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Why does oat milk have a long shelf life?

Oat milk has become an increasingly popular plant-based milk alternative in recent years. Unlike dairy milk which usually lasts about a week after opening, oat milk can last for up to a month refrigerated after opening. This long shelf life is thanks to the natural properties of oats.

Oat Milk Production

Oat milk is made by soaking oats in water, then blending the mixture and straining out the oat pulp. The milk is then homogenized to break down the oat particles and make the texture smooth. Unlike nut milks like almond milk which require straining and separation of the solids, the process of making oat milk leaves many of the nutrients from the oats suspended in the milk.

The main ingredients in oat milk are simply oats and water. Some brands may add small amounts of salt, oil or other natural stabilizers. The lack of dairy ingredients is what allows oat milk to stay fresh for so long without spoiling.

Natural Preservatives in Oats

Oats contain natural compounds that have preservative properties to help prolong the shelf life of oat milk. Here are some of the key compounds:

  • Fiber – Oats are high in a soluble fiber called beta-glucan which has been shown to have antimicrobial effects. This fiber can help inhibit bacterial growth in the milk.
  • Phenolic acids – Oats contain the phenolic acids ferulic acid and p-coumaric acid. Phenolic compounds act as antioxidants to prevent spoilage.
  • Avenanthramides – These unique antioxidants found in oats also have natural preservative effects.

In addition, oats do not provide much sugar for bacteria or yeast to feed on, limiting microbial growth. The prebiotic fiber in oats may also promote growth of beneficial bacteria that outcompete harmful microbes.


Most commercially produced oat milks are pasteurized to destroy any potential pathogens before bottling. Pasteurization involves briefly heating the milk to high temperatures to kill microorganisms. Many brands use high-temperature, short-time (HTST) pasteurization which heats the milk to 72°C for 15 seconds.

Pasteurization significantly reduces the microbial counts in oat milk, allowing it stay fresher for longer. It eliminates dangerous pathogens like Salmonella, E. coli and Listeria that could otherwise grow over time. The beneficial compounds in oats combined with pasteurization give oat milk long-lasting stability.

Aseptic Packaging

After pasteurization, oat milk is typically packaged in aseptic containers. This involves filling sterilized containers in a sterile environment to prevent recontamination after heat treatment. Common packaging used includes:

  • Tetra Pak cartons
  • Plastic bottles
  • Shelf-stable boxes

Aseptic packaging seals out microorganisms, oxygen and light exposure. By preventing air from getting in, it stops oxidative reactions and aerobic microbes that could spoil the milk. The packaging maintains sterility and freshness for months.

Refrigerated Storage

Even after opening, oat milk will last longer than dairy milk due to refrigerated storage. Keeping opened oat milk chilled in the fridge slows microbial growth and enzyme activity that causes foods to deteriorate. At cold temperatures between 1–4°C, chemical reactions are slowed down significantly.

Refrigeration combined with the antioxidant content of oats allows oat milk to stay fresher for weeks after opening. Dairy milk has a more neutral pH around 6.5-6.7 which promotes microbial growth, while oat milk is slightly acidic with a pH of about 6.2-6.4. The lower pH helps inhibit bacterial growth during fridge storage.

Nutritional Profile

Oat milk is able to remain shelf-stable for so long partially due to its nutritional makeup. Here is a comparison of the main nutrients in one cup of dairy milk versus oat milk:

Nutrient Dairy Milk Oat Milk
Fat 8 g 5 g
Protein 8 g 3 g
Sugars 12 g 7 g
Calcium 300 mg 350 mg

Oat milk is naturally low in sugar and protein which are nutrients that can promote microbial growth. It also contains added calcium and vitamin D for bone health. The reduced amounts of the most perishable nutrients contribute to the long shelf life of chilled oat milk.

Acidity (pH)

Fresh dairy milk typically has a pH around 6.5-6.7, which sits in the optimal range for many microbes to grow. Oat milk has a slightly lower, more acidic pH around 6.2-6.4. This creates a less hospitable environment for many spoilage organisms.

At the natural pH of oat milk, bacteria like Listeria and Salmonella stop multiplying. A lower pH also slows the growth of yeasts and molds. The acidity helps prevent substantial microbial growth while refrigerated.

Lack of Lactose

One of the main reasons dairy milk spoils quickly is because of its naturally occurring sugar lactose. Lactose can be readily used by microbes as an energy source to fuel rapid growth. Bacteria feed on the lactose in milk, converting it to lactic acid which sours the milk.

Oat milk contains no lactose for bacteria to feed on. Without this natural sugar, microbes have less ability to proliferate. The lack of lactose contributes to oat milk’s long shelf life compared to dairy milk.

Low Water Activity

Water activity or aw refers to the amount of freely available water in a food. Bacteria require a certain level of water activity to support growth. Oat milk has a relatively low water activity around 0.98-0.99.

This lower aw makes it harder for many microbes to thrive. With less available moisture, bacterial growth and chemical reactions are restricted in oat milk. The lower water activity is another factor allowing it to stay fresh when refrigerated.

Comparison to Other Milks

Here is how the shelf life of oat milk compares to some other popular milk varieties:

  • Dairy milk – 7-10 days refrigerated
  • Soy milk – 5-7 days refrigerated
  • Almond milk – 7-10 days refrigerated
  • Coconut milk – 3-4 weeks refrigerated
  • Oat milk – 1-2 months refrigerated

The natural preservative effects of compounds like beta-glucan give oat milk better stability than other plant-based milks. With aseptic packaging and refrigeration, it outlasts both dairy and many alternative milk options.

Factors that Shorten Shelf Life

While oat milk may last up to a month past its best by date when unopened, there are some factors that can shorten its shelf life once opened:

  • Repeated temperature changes from fridge to room temp
  • Contamination from repeated opening/closing
  • Storage above 5°C
  • Signs of spoilage like sour smell, curdling, mold

Leaving oat milk out on the counter or experiencing temperature fluctuations can accelerate spoilage. Proper storage in a clean fridge below 5°C is best for maximizing the shelf life after opening.

How to Tell if Oat Milk Has Spoiled

Here are some signs that opened oat milk has gone bad and should be discarded:

  • Sour, buttermilk-like smell
  • Curdled texture/separation
  • Mold visible on surface
  • Fizzing/bubbling when shaken
  • Change in color

If your oat milk develops a thick, rope-like texture, this is not necessarily a sign of spoilage. The beta-glucan fiber in oats can cause thickness over time but is not hazardous.

Food Safety

If oat milk is mishandled, it can still grow dangerous bacteria over time. Make sure to practice food safety when storing oat milk:

  • Store in a clean fridge below 5°C
  • Keep container lid closed
  • Avoid introducing contaminants from utensils/hands
  • Use opened carton within 7-10 days
  • Do not drink if spoiled

Properly stored oat milk should be safe for a month, but use your judgment based on smell and appearance. Discard immediately at any signs of spoilage.


With its natural preservatives, low pH, aseptic packaging and lack of dairy sugars, oat milk is able to resist microbial growth and stay fresh much longer than other milks. Its shelf life extends up to a month when properly stored in the fridge. Knowing the signals of spoiled oat milk and practicing food safety will help you maximize the shelf life while avoiding any foodborne risks.