Cheese's biggest enemy: light and oxygen
Cheesescience.org turned 36-months-old a few days ago. In honor of that let’s talk about the most prolific cheese defect that occurs in the marketplace – light oxidation. It’s something cheesemakers have very little control over. However, it is a problem of pandemic proportions in the cheese retailing world.
Let’s tackle the nomenclature. As the name implies, light oxidation involves both light and oxygen. For our purposes light oxidation refers to the chemical reaction of fat molecules with oxygen, catalyzed by light. In other words, oxygen attacks the fat in cheese with the help of light; also known as lipid oxidation, lipid peroxidation, photo oxidation, and oxidation. Lipid is the technical term for fat. The end products of oxidation are a menagerie of bad-tasting chemical compounds, not to mention a bleached appearance.
It all starts with fat. As we’ve learned before, fat occurs in structures called triglycerides. Triglycerides are made of fatty acids. Some of these fatty acids are “unsaturated”. This means that their structure is a little different than “saturated” fatty acids. For our purposes what we need to know is that unsaturated fatty acids are more prone to oxidation reactions than their saturated counterparts. If you’d really like to know some of the nitty-gritty chemistry contact your local food chemist.
Oxygen reacts with these fatty acids and sets a cascade of reactions in place. Light helps catalyze, or speed up, these reactions. This means in can take just mere hours for the effects of light oxidation to be noticed; both visually and gustatorily. All of this is not to say that fatty acids are the only things that break down. Other compounds, like β-carotene, can break down. This leads to the bleached appearance. Many different things can speed up these reactions. Heat and metal are the big ones, as well as light of course.
This process results in the formation of many different molecules. Many of these can contribute off-flavors like “cardboard”, “crayon-like”, or “plastic”. In fact, many people misattribute a plastic-y taste in cheese to the plastic wrap it’s wrapped in. The plastic itself is pretty inert. What they’re actually tasting is light oxidation!