In this guide, we will answer ‘how to tell if lactose-free milk is bad?’ Also, what is lactose-free milk, its nutritional profile and what factors affect its shelf life? is also covered.

How to tell if lactose-free milk is bad?

Lactose-free milk just like regular milk gives off an offensive bitter or sour smell when it has gone bad. The milk loses its fresh and dairy-like smell and produces an offensive and dominant spoiled odor. Other indications can be a thick or clumpy texture.

Sometimes the milk appears to be a bit pale yellow in color. It’s due to the added enzyme. If the milk doesn’t give off any offset odor but is only pale in color, it’s considered safe to use.

Different off-flavors are produced by microorganisms: (i) Sour or acid flavor is caused by Lactococcus lactis. Volatile fatty acids are produced by coliforms and Clostridium. (ii) Bitter flavors result from proteolysis and lipolysis. (iii) Burn or caramel flavor is caused by Lactococcus lactis subsp. lactis var. maltigenes, which resembles the cooked flavor of overheated milk. (iv) Miscellaneous flavors — barny flavor is caused by Enterobacter oxytocum, soapiness with ammonia production by Proteus sapolactica, malty flavor by Micrococcus, fruit flavor by Pseudomonas fragi, proteolytic flavor by Pseudomonas mucidolens, fishiness by Aeromonas hydrophila, putrefaction by Clostridium and Pseudomonas putrefaciens, and fruity and alcoholic flavors by yeasts. Lactones, which can give fruity and coconut-like flavor to dairy products, can be produced by various microbial growth (such as Candida and Saccharomyces cerevisiae) and molds (such as Penicillium notatum and Cladosporium butyricum) (1).

What is lactose-free milk?

Lactose-free milk is like regular milk but with lactase enzymes present. This lactase enzyme acts on the milk sugar (lactose) and breaks it down into its simpler compounds (glucose and galactose). It tastes the same as regular milk, texture and nutritional profile are also quite identical to regular milk.

So when it’s the same as regular milk then why has it been so much commercialized? It’s because some people are born or over time become lactose intolerant i.e. they lack the lactase in their gut making it difficult for them to easily digest it. Therefore, milk is treated with lactase enzymes to make it easier for them to digest. For lactose intolerant people, it is nowadays not necessary to completely avoid the indulgence and nutritional value of dairy products. Lactose-free dairy are very good solutions that rely on the hydrolysis of lactose into glucose and galactose with the enzyme lactase. These monosaccharides are readily adsorbed in the small intestine and prevent the occurrence of lactose intolerance symptoms (2).

What is the nutritional profile of lactose-free milk?

Just like regular cows milk, lactose-free milk contains the same amount of calcium, phosphorus, vitamin A, vitamin B12, vitamin D and proteins. A single serving (240ml) of lactose-free milk contains 8 grams of proteins.

Though it has a similar nutritional profile, lactose-free milk is sweeter compared to regular milk because of the action of the lactase enzyme on the lactose sugar which converts it into simple sugars. Since our taste buds perceive simpler compounds more prominently than complex compounds, that is why lactose-free milk appears to be sweeter (5).

Is lactose-free milk processed differently than regular milk?

The answer is maybe, why? Because despite the addition of lactase enzyme in lactose-free milk it’s also processed a bit differently. The enzyme used for the production of lactose-free dairy products has traditionally been the neutral -galactosidase derived from the dairy yeast Kluyveromyces lactis (and its close relatives Saccharomyces lactis, K. marxianus or K. fragilis) (2).

Lactose-free milk is pasteurized at a higher temperature, unlike regular milk. The process is called ultra pasteurization. It uses HTLT – high temperature less time, to yield a completely sterile end product that has a shelf life of 60-90 days compared to 1-3 weeks’ worth of shelf life of regularly pasteurized cows milk.

Lactose free milk can be produced either by batch or aseptic process. In the batch process, a neutral lactase sample is added to a tank of raw or thermized milk and, commonly, incubated for approx. 24 h under slow stirring to prevent creaming. Since the milk at this stage is not sterile yet, this process has to be performed at cooled conditions (normally 4–8 C) to prevent microbial growth. After this incubation, the milk is pasteurized, homogenized and packaged. In the aseptic process, the milk is first sterilized using the UHT procedure, after which a sterile lactase preparation is injected into the milk just before packaging. The lactose conversion in the milk will take place in the milk package. Since UHT milk is often kept in quarantine for approx. 3 days at ambient temperature, there is sufficient time for complete hydrolysis before the milk is shipped to the retailer (2).

What are the factors that may deteriorate lactose-free milk? 

Lactose-free milk just like regular milk, if stored at an improper storage temperature or is constantly being exposed to different temperature gradients will make it more susceptible to spoilage.

Another factor is the presence of microorganisms. If the milk is sterile and not exposed to the environment, it will have a better shelf life, but if the milk has been exposed there might be a chance it may go bad fast even before its actual date.

For UHT treated lactose-free milk, some additional alterations may occur, such as are sedimentation, gelation (due to a destabilization of casein micelles and further interaction with some minerals), and milk browning due to the Maillard reactions which also can cause off-flavors (3).

How to store lactose-free milk so it lasts longer?

Following are some tips you may follow to get maximum use out of your purchase (4);

  • Keep it refrigerated, especially after opening. Once milk is opened, it will last about 3-5 days after the sell-by date on the label
  • Make sure that the thermostat of your fridge is kept below 4 degrees C or 40 degrees F all the time. As above this temperature range microorganisms can thrive.
  • Never store your milk carton on the fridge door. This zone is being continuously exposed to the environment and temperature keeps shifting here why? Because we keep opening the door. so It’s best to store your carton in the main fridge body preferably within the top two shelves.
  • You may also freeze it to further extend its shelf life. By simply storing the milk in an airtight container leaves an inch worth of headspace as the milk expands upon freezing. Before using, thaw in the fridge as usual. But upon freezing the texture might appear to become grainy. This milk is still safe to use.

Other FAQs about Milk that you may be interested in.

Does Nonfat Milk Have Lactose

Does Muscle Milk Stunt Growth

Does McDonald’s Have Almond Milk


In this guide, we have answered ‘how to tell if lactose-free milk is bad?’ Also, what is lactose-free milk, its nutritional profile and what factors affect its shelf life? have been discussed.

Hope you found this helpful. Any question or comment will be very well appreciated.


  1. Lu, Michael, and Nam Sun Wang. Spoilage of milk and dairy products. The microbiological quality of food. Woodhead Publishing, 2017. 151-178. 
  2. Dekker, Peter JT, Damiet Koenders, and Maaike J. Bruins. Lactose-free dairy products: market developments, production, nutrition and health benefits. Nutrients, 2019, 11, 551.  
  3. González, Nancy Michael Rosas, et al. Changes in the stability of ultra-pasteurized lactose-free milk upon storage. Emir J Food Agr, 2020, 673-683.  
  4. Milk. 2022. The Nutrition Source. School of Public Health. University of Harvard.
  5. Dekker, Peter JT, Damiet Koenders, and Maaike J. Bruins. Lactose-free dairy products: market developments, production, nutrition and health benefits. Nutrients, 2019, 11, 551.