Doctor Says Liquid Atop Yogurt Is Protein, Not Spoilage

Pouring off the clear liquid that collects on the surface of yogurt costs consumers nutrients, experts say. The liquid is not a sign of spoilage but whey, one of the two main proteins in milk. Specialists advise stirring it back in.

Amir Khan, a general practitioner with Britain's National Health Service (NHS), recently urged people not to discard the liquid. "The whey on top of the yogurt many of us eat for breakfast is rich in protein and various nutrients," Khan said. "It looks like it has gone off, but it is actually whey that has separated naturally from the yogurt." He added, "Whey is like liquid gold. Don't pour it down the sink — just stir it back into the yogurt."

The liquid's identity is explained by how yogurt is made. Milk protein is divided into casein and whey protein. During fermentation, casein coagulates into a thick mass, while whey protein remains liquid and rises to the surface. Along with protein, whey contains calcium, potassium and B vitamins. Whey protein helps maintain muscle mass and bone health, and combined with a balanced diet and exercise it can also aid weight management.

Growing interest in yogurt is visible in market data as well. According to market research cited by the Food and Beverage News, domestic fermented milk sales rose for a third straight year, from 994.1 billion won in 2023 and 997.4 billion won in 2024 to 1.01 trillion won ($700 million) in 2025. Spoonable yogurt accounted for 46.7% of that total, the largest segment. Sales of drinkable and liquid types fell 3.5% and 7.6%, respectively, from a year earlier. Greek yogurt, marketed on high protein and low sugar, more than doubled in two years, from 54.5 billion won in 2023 to 111.6 billion won in 2025. Retail sales of fermented milk in the first half of 2025 reached 558.6 billion won, up 1.6% from a year earlier, according to food industry statistics from the Korea Agro-Fisheries & Food Trade Corporation (aT).

Yogurt also serves as an alternative for consumers who struggle with dairy. Lactose intolerance is a metabolic condition caused by a deficiency of lactase, the enzyme that breaks down lactose. Undigested lactose draws water into the small intestine, causing bloating, cramps and diarrhea. Because enzymes produced during fermentation break down some of the lactose, yogurt tends to trigger these symptoms less. Conditions in South Korea, however, differ from conventional wisdom. In a survey of prevalence and distribution of lactose intolerance among Koreans, conducted by a joint research team from Dankook University and Eulji University on 623 people aged 14 to 59, prevalence based on gastrointestinal clinical symptoms was 31.9%. That is far below the widely held belief that three of every four Koreans are affected. About 74% of those who experienced symptoms did so within two hours of consuming dairy. In most cases, however, severity ranged from mild to moderate and did not interfere with daily life.