Unfortunately for seniors, there is one common coffee habit that can quickly turn the benefit-laden beverage into a health hazard. Experts warn that if you’re over 65, you may be more susceptible to bacterial infection if you do this one thing with your coffee. Read on to find out how to avoid serious foodborne illness from your favorite morning pick-me-up. RELATED: This Is the New No. 1 Cause of Food Poisoning, CDC Study Says. If you often rely on the microwave to revive your cooled down cup of coffee, you may be exposing yourself to harmful bacteria without realizing it. That’s because microwaves can heat food and beverages unevenly, leaving pockets of cold in the center. “Contrary to conventional wisdom, microwaves heat food from the outside in, not from the inside out,” reports The New York Times. “That can result in those all too familiar cold spots, which act as small pockets where bacteria can thrive,” their experts explain. One study published in the American Journal of Epidemiology tracked a Salmonella outbreak among picnic attendees in Alaska and found that whether an individual used a microwave to reheat their food was closely linked with whether they became ill. “Of 30 persons who ate reheated meat, all 10 who used a microwave oven became ill, compared with none of 20 who used a conventional oven or skillet,” the researchers wrote. “Compared with conventional methods of reheating, microwave ovens had no protective effect in preventing illness,” the team concluded. RELATED: Never Make This One Popular Food in Your Slow Cooker, FDA Warns. According to U.S. Dairy, you can safely leave milk out of the refrigerator for no longer than two hours before it begins to curdle and populate with bacteria. That includes even the small amount of milk you may have used in your coffee. While you may be able to drink black coffee for up to four hours before the oils inside it start to go bad, experts say you’ve got just 30 minutes—roughly the amount of time it takes for the coffee to cool—to enjoy your cup of joe at peak flavor and safety. For more health news sent directly to your inbox, sign up for our daily newsletter. While anyone can get sick from an old cup of coffee if improperly reheated, those over 65 are much more likely to become severely ill. “Older adults have a higher risk because as people age, their immune systems and organs don’t recognize and get rid of harmful germs as well as they once did,” according to experts from the Centers for Disease Control and Prevention (CDC). “Nearly half of people aged 65 and older who have a lab-confirmed foodborne illness from Salmonella, Campylobacter, Listeria or E. coli are hospitalized,” the health authority adds.ae0fcc31ae342fd3a1346ebb1f342fcb But that’s not all. The body is also more susceptible to bacterial infection over 65 because of several changes in the gastrointestinal tract. Namely, as we age, our GI systems hold onto food for a longer period of time, allowing bacteria to grow. The stomach also tends to produce less acid, killing less bacteria in the intestinal tract, says the CDC. “Underlying chronic conditions, such as diabetes and cancer, may also increase a person’s risk of foodborne illness,” the organization notes. While there’s nothing safer than simply brewing a fresh cup of coffee, experts say there are a few ways you can mitigate the risk of reheated beverages. First and foremost, you should always be sure to stop the microwave halfway through the heating process to stir your beverage, explains the Food Safety and Inspection Service (FSIS), a branch of the U.S. Department of Agriculture (USDA). This will help ensure even heating, and minimize your risk of creating cold pockets which can harbor bacteria. Additionally, you should always make sure that your coffee mug and machine are properly cleaned between uses, lowering your chances of contamination. RELATED: The CDC Just Released a Warning That You Shouldn’t Eat This Right Now.