How long can sealed yogurt be unrefrigerated?
In this brief guide, we are going to answer the question “How long can sealed yogurt be unrefrigerated?”, and discuss other questions like how to store the yogurt, and how to know if your yogurt is good to eat or not.
How long can sealed yogurt be unrefrigerated?
You can keep your yogurt unrefrigerated for 2 hours , after that, it can start to undergo undesirable alterations and be no longer safe to consume.
If the room temperature is 30°C or higher, unwanted alterations can occur even faster, and that two-hour window is shortened to one hour. This applies to all forms of yogurt.
Yogurt generally is acidic and is not spoiled by most bacteria. The acid also restricts the growth of most food-poisoning bacteria. The high acidity makes yeast the major spoilage organisms of yogurt, together with molds .
Upon temperatures between 4-60°C, microbes’ growth takes place at a faster pace . Therefore, yogurt should be refrigerated at 4°C to achieve a shelf life of 7 to 14 days, otherwise, it will spoil and become unsafe.
What are the risks of leaving yogurt unrefrigerated for too long?
Some people might say they keep their yogurt unrefrigerated for 6-8 hours mostly when they bring it to work and it tastes good. Indeed, yogurt going bad depends on temperature and other factors like acidity, and sugar content.
Additionally, the high acidity of yogurt inhibits the growth of most harmful bacteria. But, we would recommend you refrigerate yogurt within two hours. It may not taste bad, but still, there might be spoilage that you can not see.
According to Bozoglu , two harmful bacteria, namely Escherichia coli O157:H7 and some strains of Listeria monocytogenes are able to survive or adapt to acidity and remain in yogurt during the storage period.
These microorganisms can cause diarrhea, stomach cramps, vomiting and even death.
Recent outbreaks involving Greek yogurt contaminated with E.coli O157:H7 have been reported . Sixteen people were affected, among them, some children.
Related symptoms included severe stomach cramps, bloody diarrhea, fever, and, in severe cases, kidney failure complication .
In another recent product recall, a blueberry yogurt was detected contaminated with molds. Although no confirmed illnesses had been reported, molds can produce toxins that pose a risk to human health [2,3].
We can say that cases like those are not usual in the dairy industry, but you never know when they could happen. Thus, it is better not to take the risk and protect yourself from unpleasant surprises with your yogurt.
Besides safety issues, the quality of the yogurt can be damaged, as the yogurt bacteria continue to produce acids, which are boosted by high temperatures, causing an objectionable sharp acid taste .
Bozoglu  also stated that some spoilage yeast species, such as Rhodotorula glutinis, Yarrowia lipolytica, may cause quality problems in yogurt stored at relatively higher temperatures (such as 15–20 °C).
How to know if your yogurt is good to eat or not?
Yes, you can decide if your yogurt is good to eat or not just by looking for some signs. Let’s find out what are those changes that indicate the yogurt has gone bad.
1. Too acidic taste
If you feel your yogurt is more acidic than normal, this can be the result of bacteria in yogurt continuing to produce acid. Bacillus is the predominant type of spoilage bacterium in yogurt, followed by Lactobacillus, Streptococcus, and Actinomyces .
When leaving your yogurt unrefrigerated, these microorganisms multiply faster. But they are not harmful to your health. In this case, your yogurt is still safe to consume, it just does not taste as good as before.
2. Detection of off-flavors and off-odors
Yeasty, fermented, or fruity off-flavors are the result of yeast growth, the main spoilage microorganism in yogurts . If you are able to detect these signs this indicates a high contamination by yeasts.
The most common yeast spoilage is caused by S. cerevisiae (the same one used to produce beer, bread, and wine). Higher temperatures stimulate the growth of yeasts.
It is advisable to discard the yogurt if you find it like this.
3. Presence of gas
A gassy appearance shows up due to the production of gas (carbon dioxide) by yeasts . It is advisable to discard the yogurt if you find it like this.
4. Presence of molds
The molds can grow on the surface of yogurts stored for a longer time. When you open a container and you see green, off-white, black growth on the yogurt surface it is mold. It will kill all the good bacteria and will have a foul smell.
You should immediately discard the yogurt container.
5. Color change
According to Bozoglu , the growth of yeasts and molds in yogurt causes heterogeneous color distribution on the surface of yogurt, particularly when stored at higher temperatures than recommended.
If you notice any color change in your yogurt, discard it.
How to store your yogurt?
· Store your yogurt in the refrigerator at 4°C. Unopened it will last for 7 to 14 days. After opening, it lasts for about 2 days.
While in the refrigerator, keep the yogurt well sealed. This will avoid contamination and the yogurt pick up odors from the surrounding.
· If you do not wish to finish the whole yogurt container at once then make sure to use a different spoon and not one you are eating with. Take out the portion on a plate, seal the container, and keep it back in the fridge.
For liquid yogurts, take a serving in a glass and do not drink directly from the bottle top, it will bring contamination to the remaining content in the bottle.
· While making yogurt at home, always use pasteurized milk. Make sure to sanitize all the utensils you use, to avoid the addition of unwanted bacteria.
· If you leave your yogurt out by mistake make sure to refrigerate it within 2 hours.
Frozen yogurt can have a shelf life of 1 to 2 months. But may lose texture and color after thawing.
In this brief guide, we answered the question “How long can sealed yogurt be unrefrigerated?”, and discussed other questions like how to store the yogurt, and how to know if your yogurt is good to eat or not.
2. (2016). Spoilage of Milk and Milk Products. In Food Microbiology: Principles into Practice (eds O. Erkmen and T.F. Bozoglu)