Light and Growth

• Roots and bulbs including potatoes, carrots, onions and garlic are all dramatically affected by the presence of light. They'll keep for months in a cool, dark setting, but light stimulates their growth. The starches and sugars in these long-storage staples are designed to fuel the next year's growth. So when they sprout in the presence of light, the root or bulb itself is rapidly consumed or spoiled, in human terms. This is especially crucial with potatoes, because sprouting potatoes produce dangerously high levels of toxic alkaloids such as solanine. The alkaloids are concentrated in the potato's sprouts, skin, and the telltale band of green-tinged flesh beneath the skin. They can cause serious illness or even death, so keeping your potatoes in the dark is a priority.

Light and Staling

• Light also has the effect of speeding oxidation in many foods. Oxygen is a highly reactive element, and over time it breaks down the molecules that give foods much of their pigmentation, flavor and nutrition. How light accelerates this process isn't fully understood, but its effect is clear. For example, a bottle of paprika left on the counter will quickly lose its vivid red color and fresh flavor. Nutrients including vitamins A, C, D and many of the B vitamins are similarly affected, which doesn't make your food less safe but does impair its value and taste. Liquid foods, and powdery foods such as ground spices, are especially vulnerable because they allow light to penetrate.

Light and Off-Flavors

• Light also speeds oxidation in oils and fats, leaving them rancid and unpalatable. Foods high in unsaturated fats, such as delicate olive or nut oils, are especially susceptible. They'll quickly lose their subtle flavors, becoming strong and rank. Milk that's exposed to strong light through clear packaging is also vulnerable, developing distinct off-flavors through a combination of fat oxidation and breakdown of its proteins. Brewers face similar problems, because light causes flavor compounds in hops to break down and create a potent, sulfur-based, "skunky" flavor and odor. That's why beer is almost invariably packaged in cans or dark-tinted bottles.

Keep 'Em in the Dark

• Keeping your food safe from the damaging effects of light is a relatively straightforward process, once you're aware of the problem. Discard your countertop spice rack and transfer your bottles of spices to a closed cupboard instead. Store your dry goods in opaque canisters rather than glass sealer jars, whenever possible. If your pantry shelves are open to ambient light, improvise a curtain or small partition and move items with clear packaging behind its shelter. Better yet, avoid clear packaging whenever possible. Buy your spices in tins rather than bottles, and transfer oils from clear to dark bottles or opaque decanters.