, being healthier and containing fewer preservatives, would mold first. Both of these conclusions contain some truth when it comes to mold growth, but there are many factors involved, as well as types of bread, so it is impossible to solely compare white and wheat without involving all of these other factors.
Most people today do not make their own bread, but purchase it from a grocer or baker. Therefore, it is subject to a number of processes that the consumer may not even know about. The main factors that will affect the rate of mold growth on your bread are the ingredients, processing conditions, storage conditions, and handling of the bread by all parties involved.
Most commercial loaves on the market today contain calcium propionate to inhibit the growth of fungi. An organic salt formed by the reaction of calcium hydroxide with propionic acid, calcium propionate occurs in a crystalline or powder form. This, along with other preservatives, extends the shelf life of bread, otherwise it would likely be moldy by the time it reached the store. So preservatives can play a big role in how quickly bread molds, whether white or wheat.
Water activity, or the moisture content of bread, is another factor that directly affects the rate of mold growth. To measure the water activity of bread, you can put a sample in an air-tight container and measure the amount of water that vaporizes from the product. With water being 1 and bone-dry 0, bread comes in with a water activity of about .95. Molds generally grow until the water activity drops below .81. The pH of bread, slightly acidic at 5.3 to 5.8, helps to counteract this growth, usually with the help of added preservatives.
Types of Mold
Four types of mold that grow on bread are penicillium, rhizopus nigricans, aspergillus, and mucon. These molds come in an array of colors, from green, gray and white to black. Both white and wheat bread can grow all of these types of mold.
Whether white or wheat bread, to slow mold growth, you should toast, refrigerate or freeze your bread. Toasting bread will reduce its water activity. Refrigeration and freezing will slow the chemical reactions causing mold to grow. If you buy fresh bread from a bakery, it is likely to have little or no preservatives added, so it is important to buy only what you will use immediately or freeze the extra for later use.