Yeast and mold in yogurt: Five facts everyone should know

Nothing is more off-putting than opening up a container of yogurt and much to your surprise, seeing that mold has taken over the surface. Or, even worse, taking a taste of yogurt that looks fine and immediately realizing it is past its prime.

This type of yeast and mold contamination is a leading cause of spoilage in yogurt and other cultured dairy products. Yogurt is simply milk acidified by specific strains of bacteria, and can be made easily in a microbiology class or even at home. Typically, the heat used during the processing stage and the low acidity of the product, are sufficient barriers to pathogen growth in yogurt.

However, if the milk contacts yeast and mold in the growth stage of the yogurt culture, conditions become perfect for the growth of yeast and mold in the product.

Most yeast and mold contamination comes from the air around the tanks that hold the milk. There are many thousands of wild yeast and mold strains in the air and soil, and if they reach the milk, they have found an optimal medium for growth. It is important to note that the majority of human exposures to mold toxins come from eating food contaminated with mold, not the environment.

More information about yeast and molds in yogurt:

1. Molds are fungal organisms that break down plant and food waste. Mold can range in color from white to orange, to green or black.

1. Mold can show up in a range of ways, including having a hairy or fuzzy appearance or appear porous, like a sponge. Molds tend to spread by extending fibers, reaching further and further across a food surface.

1. Yeast is also a fungal organism, but unlike the spreading mold, yeast is most often seen as a white dot or grouping of dots. Yeast is usually creamy to a crisp white color, which makes it difficult to spot in cultured dairy products. It can also be embedded in the product, not just on the surface.

1. Yeast can look glossy or gel-like, but it is usually hard to spot in yogurt and other cultured dairy products, due to the product’s creamy to white color. Yeast can also produce gas that causes packaging to puff or bloat or can cause a product to foam and have a bubbled texture.

1. Mold produces a sour or gritty taste in contaminated products, while yeast is known for tangy, or alcohol-like flavors.

In order to ensure the safety and quality of cultured yogurt products, food safety testing should be completed at various levels throughout the production process. Neogen can assist you with this through our sensitive line of yogurt solutions, which screen for contaminants such as yeast and mold.