Lettuce is a perishable food item, and leaving it unrefrigerated for an extended period can lead to bacterial growth and spoilage. The exact time lettuce can remain unrefrigerated depends on various factors such as ambient temperature, humidity, and the initial freshness of the lettuce. In general, it's best to follow food safety guidelines to minimize the risk of foodborne illnesses.
If lettuce is left at room temperature (around 68-72°F or 20-22°C), it's advisable to discard it after being unrefrigerated for more than 2 hours. If the temperature is higher (above 90°F or 32°C), the time reduces to just 1 hour. These timeframes are crucial because bacteria can multiply rapidly at temperatures within the "danger zone" of 40°F to 140°F (4°C to 60°C).
To ensure the safety and freshness of lettuce, refrigerate it promptly after purchase or use. If you have lettuce leftovers from a meal, store them in an airtight container and refrigerate them as soon as possible. If lettuce looks or smells off, it's better to err on the side of caution and discard it to avoid any potential health risks.