What happen to milk when kept at room temperature in summers?

Milk is an ideal food source for many microbes, like bacteria and fungi, which can quickly multiply and spoil milk stored at room temperature. Let's understand the process in detail:

1. Spoilage Mechanism: When milk is left unrefrigerated, the warmth of the room becomes a perfect incubator for the growth of mesophilic bacteria (bacteria that thrive at moderate temperatures). These bacteria convert the milk's lactose (natural sugar) into lactic acid, causing it to sour.

2. Souring of Milk: As lactic acid accumulates, it leads to a change in milk's pH, making it more acidic. This can cause milk to curdle and separate into curds (solid milk proteins) and whey (the liquid part).

3. Proteolysis: Proteolytic bacteria break down the milk's proteins into simpler compounds, leading to a bitter taste.

4. Lipolysis: Lipolytic bacteria can also grow and release enzymes, such as lipases, that break down milk fats and cause rancidity, giving the milk a "spoiled" or "off" flavor.

5. Microbial Growth: Unrefrigerated milk can become a haven for various other bacteria and microorganisms that can pose potential health risks. If consumed, these microbes can lead to foodborne illness and a range of gastrointestinal symptoms.

6. Accelerated Spoilage: During hot summers, the higher ambient temperature speeds up the multiplication and growth of bacteria, spoiling the milk even more quickly.

To prevent spoilage, it's essential to store milk at or below 40 degrees Fahrenheit (4 degrees Celsius) to slow down the growth and activity of spoilage-causing bacteria and ensure that milk remains safe and fresh for consumption.