A Supportive Environment

• Beans, peas and lentils are a staple food almost everywhere in the world, in part because they keep well and in part because they're such a nutritious food. Although the proportions vary among beans, all contain carbohydrates, healthy natural oils, high levels of protein and lots of vitamins and minerals. This makes them excellent food for humans, which is good, but also for bacteria. Dried beans are safe from spoilage because they don't contain enough moisture for molds and bacteria to reproduce, but once they're cooked, they become a highly nutritious, near-perfect breeding ground. At the right temperature, these microorganisms can reproduce at staggering speeds.

The Danger Zone

• Although there are a few exceptions, most dangerous microorganisms -- referred to collectively as pathogens -- only reproduce well at certain temperatures. Below 40 degrees Fahrenheit, or refrigerator temperature, they remain dormant to conserve energy and cling to life. Above 140 F, they're close to death and again must conserve all their resources just to survive. In the 100 degrees between those two extremes, bacteria can flourish and reproduce. This food-safety danger zone is why it's critically important to know exactly how hot the food in your warmer really is.

Keeping Beans Hot

• It's perfectly safe to keep hot foods hot for an extended period. Restaurants, especially buffet restaurants, do it all the time. The key is that their warmers are well calibrated and regularly tested to ensure that they keep the food above the 140 F limit of the danger zone. Above 140 F, your beans remain food safe, getting softer and creamier as they linger. Your only real limitation is quality, and deciding when their flavor or texture begins to suffer from the prolonged heating. However, if your warmer doesn't reliably keep the beans above 140 F, it merely provides a turbocharged incubator for bacteria.

Better Safe Than Sorry

• The best way to test the warmer is with an instant-read thermometer. Insert it into the beans at several places, not just to see whether they're hot enough but to ensure that they're hot enough all around the warmer. Inexpensive models might heat unevenly, leaving part of the dish at an unsafe temperature. If your warmer fails this test, fall back on the two-hour rule. Hold the beans for up two hours, and then package the leftovers for refrigeration or freezing. If the beans have been in your warmer for longer than that before you remember them, they should be discarded.