The Correct Answer and Explanation is:
The correct answer is b. The following Sunday.
Here is a detailed explanation of the food safety principles involved.
The key to determining the correct use by date in this scenario is a food safety guideline commonly known as the 7 day rule. This rule states that ready to eat, potentially hazardous food, like cooked taco meat, can be stored under refrigeration at 41°F (5°C) or lower for a maximum of seven days. The count begins on the day the food was prepared, which counts as Day 1.
In this situation, the taco meat was prepared on Monday. Therefore, Monday is Day 1 of its shelf life. Following this timeline:
- Day 1: Monday
- Day 2: Tuesday
- Day 3: Wednesday
- Day 4: Thursday
- Day 5: Friday
- Day 6: Saturday
- Day 7: Sunday
This means the taco meat, on its own, must be used or discarded by the end of the day on Sunday.
The critical concept to apply next is that when you combine ingredients to make a new dish, the use by date of the final product is determined by the ingredient with the earliest preparation date. This is sometimes called the “first in, first out” or “weakest link” principle. Even though you added fresh vegetables and assembled the final tacos on Tuesday, the clock for the meat had already started on Monday. The preparation of the meat is the earliest event that starts the 7 day timer for the hazardous ingredient. You cannot reset the clock just by adding new ingredients.
Therefore, the entire batch of tacos, which contains the meat prepared on Monday, inherits the use by date of that meat. The tacos must be consumed or discarded by the end of the day on the following Sunday to ensure they are safe to eat. Waiting until Monday would be Day 8, which exceeds the safe storage limit and increases the risk of bacterial growth and foodborne illness.
