Coffee grounds in Keurig K Cups stay fresh for a long time because of the way that they are packaged.
The cups are sealed in a such a way that makes them impervious to light, water, and air.
Also, K Cups are flushed with nitrogen prior to sealing. This step is essential to extending shelf life. Oxygen causes food to deteriorate. Therefore, many packaged foods, including chips, nuts, and crackers, are stored in nitrogen-filled containers. When a package is "flushed" with nitrogen, regular air is forced out of the container and nitrogen gas is inserted. This nitrogen then helps to keep the sealed food fresher longer. Therefore, the coffee grounds in Keurig K Cups will keep longer compared to coffee stored in other packaging methods.
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