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When Good Cultures Go Bad. Is Yogurt Safe When Left Out?

Posted in Food Safety,Our Blog,Outbreaks & Recalls on February 21, 2019

Yogurt.  Mmmm…  That tangy, sour, versatile treat.  Have it as a snack paired with fruit, jelly, nuts, honey, candy, or anything your heart desires.  I fall somewhere between healthy honey drizzled Greek yogurt and what we fondly call “dirt pudding” with crushed Oreo’s and garnished with gummy worms.  Have you ever, in your hurriedness to enjoy the snack, forgot to put the yogurt back in the refrigerator only to find it an hour or so later?  <Sheepishly raises hand>  I have.  As I stared at the container when I finally returned to it, I contemplated.  Can it really go bad?  I mean, I know there is an expiration date on it and all.  But it is essentially sour milk.  Does it get more sour?  Will it make me sick?  Is Yogurt Safe When Left Out? Let’s explore this topic.

First, what exactly is yogurt?

Yogurt – A Culture with Culture

The word itself comes from Turkey.  It means something along the lines of tart, thick milk.  But all yogurt did not come directly from Turkish descendants.  Nope.  Essentially every culture that has kept animals for milk ended up discovering yogurt in quite similar ways despite the region they lived in.

How is it made?  Yogurt is born from combining “friendly bacteria” with fresh milk and giving it time to marry.  As the bacteria consume the milk, the substance thickens and develops a beautiful tart and slightly acidic taste.  Part of this tartness comes from lactic acid.  This lactic acid is produced during the fermentation process and acts as a sort of preservative.  This pH shift and natural preservative helps the cultured milk product stay fresh longer.

Many cultures found that “culturing” milk extended the shelf life of the product, reducing waste and creating a new way to enjoy their dairy animals.  Yogurt, like salted meat and pickled vegetables, helps keep nutrient rich foods around during times of limited resource availability.

What’s in a Name?

While different regions ended up using various types of friendly bacteria, all achieving the same end result – albeit with slight variations in taste and texture, they are all essentially the same product.  So do we call them all yogurt?

Not quite.  Much like champagne must be made in the Champagne region of France or it must be called “sparkling wine” or Scotch whisky must be made in Scotland following a specific set of rules otherwise it is just “whisky,” the FDA has given yogurt its own rules, though I believe these only apply in the United States.

The United States Food and Drug Administration (FDA) defined yogurt in 1981, stating that “it must include Lactobacillus bulgaricus and Streptococcus thermophilus.

Are there other beneficial bacterial strains that could make yogurt?  Absolutely!  But according to US law the products made with them can’t be labeled and sold as “yogurt.”  The compromise is that they may be called “yogurts.”

Back to my poor neglected quart of yogurt sitting on the warm kitchen counter…

What to Do About My Abandoned Yogurt?

Yogurt should be stored in the refrigerator at 40 ºF or below.  But what happens when it gets outside of the refrigerator? is a great resource on temperature charts and food handling.  They say that dairy products such as “milk, cream, sour cream, buttermilk, evaporated milk, yogurt, eggnog, and soy milk” that is “held above 40 ºF for over 2 hours” should be discarded.  If your kitchen gets up to 95 ºF drop that timeline to just 1 hour.

How Do I Know if My Yogurt is Bad?

So now we know that yogurt can go bad, despite it already being sour.  And we know that we’ve got somewhere between 1 to 2 hours outside of the fridge before we have to toss it.  But how can I tell by looking at it if I should throw it out?

Well.  There is a whey.  You didn’t read that wrong.  Whey.  The whey is the little bit of liquid that settles on the top of some yogurts.  Many are tempted to drain that liquid out and avoid it, but it is packed with lots of protein and nutrients.  Don’t say no way to whey.  Mix it in and enjoy!

But it is this whey that can give you clues as to whether your yogurt has seen its best days and must be discarded.

If you’ve got a lot of whey, or yogurt that doesn’t normally form whey on the surfaces starts to  produce that large puddle on top – your yogurt could be going bad and consider throwing it out.

If you find a curdled texture at the bottom of the container or see lumps and sediments in the yogurt – your yogurt is bad, and you should throw it out.

If you find you have things growing on your yogurt, like mold or fungus – your yogurt is bad, and you should throw it out.

So, now we know when yogurt starts to go bad and when to toss it in the trash.  How can I store yogurt so that I get the most out of it?

Proper Yogurt Storage to Ensure Longer Freshness

Well.  First, don’t leave it on the kitchen counter and forget about it.  Note to self…  Aside from that, here are a few tips:

  • Store in the Refrigerator – Store your yogurt in a sealed container in the refrigerator set to 40 ºF or below. This will allow from 1 up to 2 weeks of shelf life with your yogurt.
  • If You Leave It Out – If you leave the yogurt out of the refrigerator for over 2 hours (or 1 hour if over 90 ºF) throw it out.
  • Remove Your Serving from the Container – Transfer what you wish to eat to a serving container and put the larger container back in the fridge. This will ensure that your yogurt stays refrigerated and avoids introducing bacteria from your mouth if you are eating out of the large container.
  • You Can Store Yogurt in the Freezer – Yogurt can be stored in the freezer for around 1 to 2 months. You might find your yogurt discolored after thawing.  Mix well.
  • Homemade Yogurt – If you are brave enough to ferment your own yogurt follow the directions very carefully, purchase culture from a reputable source, and ALWAYS USE PASTEURIZED MILK.


By: Heather Van Tassell, Contributing Writer (Non-Lawyer)