Brewed coffee is generally an acidic beverage that discourages many common foodborne pathogens, but this protective quality diminishes quickly under improper conditions. The primary risk associated with consuming coffee that has been sitting out for too long comes from the proliferation of microorganisms that can cause gastrointestinal distress. This article focuses on the safety of brewed coffee, not unground beans.
Microbial Risks: Bacteria and Mold Growth
Black coffee is somewhat resistant to bacterial growth because of its acidity. Hot-brewed coffee typically has a pH range between 4.5 and 5.5, an environment that is unfavorable for many common bacterial strains. However, this acidity only slows, rather than prevents, microbial contamination, which can be introduced from the air, the cup, or the brewing equipment itself.
Mold growth presents a distinct concern, especially if coffee is left sitting for several days or if the brewing equipment is not cleaned properly. Molds can produce mycotoxins, such as Ochratoxin A, which are toxic compounds that can survive the brewing process, though significant levels are more commonly associated with improperly stored green beans. Cold brew coffee, which is steeped without a heat step and often has a slightly lower acidity (higher pH) than hot brew, may present a different risk profile for bacterial growth. The natural antimicrobial compounds in black coffee help prevent significant growth of bacterial pathogens, but contamination from external sources remains a factor.
The Impact of Time, Temperature, and Additives
Time and temperature dramatically change the safety profile of brewed coffee. The most rapid bacterial growth occurs within the “Danger Zone,” a temperature range between 40°F and 140°F (4°C and 60°C). Coffee left at room temperature quickly enters this zone, allowing bacteria to double in number in as little as 20 minutes. The standard food safety rule advises against leaving any perishable food in this temperature range for more than two hours.
The presence of milk, cream, or sugar significantly accelerates spoilage by neutralizing the coffee’s acidity and introducing nutrients. These additives provide an ideal growth medium, causing the coffee to spoil much faster than plain black coffee. For hot-brewed coffee with dairy added, the two-hour limit for being left at room temperature is especially important to observe. Cold-brewed coffee, particularly if it contains added ingredients, should be treated with the same caution as hot brew once it is left unrefrigerated.
Recognizing Signs of Spoilage and Symptoms
Spoilage is often indicated by a change in sensory characteristics. Spoiled coffee may develop a sour or musty smell that is distinct from its natural aroma, signaling microbial activity. Visually, you may notice a slimy texture or film on the surface, or even visible signs of mold or scum, which are clear indicators that the coffee should not be consumed.
Ingesting coffee contaminated with high levels of bacteria or mold can lead to food poisoning, resulting in gastrointestinal symptoms such as nausea, vomiting, abdominal cramping, and diarrhea. While severe illness from plain old coffee is uncommon, the risk increases with the presence of dairy or if the coffee has been left out for several days, allowing pathogens to reach high concentrations. Mild stomach upset can also occur simply from consuming very old coffee due to the oxidation of its oils, which causes a rancid taste.
Safe Consumption and Storage Guidelines
Brewed coffee should be stored quickly and properly to ensure safety and maintain flavor. Plain black coffee that is not consumed immediately should be transferred to an airtight container and refrigerated within two hours of brewing. Once refrigerated, black coffee is generally considered safe to drink for up to three to four days.
Cold brew coffee concentrate can maintain its quality and safety for a longer period, often up to 10 days in the refrigerator. However, coffee that has had milk, cream, or sugar added must be treated as highly perishable, and should be consumed immediately or discarded much sooner, typically within one to two days even if refrigerated. Storing coffee in an airtight container helps to prevent microbial contamination from the refrigerator environment and slows the flavor-degrading oxidation process.