Sour cream is made from cream that has been fermented with lactic acid bacteria. The bacteria convert lactose (the natural sugar in milk) into lactic acid, which thickens the cream and gives it that characteristic tangy flavor. In the U.S., sour cream must contain at least 18% milkfat by federal regulation.
The Core Ingredients
Traditional sour cream requires just two things: cream and bacterial cultures. Heavy cream provides the fat and body, while the bacteria do the work of transforming it into something thicker and tangier. In commercial production, pasteurized cream is inoculated with specific strains of bacteria, predominantly Lactococcus lactis, and held at a warm temperature (around 70°F to 90°F) for a controlled fermentation period.
If you’ve ever made sour cream at home, the process is even simpler. A common method combines about 1¼ cups of heavy cream with ¼ cup of whole milk and a couple tablespoons of lemon juice or white vinegar. The acid kickstarts fermentation, and after sitting undisturbed for roughly 24 hours at room temperature (67 to 72°F), the mixture thickens into sour cream. You can also buy culture starter packets that let you skip the milk and acid entirely, fermenting heavy cream on its own.
What’s in Store-Bought Sour Cream
Mass-produced sour cream often contains more than just cream and cultures. Manufacturers add stabilizers and thickeners to improve texture, extend shelf life, and prevent separation. The most common additives include guar gum, carrageenan (a seaweed-derived gelling agent), and mono- and diglycerides, which act as emulsifiers to keep the product smooth and uniform. Modified food starch is another frequent addition. If you want sour cream without these extras, check the ingredient label for brands that list only cream and live cultures.
Reduced-fat and fat-free versions rely more heavily on these thickeners to compensate for the body that fat would normally provide. A tablespoon of regular sour cream has about 47 calories, nearly 4 grams of fat (2.4 grams saturated), and 1.4 grams of protein. Light and nonfat versions cut the fat but tend to have longer ingredient lists.
Why It Tastes Sour
The tang comes directly from lactic acid. As bacteria feed on the lactose in cream, they produce lactic acid as a byproduct. This does two things at once: it lowers the pH of the cream, creating that sour taste, and it causes the milk proteins to coagulate, which is what makes the texture thick and spoonable rather than pourable. Historically, sour cream was simply cream that had been left to sour naturally from bacteria already present in unpasteurized milk. Modern production uses carefully selected strains to ensure a consistent flavor and safe product.
This fermentation also reduces the lactose content significantly. A 25-gram serving of sour cream contains less than 1 gram of lactose, which is why many people with mild lactose sensitivity can eat sour cream without issues. The bacteria have already broken down most of the sugar that would otherwise cause digestive trouble.
How It Differs From Crème Fraîche
Sour cream and crème fraîche are made through essentially the same process, but they differ in fat content and flavor. Crème fraîche has around 30% fat compared to sour cream’s minimum of 18%, giving it a richer, more velvety texture. Sour cream is tangier and thinner, while crème fraîche has a milder, nuttier flavor. The practical difference in the kitchen: sour cream curdles when heated because its higher protein and lower fat content makes it less stable. Crème fraîche can be stirred into hot sauces and soups without breaking.
Mexican crema falls somewhere between the two, with a pourable consistency and a gentler acidity than American sour cream. All three products start the same way, with cream and bacterial cultures, but the fat percentage and specific bacterial strains shift the final texture and taste.
Plant-Based Alternatives
Vegan sour cream skips dairy entirely and relies on high-fat plant ingredients to replicate the creamy texture. The most common base is raw cashews, soaked until soft and then blended smooth with water, lemon juice, apple cider vinegar, and salt. Some recipes add a small amount of Dijon mustard for depth. Store-bought versions may use coconut cream, tofu, or sunflower seeds as the base, with added starches and cultures to mimic the thickness and tang of traditional sour cream. These alternatives won’t have the same protein or fat profile as dairy sour cream, but they come close in texture and acidity when well made.