What happens if you drink unrefrigerated soy milk?

Soy milk, also known as soya milk, is a plant-based milk alternative made from soaked, ground and strained soybeans. It is a popular dairy-free option for vegans and those with lactose intolerance or milk allergies. But what happens if you accidentally leave an opened carton of soy milk sitting out unrefrigerated and then drink it? Let’s take a closer look.

Does Unrefrigerated Soy Milk Go Bad?

Yes, unrefrigerated soy milk can go bad due to bacterial growth. Soy milk is a perishable product that requires refrigeration to prevent spoilage. According to USDA guidelines, opened soy milk should be kept refrigerated at 40°F or below and discarded within 7-10 days of opening. If left unrefrigerated for too long, soy milk becomes unsafe to drink due to rapid bacterial growth.

Bacteria thrive in the warm, moist and nutrient-rich environment of soy milk. Over time, levels of bacteria can multiply to dangerous amounts capable of causing foodborne illnesses. Some common bacteria found in spoiled milk products include E. coli, Salmonella, Staphylococcus aureus, Bacillus cereus, and Listeria monocytogenes. When stored properly in the refrigerator, soy milk maintains quality and safety.

How Long Does Unrefrigerated Soy Milk Last?

The exact shelf life of soy milk left out depends on factors like the storage temperature and how long the carton has been open. As a general guideline:

  • Unopened, shelf-stable soy milk can be left unrefrigerated until the expiration date on the package.
  • Once opened, soy milk should be refrigerated and consumed within 7-10 days.
  • If left unrefrigerated for more than 2 hours after opening, soy milk quality begins to decline.
  • Unrefrigerated soy milk may be unsafe to drink after 4-6 hours outside the refrigerator.

Higher temperatures allow for faster bacterial growth. On a hot day (90°F+), soy milk can go bad within just a couple hours if left out on the counter. The fridge keeps soy milk chilled below the danger zone temperature range of 40-140°F where bacteria multiply most rapidly.

Signs Soy Milk Has Gone Bad

Watch for these common signs that opened soy milk has spoiled and may not be safe to drink if it has been left unrefrigerated too long:

  • Change in smell – Fresh soy milk has a creamy, bean-like smell. Spoiled soy milk smells sour or unpleasant.
  • Change in texture – Soy milk curdles, appears chunky, watery or gelatinous when it has gone bad.
  • Change in color – The white liquid becomes yellow or grayish in color.
  • Mold – Excess moisture enables mold growth in spoiled soy milk.
  • Gas buildup – Fermentation produces carbonation and a pressurized carton.

Trust your senses – if soy milk smells, looks or tastes off after being unrefrigerated, it is safest to discard it.

What Happens if You Drink Spoiled Soy Milk?

Drinking soy milk that has been left out too long can cause unpleasant symptoms like:

  • Upset stomach
  • Stomach cramps
  • Nausea
  • Vomiting
  • Diarrhea

These symptoms may start within 30 minutes to 6 hours after ingesting contaminated soy milk. In healthy adults, symptoms are usually short-lived and improve with rest and rehydration as the stomach bug runs its course. But certain high-risk groups like pregnant women, infants, young children and the elderly may become dangerously dehydrated from vomiting and diarrhea. Seek medical care if severe symptoms last more than 48 hours.

In more severe cases, spoiled dairy-free milk can also trigger food poisoning. Bacteria like salmonella, E. coli, listeria and campylobacter are common culprits. Symptoms are similar to a stomach bug but more extreme, lasting 5-7 days. These foodborne pathogens can even enter the bloodstream and cause a life-threatening infection.

Those with compromised immune systems are especially vulnerable to complications. Medical care is recommended if food poisoning is suspected. Notify your doctor of the potential soy milk contamination source.

How to Avoid Drinking Spoiled Soy Milk

Here are some tips to keep your soy milk fresh and safe to drink:

  • Purchase soy milk in small containers to limit how long it stays opened.
  • Check “use by” dates and don’t purchase cartons near expiration.
  • Keep unopened shelf-stable soy milk in a cool, dry pantry.
  • Refrigerate soy milk promptly after opening.
  • Keep the refrigerator temperature at 40°F or below.
  • Store soy milk towards the back of the fridge where it’s coldest.
  • Finish opened soy milk within 7-10 days.
  • Don’t return soy milk to the fridge once poured. Bacteria can multiply in the carton.
  • Avoid introducing bacteria by using clean utensils and glassware.
  • Check for signs of spoilage before consuming, like an off smell or texture.
  • Discard soy milk if left unrefrigerated more than 2 hours after opening.

Can Spoiled Soy Milk Make You Sick if Cooked?

Some harmful bacteria can survive cooking temperatures. So it’s risky to assume heating or boiling will make spoiled soy milk safe to ingest. The bacteria may be killed, but toxins produced by the bacteria can withstand high heat and still cause food poisoning. For example, staphylococcus aureus can produce a heat-stable toxin that causes vomiting.

While bringing soy milk to a boil can destroy most bacteria, pathogens like bacillus cereus and some strains of E. coli produce resilient spores. These spores allow the bacteria to survive boiling, regenerate in the gut, and cause illness after being consumed. So it’s safest to discard soy milk if you suspect spoilage.

Should You Smell Soy Milk Before Drinking?

Yes, smelling soy milk before drinking is one way to check for freshness and safety. Fresh soy milk has a pleasant, creamy aroma. Spoiled soy milk gives off a sour, unpleasant odor caused by bacterial overgrowth. If the soy milk smells off, do not drink it. Odor is a useful indicator of spoilage.

However, bear in mind that soy milk may harbor dangerous pathogens before it starts smelling spoiled. Some bacterial growth will not necessarily produce a distinct offensive smell right away. So never rely on smell alone to determine if perishable soy milk is safe after being unrefrigerated. When in doubt, throw it out.

Can You Taste Test Soy Milk to Check if Spoiled?

It’s not advisable to taste test soy milk that may be past its prime. Even a small sip of contaminated soy milk could make you sick. Bacteria like E. coli and salmonella can start colonizing dairy-free milk within hours of sitting out unrefrigerated. Pathogens may be present and ready to infect your body even if the milk doesn’t taste overtly spoiled.

That said, experiencing an unpleasant or sour taste can verify soy milk is no longer fresh and should be discarded. The growth of lactic acid bacteria creates acidity that sours the usual mild taste. But don’t purposefully taste expired soy milk just to check. Discard the carton at the first signs of spoilage.

What Temperature Kills Bacteria in Soy Milk?

Heating soy milk to a bacteria-killing temperature helps reduce the microbial risks. Here are some key temperatures to know:

  • 63°C (145°F) – Kills most bacteria within 30 minutes
  • 73°C (165°F) – Kills almost all bacteria, viruses and molds instantly
  • 85°C (185°F) – Kills difficult bacterial spores within 15 minutes
  • 100°C (212°F) – The boiling point of water; kills most spore-forming bacteria

Bringing soy milk to a full rolling boil can destroy most vegetative bacteria and spores. However, some toxins released by pathogens may remain stable at boiling temperature.

Pasteurization involves heating to at least 145°F for 30 minutes or 161°F for 15 seconds. This industry standard process kills pathogens in milk products, while preserving nutrition and flavor. Ultra-high temperature (UHT) processing heats milk to 280°F for 2-4 seconds, allowing shelf-stable cartons to keep for months unopened.

What Kills Bacteria Faster – Microwave or Stovetop?

Method Speed Efficiency
Microwave Very fast Less consistent heat distribution may allow bacterial survival.
Stovetop Slower Even, sustained heat ensures pathogenic bacteria are destroyed.

A stovetop brings soy milk to a high enough temperature to kill bacteria more reliably. Microwaves speed up heating, but have less consistent heat penetration. Bacteria could survive if there are cold spots in microwaved milk. For guaranteed pathogen destruction, it’s best to thoroughly boil soy milk on the stovetop.

Can You Save Spoiled Soy Milk in Smoothies?

It’s risky to try to salvage spoiled soy milk by using it in smoothies or protein shakes. Any bacteria or toxins will not be neutralized by blending with other ingredients like fruits, vegetables and ice. Pathogens may even thrive in the nutrients provided by fresh produce in a smoothie.

Likewise, the acidic pH of a smoothie isn’t guaranteed to kill microbes. E. coli, for example, can survive acidic environments. And while blending may break up curdling, it doesn’t eliminate bacterial contamination.

For food safety, it’s best to discard the entire carton of soy milk at the first signs of spoilage. Using small batches and frequent grocery trips can help prevent having to throw out a large amount of expired soy milk.

Should You Still Cook or Bake With Spoiled Soy Milk?

It’s not worth the health risk to use spoiled soy milk in cooked or baked foods. Even if the end dish is heated thoroughly, bacterial toxins can withstand high cooking temperatures. Toxins may not be destroyed even if the bacteria itself is killed.

Potentially contaminated soy milk is safest discarded altogether. Bacteria can also spread around the kitchen if used in recipes, contaminating utensils, countertops and appliances. Don’t cook, bake or prepare food with soy milk you suspect has spoiled.


Drinking soy milk that has sat unrefrigerated for too long can lead to digestive upset, food poisoning and other unpleasant illnesses. Soy milk requires continuous refrigeration after opening to control bacterial growth. Leaving it out on the counter for more than 2 hours after opening can be dangerous. Always store opened soy milk properly in the fridge, observe expiration dates, and inspect for signs of spoilage before drinking. When in doubt, throw it out. Discarding a questionable carton is better than risking your health.

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