0 Is My Homemade Yogurt Safe to Eat?

Yogurt with Lemon Curd & Blueberries

It's simply magical to take fresh milk, add a couple tablespoons of fresh yogurt, pour them into a yogurt maker, and Voila! Several hours later, you have the most incredible yogurt that you have ever tasted. Making yogurt is now even easier with cookers designed to keep this mixture at a constant temperature, resulting in perfectly cultured yogurt that is safe to enjoy. 

But what happens when something goes wrong? 

Homemade yogurt should look like this:

Homemade Yogurt should NOT look like this:

"I overslept and forgot about my yogurt. It's been sitting in the cooker for several hours,"
"After eight hours, my yogurt still looks milky thin," 
"My yogurt looks watery and curdled. What did I do wrong?" 
"Can I use this in smoothies or start over?" 

"Is my yogurt safe to eat?"

There can be many reasons why your yogurt didn't turn out. This article will focus on food safety, common myths and what to do if you are not sure if your yogurt cultured successfully. You can find more troubleshooting help in my Instant Pot Yogurt for Newbies Guide and in my Instant Pot Yogurt 101 Facebook group

Food Safety

I consulted with  food safety and yogurt experts who are more knowledgeable for troubleshooting guidance while I was teaching and writing about yogurt.  Cultures for Health, Brod & Taylor, and other reputable sources are listed at the end of this article. 

Fact: Dairy products should be kept at temperatures below 40°F. Refrigeration slows down the growth of most, but not all bacteria. Food left out at room temperature for two hours or more can rapidly grow bacteria that can be harmful. (source)(source)

Fact: Yogurt made in cookers with the yogurt setting culture in the 100°-110°F temperature range. The starter added to the milk needs to be actively culturing the yogurt to be safe for consumption. (source)

When in Doubt, Throw it Out 

Time, Look, Smell & Taste
How do we know if yogurt is safe to eat? Milk that has sat out at room temperature for several hours will develop signs of spoilage: curdled consistency, sour odor, and an off-flavor. We can use the same test for yogurt: Time, appearance, smell & taste. If your yogurt fails the test for ANY of these, it needs to be discarded.

Time - Yogurt should be cultured by 8 hours
Yogurt takes at least 8 hours to culture and some ultra pasteurized milks take even longer; at least 10-12 hours. 
Fact: When the yogurt cycle is done, the cooker turns OFF.
Fact: The temperature of your yogurt will drop and two hours later, will be 90°F or lower. 
Fact: Yogurt is a perishable food and should be refrigerated within 2 hours after the incubation cycle is done. (source)
Bottom Line: If yogurt has been sitting in a cooker that has been off for two hours or longer, it should be thrown out, even if it looks and smells like yogurt.

TIP: Set an alarm to check your yogurt so you don't forget about it. 

Would you leave milk sitting out at room temperature for several hours and still drink it? 

Still milky at 8 hours? 
Tip your pot slightly. If you see thickening near the bottom, add 1-2 hours more incubation time. Reset your yogurt incubation setting and add at least 2 hours.
Note: Organic milks need to incubate at least 10-12 hours. Plant based milks need to incubate at least 12-15 hours. 
Still milky at 10 hours? 
You'll need to toss it out, as you have essentially had milk in warm temperatures without an active starter to culture it into yogurt. (
*Exception* Plant based milks need a much longer time to incubate, at least 12 hours. If gelatin is used, yogurt will look thin, but set up when chilled in the fridge, like Jello.)
Bottom Line: Milky yogurt is evidence that your starter did not work. Your starter needs to contain live & active bacteria to culture your yogurt properly. Do not use milky thin yogurt in smoothies or try to reculture it. 

TIP: Always use fresh milk & yogurt starter that contains live & active cultures. Use only the recommended amount of starter in the recipe. 

Look -Yogurt should look cultured, or set. 
This means your yogurt should look semi set or firm like a Jello pudding. (see pics above)
The surface of your yogurt can be smooth or have air bubbles from whisking your ingredients. 
Plant based milks can have cracks on the surface. There may be droplets of condensation or pools of whey on the surface. This is normal
How to Check: Tip your pot slightly to the side. Yogurt should pull away from the sides of the pot. 
Take a spoonful of your yogurt. It should not run off the spoon. Do not stir!
*SPOON TEST* Pictures of spoons standing in the middle of yogurt are when whole fat, high protein milks are used and are most commonly taken AFTER chilling. 
Bottom Line: Some spoons are heavier than others and may fall to the side of warm yogurt, especially if you are using low fat milk.  This is okay! Properly cultured yogurt will firm up when fully chilled enough to take a spoonful. 

Not all spoons stand up in successful yogurt

Yogurt should NOT look milky, runny, lumpy, slimy, stringy, gluey,  or curdled. 

Color: Yogurt should look like the color of the milk or creamers added to it. 
A creamy yellow color on top is normal when heavy cream is added to the milk.  The cream rises to the top during incubation and can form a crust. You can scrape this off, spread it on toast or stir it into your yogurt. 
While rare, any fuzz or pink spots on the surface of yogurt are an indication of mold and should be discarded.
Smell: Yogurt should have a fresh, pleasant, fermented smell. It can smell sour, but should not be pungent (strong or sharp).  
If it smells rancid, foul, spoiled, strongly acidic, rotten, or off-putting, something other than yogurt bacteria has cultured and it should be thrown out. 

Taste: Yogurt should taste pleasant. It can be mild or tangy. Unsweetened yogurt will taste plain and may taste sour, like sour cream. 
It should not taste overly sour, acidic, rancid, or "off." If it does, it should be discarded.

Debunking Myths 
Not everyone understands the science or food safety of yogurt. These are common myths about failed yogurt or yogurt sitting out for several hours:
I ate it and nobody got sick or died
Fact: Not everyone has an iron stomach. You can get sick consuming food with unknown bacteria. Those with immune compromised systems could get very ill. (cramps, diarrhea, vomiting)(source)
Fact: If it doesn't look like yogurt or smell like yogurt, this means the balance of bacteria is OFF. Even if yogurt looks like yogurt after sitting at room temperature for several hours, it can harbor unknown bacteria that may make you sick. (source)

Yogurt has been made for centuries at room temperature. 
Fact: Cultures used back then were mesophilic bacteria that cultured at lower temps of 77°F-90°F. 
Fact: Store bought yogurt contains thermophilic bacteria.
Thermophilic yogurt cultures best in the 100°F-110°F range. They do not grow well at temps below 98°F. (source)
Fact: When the temperature of thermophilic yogurt drops below 90°F, other unknown bacteria can grow, changing the tang, texture and safety of your yogurt. 
Yogurt is fine up to 24 hours, it'll just be more tangy
Fact: it's fine if you intentionally set your cooker to incubate for up to 24 hours. Longer incubation times create more tang & whey separation.
Fact: Instant Pot and other yogurt cookers turn OFF after the cycle ends.  
After 2 hours, the yogurt temperature drops to 90°F or lower and continues to drop the longer it sits out, allowing unknown bacteria to culture and grow. 

I strain my yogurt at room temperature for several hours. Is this safe?
Fact: It is recommended to strain your yogurt in the fridge. You can strain your yogurt at room temperature as long as it is under two hours, then put into the fridge to chill.  The longer your yogurt is at room temperature, the more likely unknown bacteria will grow in it.

You can just add more starter and incubate again.
Fact: Milky thin yogurt at the end of 8-10 hours means that your starter hasn't been actively working to culture your milk into yogurt.  
Fact: Your milk has been sitting at unsafe food temps for several hours without an active yogurt to culture it. Your milk will have unknown bacteria that have been growing for several hours. This unknown colony of bacterial strains can make you ill if consumed.
Fact:  Adding more starter will not work well as it will be competing with all the bacteria that has grown in the milk. 
Exception: Organic milks and non dairy milks can take longer to culture, at least 10-12 for dairy and 12-15 for non dairy. You should see some evidence of thickening near the bottom of the pot by the 10th hour. You can check for this by tipping your pot slightly and looking down into the bottom of your cooker.  

You can reheat the milk to 180°F and start over again. 
Fact: your milk has an acid (yogurt used as starter) and reheating it will only cause it to curdle, changing its texture and taste. 
Fact: There is still unknown bacteria in the milk, even if you heat it to 180°F. To kill all the bacteria that can compete with your yogurt starter, you'd have to heat milk to 280°F. Heating milk too hot, too quickly can make your yogurt grainy or gritty. Best to start over with new ingredients.
Yogurt with nuts & berries

Keeping Homemade Yogurt Safe to Enjoy

Store your yogurt in food safe plastic or glass containers that have a well fitting lid, in the coldest part of your fridge. (40°F) You can use one large container or divide your yogurt among smaller, individual sized containers. 

Refrigeration: Yogurt should be put in the fridge as soon as it is finished incubating. 
Shelf life of refrigerated yogurt: 2-3 weeks. 
Yogurt with any signs curdling or microbial growth (mold) or unpleasant smell should be discarded immediately. 
It is normal for yogurt to develop whey (greenish-yellow liquid) on the surface while in the fridge. This whey can be poured off, wicked up with a paper towel, or simply stirred into the yogurt. 
Freezing: You can freeze your yogurt as starters for future batches of yogurt, popsicles or turn it into ice cream. Thawed yogurt separates, loses its creamy texture and while edible, I prefer to enjoy my yogurt fresh. 
Shelf life of frozen yogurt: 3-6 months. 

How Long Can Yogurt Sit Out? Undeniably Dairy, 3-7-2017
Food Safety During Power Outage FoodSafety.gov, 1-28-21
Yogurt, an Excerpt from 'The Art of Fermentation' , The Splendid Table, July 24, 2013


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