It's very common for yogurt to get watery after opening, and it's usually nothing to worry about!1 The liquid you see is called whey, and its separation from the thicker yogurt is a natural process known as syneresis.2
Here's why it happens:
- Yogurt is a Gel: Yogurt is essentially a gel formed by milk proteins (casein) that have coagulated due to lactic acid produced by beneficial bacteria during fermentation.3 This protein network traps water and other components, giving yogurt its thick texture.
- Protein Contraction: Over time, especially after the yogurt has been disturbed (like opening it, spooning some out, or moving the container), this protein network can contract. As it contracts, it squeezes out some of the trapped liquid, which is the whey.4
- Post-Fermentation Acidification: The active bacteria in yogurt continue to produce lactic acid, even when refrigerated.5 This continuous acidification can cause the gel to further contract and release more whey.6
- Physical Disruption: Simply opening the container, dipping a spoon in, or even the jostling from transportation can disrupt the delicate protein matrix, leading to the release of whey.
- Temperature Fluctuations: While the fridge helps, slight temperature changes can also contribute to whey separation.7
- Lack of Stabilizers: Yogurts labeled "all-natural" or those without added stabilizers (like pectin, starch, or gelatin) tend to show more syneresis because they rely solely on the natural protein network to hold the liquid. Greek yogurt, which is strained to remove most of the whey, generally has less liquid because it has a higher protein content.8
Is it safe to eat?
Yes, in most cases, watery yogurt is perfectly safe to eat. The whey is nutritious, containing some protein, vitamins, and minerals.9 You can simply:
- Stir it back in: This is the most common approach and will help reincorporate the nutrients and thin out the yogurt slightly.10
- Pour it off: If you prefer a thicker consistency, you can pour off the excess whey.11 Don't throw it out, though! It can be used in smoothies, soups, or even as a base for dressings.12
When to be concerned:
While some whey is normal, excessive liquid accompanied by other signs of spoilage means it's time to discard the yogurt:
- Mold or discoloration: Any fuzzy spots (green, pink, black, or grey) or unusual colours.
- Foul smell: A rancid, strongly sour (beyond normal yogurt tang), or unpleasant odor.13
- Lumpy or curdled texture: If the yogurt is no longer smooth and has noticeable lumps or a very gelatinous, unappetizing texture.
- Bloated container: If the container itself looks swollen, it could indicate gas production from spoilage bacteria.
In summary, a watery layer on top of your opened yogurt is almost always a normal sign of whey separation and is safe to consume.14
小雨也查一下。
