How long can milk last unrefrigerated?

In this brief guide, we are going to answer the question “How long can milk last unrefrigerated?”, discuss answers to other related questions like how does milk spoil and how to store milk.

How long can milk last unrefrigerated?

According to the US Food and Drug Administration (FDA), milk can be left out of the fridge for only 2 hours. This is because the room temperature, or the temperature range between 40 to 140 degrees Fahrenheit, is a perishable commodity for microorganisms, particularly bacteria. So, the 2-hours benchmark can become 1 instead, in case the temperature exceeds 90 degrees Fahrenheit.

How does milk spoil?

Milk is home to bacteria, such as Lactococci and Lactobacilli. At temperatures above room temperature, these bacteria breed and reproduce. These probiotic bacteria change the milk sugar, lactose, into its compositional units; glucose and galactose. Later on, the formation of lactic acid starts, as proved by the familiar tangy smell and taste. As the casein develops, the curdling process starts. As milk deteriorates further, the bacteria take over the fats, which causes the occurrence of molds.

Spoilt raw milk may become inedible as it curdles and gains its distinct sour taste and odor. However, it does not need to be discarded, as curdled milk is used to make cheese, cream, and kefir.

On the other hand, pasteurized milk does not become sour due to the absence of bacteria that are responsible to cause the milk to curdle. Instead, it rots and becomes unfit for consumption.

When the milk is spoiled, it develops undesirable characteristics. Even if milk seems to be safe, you can expect bacterial growth to start at a temperature greater than 40 degrees Fahrenheit. As milk spoils, you can detect a rancid and sour smell. The texture and consistency of the milk change too and the color becomes pale with a yellowish tinge.

Drinking spoiled milk can cause you to be a victim of food poisoning with general symptoms of vomiting and diarrhea. Therefore, it is better to just toss off the spoiled milk rather than risking your health.

How to store milk?

So, from the above discussion, we come to an end that the milk should not be left out of the fridge and especially not overnight. 

Aseptic milk, packaged after processing at an Ultra High Temperature, will last for 6 months if its seal was left intact. However, an opened tetra pack will spoil if left out of the fridge overnight. Pasteurized milk can not be left out at room temperature for more than 2 hours.

The pasteurization process kills bacteria by heating the milk at high temperatures. After potentially harmful microorganisms destroy, then it is aseptically sealed to ensure its longevity. Once the seal has broken, pathogenic microorganisms cause the milk to spoil.

Traditional milk, on the other hand, does not undergo such a process. Therefore you can expect it to have a shorter life, even if it has an intact seal.

Other FAQs about Milk which you may be interested in.

Can you use evaporated milk instead of regular milk?

Can diabetics drink chocolate milk?

How much does a gallon of milk weigh?

Pasteurization vs UHT treatment

Milk bought from a store is in either of the three forms; raw, pasteurized, or UHT treated. However, milk is sometimes only pasteurized and not subjected to the ultra-high temperature.

Pasteurized milk is not shelf-stable and needs to be refrigerated at all times. In pasteurization, the milk is first chilled and then heated. Milk is allowed to move between heated stainless steel plates at a temperature of 161 degrees Fahrenheit. The heating occurs for 15 seconds only. Then the temperature is bright down again, from 161 degrees Fahrenheit to 39 degrees Fahrenheit, before it is packaged and distributed.

As pasteurized milk is heated to a cooler temperature, it is more prone to spoilage. Some bacteria tend to survive during the process, thus the milk requires constant refrigeration to keep these bacteria from growing and multiplying. Pasteurized milk will spoil if left out overnight. It has to be refrigerated at 2 to 6 degrees Celcius. The shelf life lasts for 2 to 5 days.

Ultra-high temperature treatment differs slightly, as milk is heated at 136 to 145 degrees Fahrenheit for only 2 to 4 seconds. So, it lasts longer than pasteurized milk and hence, is processed and sold at room temperature. After it has opened, a UHT milk pack can go bad, if left at room temperature overnight. It may not show any sign of spoilage, but drinking or using UHT milk that was left out overnight is not recommended.

In contradiction, raw milk does not undergo any heat treatment and hence, has the shortest shelf-life. When properly refrigerated, you can keep raw milk for 7 to 10 days. The presence of bacteria, such as Lactobacilli, makes the milk spoil quickly and so it can become unsuitable for consumption sooner than the heat-treated counterpart.


In this brief guide, we answered the question “How long can milk last unrefrigerated?”, discussed answers to other related questions like how does milk spoil and how to store milk.


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Hi, I am Charlotte, I love cooking and in my previous life, I was a chef. I bring some of my experience to the recipes on this hub and answer your food questions.