Probiotic Milk Test: How Do You Know Your Probiotics Are Working?

So you've just purchased a probiotic and are hoping to receive the many benefits that you've read about. Problem is, how can you be sure that the probiotic you received is going to be alive and effective.

Many people aren’t sure if their probiotic supplements are actually working and have developed a simple, at-home test to try to determine the quality and effectiveness of the probiotics. This test is simply known as the “probiotic milk test.” 

In this article we will go over the milk test and whether or not it is a good test for the viability of probiotics.

What is the Probiotic Milk Test?

The milk test is meant to imitate the yogurt production process. The milk test only requires some milk, a bowl, and your probiotic supplement.³

1. Pour 4 ounces of the cold milk into a glass. Add the probiotic capsules or powder into the milk.
2. Place the glass of milk and probiotic covered with saran wrap. The saran wrap should contact the milk as much as possible to simulate an anaerobic environment.
3. Keep the glass of milk as close as possible to 98 degress F, keeping it in sunlight if needed. 
4. After up to 24-48 hours, check the glass to see if the milk has curdled.

The test is designed to demonstrate the ability for certain probiotic bacteria to create lactic acid which curdles the proteins in the milk.

The bacteria that are typically used in yogurt production are usually

Streptococcus thermophilus and Lactobacillus bulgaricus.

The thinking is that only live probiotics would be able to ferment lactose, a sugar found in milk, to lactic acid². Therefore, seeing curdled milk would be a positive sign for probiotic activity.  

What’s Wrong with the Milk Test?

While some probiotic bacteria will cause milk to clump or curdle, it’s not an identifying trait of all probiotic bacteria. Not all probiotics will ferment lactose and produce lactic acid. The products of fermentation can include ethanol, lactate, and hydrogen gas. The ones that primarily produce lactic acid are called Lactic Acid Bacteria (LAB). 

Lactose is actually made of two 6-carbon sugars, glucose and galactose. In lactic acid fermentation these 6-carbon sugars are converted into the 3-carbon molecule lactic acid which causes the curdling of milk.

Reasons the probiotic milk test is not reliable:

1. Specific strains do not promote milk cudling.

However, if there are probiotics in your probiotic mixture that don't just make lactic acid then there will be less lactic acid produced. Less lactic acid means less milk curdling. This will be true if your probiotic contains Saccharomyces boulardii⁵ probiotic in addition to Streptococcus thermophilus and Lactobacillus bulgaricus as seen in Nexabiotic Advanced 23-strain Probiotic. Saccharomyces is a probiotic yeast that ferments sugars differently than lactic acid bacteria. 

2.There is Chymosin

Furthermore, if you do see clumping, it does not necessarily mean that probiotics are the ones causing the clumping.  Other bacteria or compounds in the milk could be doing it. For instance, more chymosin (sometimes known as rennin) is an enzyme commonly used in the production of cheese. It can also cause milk to curdle, but instead of creating lactic acid and fermenting the milk, chymosin’s mechanisms act directly on milk’s proteins.

Some probiotic products may contain chymosin as an ingredient, which can result in curdling, which does not actually prove anything about the activity or quality of the probiotic bacteria supplement.

3. Crushing of Probiotics

The milk test is also unreliable with probiotic pearls or tablets that have not been crushed. Putting whole tablets into the milk would obviously show no effects as the probiotics can’t even make it out into the milk. If you are testing a pearl or tablet be sure to grind it up before putting it into milk.

The same goes for probiotic products with enteric coatings.⁴ Enteric coatings are a delayed delivery mechanism designed to delay the release of contents until after it is exposed to the acidic contents of the stomach. If you are testing a capsule with an enteric coating it is easy to bypass for the milk test by opening the capsule. If it's an enteric coated tablet you can grind it up and put it into milk.

How to Reliably Tell if Your Probiotics are Live

The at-home milk test of probiotics ultimately cannot be relied on to gauge the effectiveness of a multi-probiotic supplement. If the probiotic only contains Streptococcus thermophilus and/or Lactobacillus bulgaricus then the milk test would work.

The only real way to determine the viability and effectiveness of a probiotic is through lab testing under controlled conditions, allowing researchers to eliminate any contaminants and to quantify the CFUs of a probiotic.

Lab tests also create more quantitative measures of effectiveness while also determining other important factors, including product purity, safety, and nutritional value, that can’t be determined by curdled milk.

Because DrFormulas™ Nexabiotic® Advanced Probiotics and Prebiotics for Women and Men features 23 different probiotic strains, you cannot rely on the milk test to quantify its strength. However, it has been third party lab tested for quality and viability, ensuring that you get the most out of your probiotic.

Sources:

1. https://www.healthline.com/nutrition/probiotics-101#section1
2. https://www.livestrong.com/article/411260-how-to-test-probiotic-supplements/
3. https://www.wikihow.com/Make-Yogurt
4. https://www.consumerlab.com/answers/is-the-probiotic-milk-test-effective-in-testing-the-quality-of-the-bacteria-in-probiotic-supplements-at-home/probiotic-milk-test/
5. https://www.researchgate.net/profile/Effie_Tsakalidou/publication/257067497