Why must most milk in the US be refrigerated at all times while evaporated canned and cardboard containers sold Europe do not need to until they are open?

- Raw Milk: In the US, most milk is pasteurized, which kills harmful bacteria. However, some states allow the sale of raw milk, unprocessed milk that contains these bacteria, which can cause serious illnesses. To ensure the safety of consumers, raw milk must be refrigerated at 40°F (4°C) or below.

- Pasteurization: Pasteurization is a heat treatment process that kills harmful bacteria in milk while preserving its nutritional value. In the US, pasteurization is mandatory for all milk sold commercially, except for certified raw milk. Pasteurization typically involves heating milk to 161°F (72°C) for at least 15 seconds.

- Refrigeration after Opening: Even after pasteurization, milk is still susceptible to bacterial growth. To prevent spoilage, it's essential to refrigerate milk below 40°F (4°C) and consume it within the recommended "sell-by" or "expiration" dates. Keeping milk chilled slows down bacterial growth and extends its shelf life.

Evaporated Canned Milk in Europe:

- Sterilization: Evaporated canned milk sold in Europe undergoes a different process called sterilization, which involves heating milk to a higher temperature (typically 240°F or 116°C) for a longer period (usually several minutes). Sterilization eliminates nearly all bacteria, including those that can survive pasteurization.

- Shelf Stability: Sterilization allows evaporated canned milk to be shelf-stable, meaning it can be stored at room temperature without spoilage. The airtight seal of the can further prevents contamination. Shelf-stable packaging, such as Tetra Paks, may also be used, which are made of multiple layers of materials that provide barrier protection against oxygen, light, and moisture.

Cardboard Containers in Europe:

- Ultra-High Temperature (UHT) Treatment: Some milk sold in cardboard containers in Europe undergoes UHT treatment, similar to sterilization but at an even higher temperature (typically around 275-302°F or 135-150°C) for a briefer period (a few seconds). This process eliminates almost all microorganisms, ensuring long-term shelf stability.

- Aseptic Packaging: UHT milk in Europe is often packaged in sterile, aseptic containers (like Tetra Paks) that preserve the milk's quality and prevent contamination. Aseptic packaging involves sterilizing the packaging and filling it with the sterile UHT milk in a sterile environment.

It's important to note that refrigeration is not necessary for shelf-stable evaporated canned milk and UHT milk in sealed containers until they are opened. Once opened, these products should be refrigerated and consumed within the indicated timeframe.