What Is the Importance of Lactic Acid in Yogurt Making? 

 August 13, 2021

By  Diane Miles

For people who are interested or already make yogurt at home, you’ve probably already come across lactic acid during your research. However, many still aren’t sure what the role is of lactic acid when it comes to making yogurt.

Lactic acid causes the milk to thicken and develop a tart taste as it ferments, because it decreases the pH levels. In addition, it also makes yogurt easier to digest and allows it to be stored for a longer period of time because it changes the texture of the proteins.

There are many things to know about lactic acid and its role in yogurt making. Read on below to learn more.

What Does Lactic Acid Do in Yogurt?

Yogurt is the most popular fermented dairy food product in the world, and it’s made using any kind of milk following a simple process:

  • Heat the milk;
  • Add in a bacteria source, which acts as a yogurt starter or mother culture (Lactobacillus bulgaricus or Streptococcus thermophilus are the two most commonly used bacteria species in yogurt);
  • Allow the milk to incubate for 6-8 hours.

Yogurt Making Chemistry

As the milk incubates, it undergoes a fermentation process. The bacteria ferments the lactose, which refers to the milk sugars, and forms lactic acid. The presence of lactic acid is beneficial in reducing the pH levels of milk, making it more acidic and resulting in the coagulation of proteins.

Yogurt usually has an acidity level of pH4, though the more lactic acid is produced during fermentation, the more tangy the yogurt will taste. Though lactic acid contributes to the tart taste of yogurt, its final consistency and taste can also be influenced by adjusting the type of starter used, as well as the length of incubation.

It’s also good to note that while lactic acid bacteria, such as Streptococcus thermophilus can grow the lactic acid independently, it grows significantly faster when milk is present. This process is known as protocooperation.

How Much Lactic Acid Is in Yogurt?

When yogurt is incubated for 2.5 hours in 43 degrees Celsius, the acidity results in pH levels of around 4.2. In determining how much lactic acid yogurt has, Dornic degrees, or acidity measure, is used. For example, raw milk has 1 Dornic degree, equivalent to 0.1g of lactic acid for every liter.


Lacto refers to the use of lactic acid, which is an acid that is formed when sugar is broken down in an environment that does not have any oxygen. Since lactic acid was first discovered in milk, which has lactose, this is why it was named lactic acid.

The process of lacto-fermentation involves using lactic-acid producing bacteria to break down sugar and form lactic acid in food. Aside from yogurt, lacto-fermentation is widely used in foods from all over the world such as kimchi, pickled cucumber and other pickled vegetables, sauerkraut, olives, sourdough bread, meats, and much more.

However, lactic acid bacteria is already present in nature. When it’s available in milk, vegetables, and grains, these can be used for fermentation. But special cultures such as those used for yogurt can also be added in order to begin the fermentation process. It’s especially helpful for food that doesn’t have naturally occurring populations of beneficial bacteria, which helps promote flavors or help ensure that it’s safe to eat.

A tightly sealed container is usually used in lacto-fermentation to keep the oxygen out, which is why yogurt is made with food-grade containers or specially designed glass jars attached to a machine. When bacteria breaks down the sugar, lactic acid is formed, which removes the oxygen and helps turn up the acidity which in turn spawns the growth of added lactic acid bacteria while inhibiting the growth of other microorganisms.

Why Is Lactic Acid Beneficial in Yogurt?

The use of lactic acid in fermentation helps food stay fresher for longer; this is why yogurt, when refrigerated, can be stored for up to a month. It’s also the same reason why fermented vegetables last for 4 months or even more. Additionally, fermentation makes yogurt and other foods so much easier to digest. It eliminates the need to cook while adding specific flavors and aromas.

Health Benefits

There is strong evidence that the lacto-fermentation process yields distinct health benefits because of lactic acid. These include:

  • Reduce cholesterol levels and improve heart health
  • Reduce inflammation
  • Improved nutrient absorption
  • Weight control
  • Improved blood sugar levels
  • Reduce risk of cancer

So while lacto-fermentation was originally developed to increase shelf life of foods, it also plays an important role in starting the fermentation process in yogurt to make it easier to digest while offering extra health benefits.

What are lactic cultures in yogurt?

Lactic cultures, or lactic acid bacteria, refers to a microscopic bacteria that helps start the fermentation process in yogurt. These are the components of commercial starter cultures, the most common of which are the probiotics belonging to the Lactobacillus and Bifidobacterium genuses.

However, the Lactococcus and Streptococcus species are also popular. When shopping around for lactic cultures, you’ll notice they contain millions of probiotic bacteria which help ferment the milk as long as you follow the procedure correctly.

There are some things to keep in mind when selecting  and using a lactic culture to use for making homemade yogurt:


Single-Use Cultures: Single-use, or direct-set cultures, are added to milk to make just one batch of yogurt. If you are a seasoned yogurt maker, you can re-culture single-use culture up to three times when using some of the yogurt as your starter when creating a new batch.

Reusable cultures: Reusable or heirloom cultures can be re-cultured indefinitely. Each batch of yogurt can be reused time and again to make more yogurt. Keep in mind that heirloom cultures must be propagated once every week to keep the vitality of the bacteria.


Only add the lactic culture to the milk when the temperature is below 42 degrees Celsius. If the temperature is above this, it will kill the bacteria, since they are extremely heat sensitive.

You can also purchase starter cultures that are formulated to give certain flavors and textures of yogurt, depending on your own preferences.

Lactic Acid Starter Culture Examples

Making homemade yogurt is easy when you have lactic acid cultures. Here are some high-quality starters that are available on Amazon:

-   EuroCuisine All Natural Yogurt Culture
-   Yo Gourmet Freeze Dried Yogurt Starter
-   Cultures for Health Vegan Yogurt Starter

Frequently Asked Questions 

What are the benefits of lactic acid in yogurt for the skin? 

Lactic acid is already widely used in many skin care products as well as professional skin treatments. Since it’s produced through fermentation in yogurt, your skin can enjoy numerous health benefits when you consume yogurt. However, there are many women who use yogurt topically for aesthetic purposes:

  • Natural exfoliation: Lactic acid helps remove old skin cells found on the skin’s surface. It also stimulates cell renewal and speeds up the turnover of old to new cells.
  • Brightens complexion: Regular exfoliation leads to brighter skin, and that’s what lactic acid can do.

On top of that, lactic acid is also a type of alpha hydroxy acid (AHA), which are overall known for improving skin texture and moisture. Using lactic acid on a regular basis, whether by applying yogurt directly on your skin, eating it, or using other AHA skin care products, has been known to reduce the signs of aging, such as age and sun spots, fine lines, and wrinkles.

Lactic acid is also the main ingredient found in many over-the-counter creams used to treat keratosis pilaris, the medical term for chicken bumps that are commonly found in the back of arms, in armpits, and on the butt. In addition, lactic acid is used in treatments made for psoriasis, eczema, and rosacea.

However, it’s always best to get a clearance from your physician or dermatologist before adding it to your skin care routine. There are some side effects from using lactic acid topically even if it’s gentle:

  • It can increase sun sensitivity
  • It may cause skin irritation
  • It can’t be used together with topical retinoids such as Retin-A

So despite the good track record of lactic acid for the skin, and its incredible popularity as a treatment, always talk to your doctor first before deciding to use it for yourself.

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