Probiotics are live yeasts and bacteria that can contribute to your existing gut microbiota to provide a wide range of potential health benefits. Your digestive system features a vast, diverse community of bacteria that can support your digestive health and contribute to the overall health of your entire body. Probiotics are found in a variety of fermented foods, like kimchi, yogurt, and kefir, as well as dietary supplements.1
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 their probiotics. This test is simply known as the “milk test.”
What is the 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.
- Pour 4 ounces of the cold milk into a glass. Add the probiotic capsules or powder into the milk.
- Place the glass of milk and probiotic uncovered in a room temperature area in your home.
- After up to 48 hours, check the glass to see if the milk has curdled.
The test is designed to measure the ability for the probiotic bacteria to create lactic acid which curdles the milk proteins. The thinking is that live probiotics that are able to ferment lactose, a sugar found in milk, to lactic acid2. Seeing curdled milk is a sign of some kind of bacterial activity.
The Milk Test and YogurtYogurt is one of the most well-known probiotic-rich foods that requires a much more intensive, controlled process than the one described by the milk test. Yogurt starts with heating milk to about 185 degrees Fahrenheit. The milk is then cooled.
Once the milk has cooled, the bacteria are added to start the fermentation process. This bacteria can come from freeze-dried bacteria or a starter culture from store-bought yogurt that contains live cultures. The actual amount and type of bacteria added can vary based on the recipe or the manufacturer, but by definition, yogurt production requires Lactobacillus bulgaricus and Streptococcus thermophilus. Some yogurt manufacturers may also add Lactobacillus acidophilus. These good bacteria are necessary for metabolizing the lactose in the milk and forming lactic acid, which begins the fermentation process and imparts the sour flavor that is characteristic of yogurt.4
From there, the mixture of milk and bacteria still requires incubation. At home, that could mean using an oven, rice cooker, or food dehydrator, but the key is keeping the mixture at a temperature of 100 degrees Fahrenheit. Heating the mixture too high above this point would kill the bacteria, while lower temperatures would prevent the bacteria from working optimally. The mixture also has to be sealed during the fermentation process to keep out air and light. Oxygen could act as a contaminant during the fermentation phase, while direct sunlight can kill off the probiotic bacteria.3
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. Clumping occurs when milk becomes acidic enough that proteins start joining together. Only certain probiotics can make milk acidic by converting lactose to lactic acid.
The organisms that create yogurt, Lactobacillus bulgaricus and Streptococcus thermophilus, are categorized as facultative anaerobes, meaning that they can live in environments with some but not a lot of oxygen. With too much oxygen, they can be damaged6. Most probiotic supplements are optimized for survival in the anaerobic environment of the gut.
To optimize yogurt production, manufacturers use large, industrial-grade containers that are sealed and heated to keep out oxygen and ensure probiotic activity. Most bacteria grow best around 100 degrees Fahrenheit. The temperatures are highly controlled to ensure consistency and optimal probiotic growth.
The environment in which yogurt is produced is unlike the environment of your kitchen counter. It has oxygen and the temperature is not controlled. With the milk test, you probably won’t see much clumping even with active probiotics.
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.
The milk test is also unreliable with probiotic pearls or tablets that have not been crushed. Tablets normally break down when subjected to heat and agitation within the stomach. Putting whole tablets into the milk would obviously show no effects as the probiotics can’t even make it out into the milk. The same goes for probiotic products with enteric coatings.5 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.
The at-home milk test of probiotics ultimately cannot be relied on to gauge the effectiveness of a probiotic supplement, leaving you with nothing more than some wasted probiotic products and a glass of room-temperature milk. The only real way to determine the viability and effectiveness of a probiotic is through lab testing under controlled, anaerobic conditions, allowing researchers to eliminate any contaminants and minimize the amount of oxygen in the testing environment. 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.
DrFormulas™ Nexabiotic® Advanced Probiotics and Prebiotics for Women and Men features 23 different probiotic strains with 17.25 billion CFUs per capsule and has been lab tested for quality and viability, ensuring that you get the most out of each serving without needing to rely on a milk test.