The liquid isn't harmful, but it's probably not something you want in your morning bowl of yogurt.
bowl of yogurt with fresh fruit
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If you've ever peeled back the lid of a yogurt container to find a layer of what looks like water but is actually whey protein on top, you may have wondered why it's there. "A little bit of whey will naturally separate from the milk curds in yogurt," says Elizabeth Conover, brand director of Stonyfield Organic Yogurt. Whey is one of the main proteins found in dairy products and it contains essential amino acids that help carry out the functions that proteins perform in the body. Although the nutrient-dense liquid isn't harmful, it's probably not something you want in your morning bowl of yogurt. Is there a way to limit the amount of whey that forms at the top of your container? And if not, how do you get rid of it? To answer these questions, we consulted two experts. 

Why Does Whey Form?

Regular yogurt is made by heating milk, letting it cool, then adding beneficial bacteria for fermentation. During the heating process the whey proteins are denatured, increasing their water binding capacity and allowing them to easily cluster with other milk proteins to make the yogurt firmer. The yogurt is then left to rest until it forms a thick, firm texture. As time goes on, however, "the whey that's trapped in the product is kind of squeezed out," explains Robert Roberts, Ph.D., head of the department of food science at Pennsylvania State University. He further notes that the whey needs somewhere to go so it travels around the outside or to the top of the yogurt container, forming a layer of liquid. 

There are a few different factors that contribute to how much whey separation occurs in yogurt. One of the most important things to consider is how much protein is in the product. Increasing the amount of protein increases gel firmness and decreases whey separation, which is commonly referred to as syneresis. Greek yogurt, which has been strained to remove most of the whey, has a higher protein content, which is why you'll find less liquid in a container of Greek yogurt than regular yogurt that hasn't been strained. 

Additionally, the type of stabilizer used during production also plays a role in the amount of whey separation that occurs in yogurt. Different stabilizers used in yogurt include alginates, gelatins, gums, pectin, and starch. "If you have starch as a stabilizer, for example, it's less likely to synerese than if you don't see any," Dr. Roberts says. If you don't see a stabilizer listed on your yogurt container, as is the case with all-natural products, there will be more syneresis than if you used starch, pectin, or another stabilizer, according to Dr. Roberts. At Stonyfield Organic, Conover says they don't use gelatin in their yogurt and instead opt for a small amount of pectin sourced from citrus peel to help stabilize the yogurt, meaning that whey separation is common in some of their products. 

Beyond the protein content and type of stabilizer used, whey separation is also accelerated by a process called post fermentation acidification. "During storage it's not uncommon for yogurt to get more acid as the enzymes that are produced by the bacteria continue to lower the pH," Roberts explains. "As the pH lowers, the gel contracts and as the gel contracts more whey is expressed." What's more, additional acid is produced once the product has been disrupted, which is why more of the liquid substance commonly appears once you've opened the product, as it has been jostled around from the store to your home to the refrigerator and so on. 

What to Do with the Whey

Even though the whey isn't harmful, perhaps like us you prefer a scoop of yogurt that's firm and has an even consistency? While there isn't really a way to entirely avoid the liquid from forming, you can return your yogurt to its original state by simply stirring the whey back in or pouring it off the top. If you choose to remove it, don't throw it out; Conover recommends using it in smoothies, dressings, and soups. "The whey does contain some vitamins and nutrients, so it's worth utilizing," she says.


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