Skip to Content

How Does Milk Spoil

How Does Milk Spoil

How Does Milk Spoil

Milk spoils when bacteria multiply rapidly in warm temperatures. Bacteria convert lactose into glucose and galactose, producing lactic acid. This lactic acid forms a curd that can quickly curdle the milk within a day. When the milk starts curdling, it is considered spoiled and should be discarded immediately.

Milk is compromised due to the overpopulation of bacteria, reducing milk quality, taste, and texture. Milk spoilage is caused by an overpopulation of bacteria, which reduces the texture, flavor, and overall quality of milk.

Like sour milk, spoiled milk will also eventually separate, but in this case, it has done so due to the bacteria from the spoilage, not good bacteria. Pasteurization lowers the number of bacteria in the milk, which, in turn, increases the time it has to go bad.

By the way, if you’re interested in Can You Eat Cork, check out my article on that.

Understanding Pasteurization: Impact on Bacteria Growth and Milk Spoilage

Pasteurization does not, however, work on every single bacteria; those hardy survivors ultimately make the milk spoil. After opening your homemade milk, new bacteria may get inside and grow, ultimately leading to the spoilage of your milk. If temperatures exceed 40F, the bacteria can grow in the milk, causing the rot and the smell.

At room temperature2 hours
In refrigerator12-14 days
Temperature and storage (shelf life) of milk.

Utilizing Heat Treatment for Baking with Spoiled Milk: Lowering Health Risks and Enhancing Flavor

If you use rotting milk for baking, the oven heat will kill off the most harmful bacteria, so you have a lower chance of getting ill.

As certain non-harmful microbes grow, they make enzymes that help them break down milk, causing it to curdle and produce that “off” smell that we associate with spoiled milk. Milk is kept cold (in a refrigerator) to slow the growth of these remaining microbes.

Some non-harmful microbes will still grow, and it is the growth of these non-harmful bacteria that causes milk spoilage. Psychrotrophic, or cold-resistant, bacteria cause refrigerator spoilage, and the rate of psychrotrophic bacteria is similar for both types of milk.

Often, it is the psychrotrophic bacteria that grow under cold conditions that are the culprits for spoiling your milk. Milk production involves multiple steps aimed at killing off the psychrotrophic bacteria in order to prolong the shelf-life.

Learn how long it takes for milk to spoil out of the fridge

What causes milk to spoil?

The growth of bacteria and other microbes, which prefer the nutrient-rich environment of milk, is the main cause of milk spoilage. Milk spoiling is caused by several variables, including:

  • Microbial Growth: Milk naturally contains microorganisms, some of which help make yogurt and cheese, among other dairy products. However, some bacteria have the potential to cause spoiling. The nutrients in the milk are used by the bacteria as they grow, changing the milk’s flavor, aroma, and texture. Additionally, pathogenic bacteria can create poisons that are dangerous to consume.
  • Temperature: Because milk is a very perishable food, temperature is a key factor in deciding how long it will stay fresh. Bacterial growth thrives in warm temperatures (over 40°F or 4°C), which hastens food degradation. The shelf life of milk is increased by cold temperatures (about 0-4°C or 32-40°F).
  • Contamination: To avoid introducing hazardous bacteria into the milk, proper hygiene and sanitation procedures must be followed during milking, processing, and packaging. Equipment, surfaces, or hands that have been contaminated might introduce bacteria that cause spoiling.
  • Exposure to light: Light, especially UV radiation, can cause vitamin and nutrient breakdown in milk, which can affect the flavor and cause spoiling. To reduce light exposure, milk is frequently packed in opaque containers.
  • Air Exposure: Exposure to air can cause milk’s lipids to oxidize, which can cause off-flavors and spoiling. Milk containers are sealed to reduce air contact because of this.
  • Enzyme Activity: Milk’s flavor and texture may vary due to its enzyme content. For instance, the breakdown of fats by lipase enzymes can result in rancid flavors.
  • Changes in pH: As bacteria break down milk constituents, they may create acids that cause the pH of the milk to decrease. The milk’s flavor, consistency, and stability may change.

Milk should be kept at the right temperature, often in the refrigerator, and with excellent cleanliness practices to increase its shelf life. The dairy sector also extensively uses pasteurization, a heat-treatment procedure that kills hazardous germs and lengthens the shelf life of milk and other dairy products.

To learn about Does Sugar Go Bad, check out my article where I cover everything you need to know.

Why does milk spoil even when refrigerated?

Due to various circumstances, milk can still deteriorate even when refrigerated, despite the cold temperature delaying the growth of spoiling germs. The following are some causes for milk to go bad in the fridge:

  • Initial Contamination: If milk was previously tainted with spoilage organisms before refrigeration, those organisms could continue to grow and cause deterioration even at lower temperatures. Proper handling and hygiene are essential throughout milking, processing, and packaging to reduce early contamination.
  • Bacterial Strain Variability: Some bacterial strains are more hardy and can endure and grow in frigid environments. Although their growth may be slowed, but not necessarily completely stopped by cold conditions.
  • Temperature variances: Although refrigerators generally maintain a constant temperature, there may be very few temperature variances in various compartments. These changes may provide environments that are better suited for developing bacteria.
  • High Bacterial Load: If the initial bacterial load of milk is high, even a slower rate of development in the refrigerator might cause significant bacterial proliferation over time.
  • Extended Storage: While refrigeration greatly lengthens the shelf life of milk, it cannot completely fend off deterioration. Bacterial activity can eventually cause deterioration over time, even at freezing temperatures.
  • Improper Sealing or Packing: Even in a refrigerated environment, improper sealing or packing can expose milk to air, light, and pollutants, hastening the spoiling process.
  • Enzymatic Activity: Even at lower temperatures, the naturally occurring enzymes in milk can continue to induce chemical reactions and changes that result in spoiling.
  • Cross-Contamination: If other foods in the refrigerator go bad and produce spoilage bacteria, they may cross-contaminate milk and speed up the decomposition process.

Follow prescribed handling and storage procedures to reduce the risk of milk spoiling. These procedures include ensuring the milk is well packed, kept at the proper temperature (often between 32 and 40 degrees Fahrenheit or 0 and 4 degrees Celsius), and eaten within the suggested time range.

It’s vital to read the label and abide by the storage directions because different milk varieties (such as whole milk, skim milk, and ultra-pasteurized milk) may have varying shelf lives.

Click on this Link if you want to learn How Long Can You Keep Salad In The Fridge.

How is it possible to detect if milk has gone bad?

Lactic acid is produced by bacteria when milk goes bad, which gives spoilt milk its unpleasant odor. In addition, rotting can be identified by the appearance of a yellowish tinge and a lumpy texture.

There are several telltale signs that your milk has gone bad and should not be consumed, including a sour flavor and odor, a change in color, and a lumpy texture.

What happens if you drink milk that has gone bad?

If you take just a little bit of spoiled milk, you probably won’t have any symptoms other than the awful taste. When consumed in larger quantities, spoiled milk can cause stomach discomfort, manifesting as nausea, vomiting, and diarrhea, similar to the symptoms of a foodborne illness.

Ingestion of spoiled milk typically results in symptoms that disappear between 12 and 24 hours after the initial exposure.

Skip to content