Yogurt is made from just two things: milk and live bacterial cultures. That’s it for the basic product. Bacteria feed on the natural sugar in milk, producing acid that thickens the liquid into the creamy, tangy food you find in the dairy aisle. Everything else on the ingredient label, from sweeteners to thickeners, is an addition to that core process.
The Two Required Ingredients
Under FDA regulations, yogurt must start with a dairy base (cream, whole milk, reduced-fat milk, skim milk, or reconstituted versions of any of these) and be fermented with two specific bacteria: Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. Without both of those bacterial species, the product can’t legally be called yogurt in the United States.
The milk provides protein, fat, calcium, and lactose, which is milk’s natural sugar. The bacteria provide the transformation. If you’ve ever made yogurt at home, you know the recipe is almost absurdly simple: heat milk, cool it down, stir in a spoonful of existing yogurt as your starter culture, and keep it warm for several hours.
How Bacteria Turn Milk Into Yogurt
The two bacterial species work as a team. S. thermophilus gets to work first, breaking lactose into its two component sugars and preferentially consuming glucose while releasing galactose back into the milk. L. bulgaricus follows, and together they convert those sugars into lactic acid. This is the entire engine of yogurt making.
As lactic acid accumulates, the pH drops and the milk becomes increasingly acidic. That acidity causes milk proteins, primarily casein, to unfold and bond together into a gel-like network. This is what gives yogurt its thick, semisolid texture without any mechanical thickening. The acid also creates yogurt’s characteristic tang and acts as a natural preservative by making the environment hostile to harmful bacteria.
What Makes Greek Yogurt Different
Greek yogurt starts as regular yogurt. The difference is a straining step. After fermentation, the yogurt is passed through a fine mesh or cloth for eight to twelve hours, which drains off a yellowish liquid called whey. Whey carries water, some lactose, and minerals with it. What stays behind is denser, higher in protein per serving, and noticeably thicker.
This is why Greek yogurt typically has roughly twice the protein of unstrained yogurt. A 100-gram serving of plain whole-milk Greek yogurt contains about 9 grams of protein, along with 100 milligrams of calcium and a surprisingly high dose of vitamin B12, covering about 31% of the daily value.
Common Additives in Store-Bought Yogurt
Plain yogurt can be made with nothing but milk and cultures, but most commercial yogurts include additional ingredients for texture, sweetness, or shelf stability.
- Thickeners and stabilizers: Gelatin, pectin, carrageenan, gum arabic, modified starches, and sodium alginate are all used to prevent whey from separating and to give yogurt a smoother, more consistent mouthfeel. These are especially common in low-fat and fat-free varieties, where removing fat makes the texture thinner.
- Sweeteners: Flavored yogurts almost always contain added sugar. Fruit preparations blended into yogurt can be nearly 50% sucrose by weight, with the remainder being water, fruit, citric acid for tartness, and a preservative like potassium sorbate. Some brands use alternative sweeteners like allulose or stevia extracts to reduce sugar content.
- Fruit and flavorings: “Fruit on the bottom” products use cooked fruit preparations that are essentially jam. Vanilla yogurt typically gets its flavor from vanilla extract added to a sweetened base. Artificial or natural flavorings round out the list.
If you want yogurt with the fewest ingredients, look for plain varieties where the label reads something close to “milk, live active cultures” and nothing else.
Live Cultures and the NYA Seal
Not all yogurt on the shelf still contains living bacteria by the time you eat it. Heat-treated yogurt, sometimes labeled “heat-treated after culturing,” kills the bacteria to extend shelf life. If living cultures matter to you, look for the National Yogurt Association’s “Live & Active Cultures” seal. That voluntary certification means the product contained at least 100 million cultures per gram at the time of manufacture. Frozen yogurt has a lower threshold of 10 million per gram.
Yogurt From Other Milks
Cow’s milk is the most common base, but yogurt can be made from the milk of goats, sheep, water buffalo, and camels using the same bacterial cultures and fermentation process. The results differ because the milks differ. Sheep milk has the highest fat and protein content of the common options, producing a richer, thicker yogurt. Goat milk is higher in medium-chain fatty acids, which some people find easier to digest. Water buffalo milk, the base of many traditional South Asian yogurts, is notably higher in protein and minerals than cow’s milk.
Plant-Based Yogurt Alternatives
Plant-based yogurts replace dairy with a liquid base made from soy, coconut, almond, oat, or cashew. Soy and coconut dominate the market. These products are still fermented with bacterial cultures, but because plant milks lack casein, they don’t naturally thicken the same way. Manufacturers compensate with added starches like tapioca, protein isolates from peas or almonds, and gelling agents.
Pea protein isolate, which is about 86% protein, is a common addition to boost the nutritional profile closer to dairy yogurt. Almond protein forms gels more readily than soy protein, which is one reason almond-based yogurts can achieve a texture closer to the dairy original. The trade-off is a longer ingredient list. Where plain dairy yogurt needs two ingredients, a plant-based alternative might need eight or ten to approximate the same taste and consistency.