How to Tell If Yogurt Has Gone Bad

Simon King
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How Is Yogurt Made?

Yogurt is a tasty dairy product. It is usually made from cow’s milk, but it can also be made from the milk of water buffalos, goats, sheep, and other animals.

The main ingredient in yogurt is usually live and active bacterial cultures responsible for the tangy, slightly sour taste. There are about 800 types of bacteria involved in the fermentation process.

In order to make yogurt, fresh milk is first heated to a temperature of between 145-170 degrees Fahrenheit. This raises the milk’s acidity levels. The milk is removed from the heat and allowed to cool to about 115 degrees Fahrenheit.

At this temperature, which is close to blood temperature, the milk is mixed with a culture of live bacteria, often in the form of powder. The bacteria starts breaking down the milk's natural lactose sugar.

As that happens, the metabolism of the bacteria causes a slight increase in the temperature of the milk. If the temperature rises above 115 degrees, the bacteria will begin to die. The sugar that is left after the breakdown is called lactic acid.

The ideal temperature for the bacteria is 90 degrees Fahrenheit.

After ca. 6 hours, the milk is put into containers for the fermentation process to finish.

When Is It Time to Chuck the Yogurt Out?

At some point, we’ve all found ourselves relaxing on a Sunday afternoon, opening a container of yogurt and then realizing that maybe it sat in the refrigerator a little too long. So how long do you let it go before you throw it out? How does the level of dairy fat from which the yogurt is made impact the foods shelf life?

If you've looked at the list of ingredients or the label and it says "yogurt" you have to be careful. It could mean that the yogurt is made from dairy products that are very low in fat, such as milk or sour cream, and has been thickened with gelatin or pectin (both of which can be derived from bacteria organisms) to hold it's shape. Yogurt is actually the name for whole milk that is fermented with bacteria. It's typically sold with about 4% of the milk’s remaining water removed. The fat content of the original milk is what determines how long yogurt will last. Fat inhibits the growth of spoilage and pathogenic bacteria unless the yogurt is very acidic. So the less fat it has, the longer it will last.

Expiration Date

Most containers of yogurt will carry an expiration date, but it is important to note that this is an industry standard guideline only and yogurt will likely be safe to consume after the expiration date has passed. For best results, check for any of the following characteristics as a sign that the yogurt may have gone bad.

Examine containers of yogurt for signs of growth or spoilage, such as mold, bulging lids, or an acidic odor.

Check the consistency of the yogurt as signs of spoilage would be clumpy or curdled yogurt.

Once opened, use a clean utensil (such as a spoon) to dig down to the bottom of the container to ensure that it is still a consistent, uniform color.

If there is any sign of mold growing inside the container of yogurt, the yogurt should be thrown away immediately due to the risk of spoilage.

Take a Sniff

It’s usually easy to tell when yogurt has expired. Yogurt can often turn sour. It’s a process called cheese making, and it is the natural state of yogurt when it has been fermented for too long. A sour smell and taste is your first indication that yogurt has gone bad.

Beyond that, yogurt can also develop a slimy layer on top known as the pellicle, which may be caused by the microbes normally present on the surface of the yogurt. A yogurt that produces off colors over time is also a clear indication that it’s gone bad. If the color of the yogurt ranges from green to brown, it may be contaminated with mold, which is a serious threat to the health of your family.

Give It a Whirl

First and foremost, you want to check to see if yogurt is bad. If you are a frequent consumer or have a large family, it can be hard to tell when a container of yogurt is about to go bad. Fortunately, there is a test you can perform that will tell you when it’s time to throw it away.

To test, open the jar or container and make sure the lid is on securely. Next, invert it and give the jar a quarter turn. The yogurt will be pulled into one side of the container. If the yogurt is good, it will turn into the same consistency that it was prior to opening. If it continues to remain thick and clumpy, it is not good.

If it has gotten too bad, you will be able to tell if your yogurt has gone bad. It will have a sour smell to it. It may also appear moldy if it had been sitting too long. If your yogurt is left uneaten for too long, you will need to throw it out.

This test is a good way to make sure you can eat the yogurt whenever it is convenient and you don’t have to worry about if it is bad. If you find it lasts longer than the date on the container, you are set.

Put a Shade Card to Use

A shade card is used to assist lighting design and will usually include a number for each shade of grey. A shade card is made of a thin card covered in plastic, which has been specially treated to turn greys darker as you go from left to right, as you would turn the pages of a book.

With a shade card, you can choose the right paint color for any room in your home. Artificially lighting a room can change its appearance dramatically. So you need to paint the room, selecting a paint color that is suitable for the new surroundings.

Place the shade card at the focal point of the room and see how the shadows change as the light fades. The color of paint that is cast on the card is a good indicator of the color that should be used on interior walls.

This chart shows how to find the right color by placing the chart at the focal point in your room.

How to Prevent Your Yogurt from Going Bad?

What do you do with the yogurt that you’ve made to find out it’s bitter and then you need to throw it away? How can you be sure that this will never happen again?

Well, first of all, it helps to know why it happened. Regardless of what you think, it’s not because of using the wrong method. As strange as it sounds, your yogurt went bad because you used the correct method.

Science has this rule called “Osmosis”. It means that liquids will move from an area of low concentration to an area of high concentration. So to get yogurt with good taste, you have to have live cultures. Those live cultures are in the yogurt you just tasted bad.

But what if those are gone? Maybe, you’ll just have a spoonmeat with no taste or maybe, it’s completely plain.

When you’ve noticed that something is wrong with the taste, don’t make a fuss. Simply warm up the yogurt in the microwave or add honey or fruit to it to see if you can still eat it.

Final Thoughts

Using the refrigerator temperatures will keep your yogurt fresh for a few days. You can also keep it in your freezer; it will keep even longer.

Most important of all, though, is to avoid over-storing anything. That is the surest way to get rid of that great taste.

You will want to follow the shelf life as closely as possible, but it's better to eat the yogurt quickly because it's too good to let it go to waste.