Should Yogurt Taste Sour Or Has It Gone Bad?

Yogurt and making yogurt is a common activity among homesteaders and preppers. For beginners to this activity, there may be some grey areas where you are not sure whether your yogurt has gone bad or whether it is still good to eat.

Yogurt is a cultured dairy product that is supposed to taste sour or tart. A sour taste in yogurt is different from the sour taste in milk when it begins to go off. There are other indicators that will let you know if your yogurt has gone bad or whether it is still good to eat.

Making yogurt as a homesteader is a very common practice, and there are many different methods and recipes to get yogurt, but essentially the basic principles are the same. There are some basic guidelines that need to be adhered to when making yogurt to make sure it stays good to eat in your refrigerator instead of causing illness!

How Is Yogurt Made?

To understand the taste of homemade yogurt, it would be helpful to be familiar with the process of how it is made. This will give you a baseline standard from which your taste buds and nose can guide you as to whether your yogurt has gone bad or not.

Yogurt is made from cows milk and can be made from full-fat milk or low-fat milk, as long as the lactose content of the milk has not been altered. I have never tried to make yogurt with fat-free or skim milk, so I can’t give any advice on how the yogurt will turn out with this type of milk.

Yogurt is a cultured dairy product, which is produced by introducing micro-organisms into the milk, which cause a chemical change in the milk and essentially produce yogurt.

The micro-organism used is a bacteria family called lactobacilli, which essentially feeds on the sugar or lactose in the milk. The bacteria convert the lactose into an acid called lactic acid, which is what gives the yogurt its tart or sour taste.

The acid acts on the proteins in the milk and causes it to thicken and become creamy. The time taken for this fermentation process to occur is temperature-dependent. The warmer the temperature, the faster the process, and the cooler the temperature, the slower the process will happen.

In commercial yogurts, once the bacteria have converted a sufficient amount of the lactose to lactic acid to produce a specific flavor, the bacteria are killed off to increase the shelf-life of the product. Unfortunately, this also denies the consumer of commercial yogurt the beneficial live culture bacteria, which help to improve gut health.

In homemade yogurts, the fermentation process is slowed down by placing the yogurt in the refrigerator, which slows the process down, but does not halt it completely, and does not destroy the bacteria. As a result, homemade yogurts are usually better for your gut health than store-bought equivalents.

Why Are Some Yogurts More Sour Than Others?

Yogurts are usually cultured at room temperature because this level of temperature is more conducive to the active reproduction of the bacteria and thus the fermentation of the milk into yogurt.

In homemade yogurt, once the yogurt reaches its required tartness according to your preference, the yogurt can be placed in the fridge in a sealed container to slow down the culture process. This does not halt the process but only slows it down. This means that your homemade yogurt will continue to become more and more tart, or sour, even in the fridge. The process will just happen at a slower rate than it would at room temperature.

As a result, if your yogurt lasts a few days in the fridge before you consume it, it will taste more tart or sour than when you first put it in the fridge. Our homemade yogurt does not last long enough in the fridge to get to the point where it becomes too tart for our taste; it is eaten way before that happens!

Commercial yogurt will not continue to culture in your fridge since the culture bacteria have all been destroyed to extend the shelf-life of the product. In commercial yogurts, plain yogurt will taste more sour than flavored yogurts because sugar is added to any commercial yogurt that has fruit or flavoring added to it. The added sugar reduces the sour taste of the yogurt.

How To Know If Your Yogurt Has Gone Bad?

It is certainly possible for yogurt, both homemade and commercial, to go bad. So what are the tel-tale signs that your yogurt is starting to get to the point where you should not consume it?

Good yogurt has a clean, fresh taste and smell. Even though the flavor is sour, it is not the same type of sour as milk that has gone bad. Milk that has gone bad has an offensive smell that makes you not want to consume it. Basically, the proteins have started to break down, and the milk has started to rot.

Yogurt is a fermented culture that uses specific bacteria, which is not the same bacteria that cause rotting or degradation and causes dairy products to go bad.

When yogurt goes bad, it loses its clean, fresh taste and begins to taste musty. Soon after this, it will start to develop yeasts and molds that will grow on the surface of the yogurt, and they will be visible to the eye. The mold can be white in color but will form a type of crust on the surface.

Your nose will also tell you that it is not good to eat. The smell will be a more rotten milk type of smell rather than the clean, fresh smell of yogurt. When you smell this, you will know that this is not something you want to put into your mouth.

How Should Yogurt Last?

Homemade yogurt will last at least seven days in your fridge but can last up to fourteen days. You should take care to not double-dip with a spoon in your yogurt. Do not taste the yogurt with a spoon and then put the same spoon from your mouth into the yogurt again. Rather dish up some of the yogurt into a bowl from which you can eat. Double-dipping will introduce additional bacteria or bad bacteria from your mouth into the yogurt and can cause it to go bad.

Commercial yogurt will have a longer shelf-life in your fridge if it is unopened. However, when opened, it will have about the same lifespan in your fridge as homemade yogurt. This is because it will be exposed to the same air and potential contaminants as anything else in your fridge.

Commercial yogurt can spoil in the same way as homemade yogurt, so the same precautions should be taken with both products in your fridge.

Why Do People Make Their own Yogurt?

Making your own yogurt is a homesteading skill that many people try, each with their own reasons for doing so. For some people, it is a method of using excess milk that their livestock produce, while for others, it is to produce a healthier alternative to a store-bought product.

The active bacteria in homemade yogurts are what is termed good bacteria and are beneficial in creating and maintaining a healthy environment in your gut. A healthy gut can have many health benefits for people, including boosting the immune system and thus assisting your body to fight off infection and disease.


Yogurt tasting sour is not necessarily an indication that the yogurt has gone bad. Yogurt has a naturally sour taste due to the lactose that is converted to acid during the culture process.

Yogurt that has gone bad will smell bad to the point of being offensive and will be an indication that you should not eat the yogurt.

Any sign of mold or yeast growth on the surface is also an indication that the yogurt should be discarded and not consumed.

Yogurt, especially fresh homemade yogurt, can sometimes start to separate and get a watery liquid on top of the surface of the yogurt. This is not a sign of the yogurt going off but is a natural separation of the whey from the yogurt. This watery liquid can simply be stirred back into the yogurt, or if you prefer, poured off from the yogurt. The yogurt is still, however, good to eat.

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