Soy milk, like other plant-based milks, does not contain the same proteins and sugars found in dairy milk that can spoil quickly at room temperature. However, leaving soy milk out too long can still pose some risks.
Can soy milk go bad?
Yes, soy milk can go bad if left unrefrigerated. Soy milk is a perishable food product that needs to be stored properly to maximize its shelf life. Like other plant-based milks, soy milk contains some nutrients that can support microbial growth when left at room temperature for too long.
The proteins and sugars naturally present in soybeans provide a food source for bacteria. And soy milk is made with added vitamins and minerals that can also nourish pathogens. So if contaminated and left unrefrigerated, soy milk can become a welcoming environment for microbial growth.
How long can soy milk sit out before it goes bad?
An unopened, shelf-stable carton of soy milk can be safely stored at room temperature for several months. Once opened, it should be refrigerated and will stay fresh for about one week after opening.
If refrigerated soy milk is left out at room temperature, it can start to spoil after just 2-4 hours. The warmer the temperature, the faster it will spoil.
| Time Left Out | Room Temperature | Risk of Spoilage |
|---|---|---|
| Less than 2 hours | Up to 77°F (25°C) | Low |
| 3-4 hours | 70-90°F (21-32°C) | Moderate |
| Over 4 hours | Over 90°F (32°C) | High |
As you can see from the table, soy milk left out for just a couple of hours at room temperature may be fine to consume if it has been kept relatively cool. But leaving it out for longer than 4 hours, especially in hot conditions, significantly raises the risk of spoilage.
How can you tell if soy milk has gone bad?
There are a few simple ways to check whether your soy milk is still safe and fresh to drink:
- Check the expiration date – This will give you an idea of how long the soy milk should last after opening if properly refrigerated.
- Look for changes in color or texture – Fresh soy milk is white and has a smooth, creamy consistency. If it starts to separate, looks curdled, or changes color, it’s likely bad.
- Smell for sourness – Soy milk that has soured or spoiled will have a distinct sour odor.
- Taste for sour flavor – Sour or bitter flavors are a clear sign your soy milk has spoiled.
If your soy milk displays any of the above characteristics, it’s best to throw it out. Don’t taste it if the smell or appearance clearly indicates spoilage.
What causes soy milk to spoil?
There are a few main culprits that can lead to soy milk spoilage:
- Bacterial growth – Bacteria are present everywhere, so improper storage allows them to contaminate and propagate in the nutritious soy milk.
- Yeast and mold – Exposure to air and warmth permits yeasts and molds to grow, causing spoilage.
- Chemical changes – The proteins and fats in soy milk can break down over time, especially with warmth and exposure to air.
To limit these spoilage factors, soy milk needs to be stored sealed at cool refrigerator temperatures below 40°F (4°C). The colder it is stored, the longer the soy milk will last.
Can spoiled soy milk make you sick?
Consuming spoiled soy milk can potentially make you sick, but serious illness is unlikely.
If soy milk is left unrefrigerated long enough, harmful bacteria like salmonella, listeria, or E. coli could grow and contaminate the milk. Drinking milk harboring these pathogens can then lead to food poisoning symptoms like:
- Nausea
- Vomiting
- Diarrhea
- Fever
- Chills
- Stomach cramps
However, this level of bacterial contamination doesn’t happen too quickly with plant-based milks compared to dairy. So unless soy milk was left out overnight or longer, foodborne illness is not common.
More often, consuming spoiled soy milk simply leads to temporary stomach upset or discomfort. The changed flavors and textures can be unappealing. So it’s smart to toss soy milk that’s clearly soured instead of taking a chance drinking it.
How to store soy milk properly
To get the most out of your soy milk and avoid spoilage, follow these storage tips:
- Purchase soy milk in small containers if you don’t use it frequently so it gets used up quicker.
- Check the “best by” date and use within 5-7 days of opening.
- Keep soy milk sealed until you are ready to pour it.
- Store opened soy milk in the refrigerator, never on the door.
- Don’t return soy milk to the fridge if left out more than 2 hours.
- Keep refrigerator below 40°F (4°C) and store soy milk toward the back.
- Avoid temperature fluctuations that can shorten shelf life.
- Don’t mix fresh soy milk with old soy milk.
Following these guidelines helps limit bacterial exposure and slow chemical breakdown of the proteins and fats in soy milk after opening. With proper refrigerated storage, soy milk should stay fresh for about one week past its “best by” date.
Can you fix or save spoiled soy milk?
Unfortunately, there is no way to rescue soy milk once it has truly spoiled. The bacteria and chemical changes that occur are not reversible through cooking methods.
Heating or boiling spoiled soy milk can kill some bacteria, but it does not get rid of the toxins they produce. Off flavors from chemical breakdown will also remain. So it’s not recommended to consume soy milk if you suspect it has gone bad.
Your best option is to identify and toss spoiled soy milk so you don’t risk getting sick from drinking it. And take steps to prevent spoilage in the future by promptly refrigerating soy milk after opening.
Other frequently asked questions
Can you freeze soy milk?
Yes, you can safely freeze soy milk to extend its shelf life. Soy milk can generally last 6-8 months in the freezer before quality starts to decline. Make sure to leave room in the container for expansion as the soy milk freezes.
Can soy milk be left out overnight?
It’s not recommended to leave soy milk out on the counter overnight. After 4-8 hours at room temperature, bacterial growth and chemical breakdown start rapidly accelerating. The soy milk has likely spoiled by morning if left out overnight.
Does soy milk need to be refrigerated after opening?
Refrigeration is necessary after opening soy milk to slow spoilage. The enzymes, vitamins, minerals, and nutrients in soy milk create an environment conducive to microbial and chemical degradation at room temperature. Refrigeration helps prolong its shelf life significantly.
Can soy milk be reheated after refrigeration?
Yes, it’s safe to reheat refrigerated soy milk after it has been stored properly. Bring it slowly just to a simmer, stirring often. Do not boil or overheat soy milk. Reheating helps improve the flavor of chilled soy milk.
Can spoiled soy milk be used for baking or cooking?
It’s not recommended to use spoiled soy milk in recipes. The off flavors and bacteria can impact the finished dish. Stick to using fresh, refrigerated soy milk within 5-7 days of opening for the best results.
The bottom line
Soy milk does require refrigeration after opening and will spoil if left unrefrigerated for too long. Signs of spoiled soy milk include changes in appearance, texture, smell, and flavor. Consuming truly spoiled soy milk can cause stomach upset, but serious illness is unlikely.
To maximize the shelf life of soy milk, keep it sealed and properly refrigerated below 40°F (4°C) at all times. Look for signs of spoilage before drinking, and discard any soy milk that is past its prime. Following proper storage methods will keep soy milk fresh and safe to enjoy.
