How Bad Is It Really to Drink Old Coffee?

The average American drinks just over three cups of coffee per day, according to the National Coffee Association — and that's understandable, considering it tastes good, delivers a jolt of much-needed energy and even offers some health benefits.

Many return to the coffee maker in the afternoon for a midday pick-me-up. Some coffee makers have a feature that keeps the coffee hot for a short period of time, so it's easy to make repeat visits to fill up your cup.

After a certain point, you may start to wonder when your coffee will go bad. Brewing a new pot may help you avoid a bad taste, but if it's black, there's probably little risk to your health. Here, we take a deep dive into how long you have before your brewed coffee is no longer drinkable.

After you brew a cup of coffee, you may wonder if the clock starts ticking. Leaving it on the coffee maker's hot plate does buy you a little bit of time. Your coffee maker might have a function that keeps the coffee hot for a predetermined amount of time.

Once that time is up, it will slowly start to cool and lose its freshness, which changes the flavor of coffee. After about 30 minutes at room temperature, the flavor will be compromised considerably. But if you're not concerned about taste, there's likely nothing to worry about.

If you're a coffee connoisseur and you enjoy the taste of your brew, you should aim to drink your coffee as soon as possible before it cools down to room temperature.

Day-old coffee will taste dramatically different, and not in a good way. But it's still relatively safe to drink. "You can drink day-old coffee if it's black and without any milk products," says registered dietitian Supriya Lal, RD.

Old coffee probably isn't dangerous, according to the National Coffee Association. Use your best judgment before drinking a cup of coffee — how does the coffee look and smell?

If you didn't personally brew the coffee, you may want to be more careful about it. Coffee served in restaurants or coffee shops should be served steaming hot, according to the CDC. Avoid warm or room-temp coffee that has been sitting out, as there's a higher risk for contamination.

There isn't a lot of scientific research that suggests how long you have until brewed coffee goes bad. Most of the evidence is anecdotal. Some sources say you have 24 hours, while others suggest drinking your coffee within four hours at room temperature or a few days if refrigerated.

The general rule is that you have two hours to eat food left at room temperature, according to the USDA, but it's unclear if this applies to brewed coffee.

"If your coffee has added ingredients like milk or other dairy products, it should be properly stored in the refrigerator and reheated before drinking to lower the risk of foodborne illness," Lal says.

Milk can last in the refrigerator for up to seven days, according to the USDA. Coffee with milk or coffee creamer in it may be safe to drink for up to a week when refrigerated, but it may not be as enjoyable as freshly brewed coffee.

If you left your mug of coffee with milk out on the counter or on your desk, you have a much shorter time frame to finish it. Drink milk, or coffee with milk, within two hours of being left out at room temperature, according to the Mayo Clinic.

Refrigerating your coffee changes the rules a little bit. When it comes to helping your brewed coffee last in the fridge, make sure to keep it properly.

"Store self-brewed coffee in a sealed container and place it in the refrigerator," Lal says. "Drink it within 72 hours to ensure freshness and quality."

Drinking day-old coffee isn't ideal, but if it's your only option, go ahead. There isn't a lot of scientific research on the shelf life and expiration of brewed coffee, so use your best judgment and when in doubt, throw it out.