What Makes Milk Spoil?

By Julie Boehlke

Milk is Pumped Fresh From a Cow

What Makes Milk Spoil?

Dairy cattle are prevalent in rural areas across the world. Holsteins are the most prominent producer of milk that can be made into several types of dairy products. Everything from cheese, ice cream, sour cream and cottage cheese are just a few of the products derived from cow's milk. A dairy cow most generally needs to be milked up to twice a day, every day. Dairy farms typically have milk pumping systems that can pump all teats at the same time, effectively and efficiently within minutes. In the milk pumping station as well as the holding station, the area must be sterilized to prevent the growth of bacteria. Once the milk is pumped from the cow it is then transferred to a holding tank. From the holding tank, a large truck will arrive and take the milk to a distribution plant. At the distribution plant the milk is sterilized or homogenized and then transferred to containers to be distributed to consumers.

Milk is Delivered to the Store or Home

Once the milk has been poured into containers, it will then be taken to stores to be sold to consumers. During transportation, it is essential that milk be kept at temperatures around 45 degrees Fahrenheit but not below 32 degrees. While milk is being transported it is usually done so in a cooler or refrigerated truck so that a consistent temperature is kept at all times, as this assures the freshness of the milk before it reaches the consumers.

How Milk Begins to Spoil

Milk will spoil if the temperature of milk adjusts too much in varied temperatures. When an increase and then a rapid decrease in heat occurs, bacteria such as lactococci and lactobacilli can form. If the milk gets too warm, it can spoil and actually curdle toward the bottom of the jug; this is typically due to the lactose content in the milk. Once the milk curdles, the milk is considered spoiled and should not be consumed and should immediately be discarded. Milk is the freshest from the day it was pumped from the cow, but it takes up to three to five days for the milk to reach store shelves, which is why most milk jugs or cartons must carry an expiration date. The expiration date is typically visible at the top of the jug or carton and the milk will start to naturally spoil around that date. Cow's milk is generally fresh for up to 14 days after the pump date. When opening milk, there should be no odor whatsoever; if the milk is spoiled it will smell sour and even foul. The color will most likely stay white but one should not consume the milk if it has a tainted or sour smell. Milk actually spoils when bacteria converts the lactose into glucose and galactose, which results in the production of lactic acid. Lactic acid produces casein and then forms a curd that can quickly allow the entire amount of milk to curdle within 24 hours. As bacteria forms on the sugary butterfat, mold also begins to grow and aids in causing the milk to spoil even further.