Aged cheeses on a board with grapes

Fermented Cheese: What You Need to Know

ByCraig Brockie Last updated

What fermented cheese means

Fermented cheese is cheese made by letting bacteria sour the milk, and that describes most cheese. Starter cultures turn milk sugar (lactose) into lactic acid, which the Dairy Science and Technology eBook calls their primary job. What differs from one cheese to the next is how many of those microbes are still alive when you eat it.

There are exceptions. The ISAPP consensus statement on fermented foods, which defines them as foods made through desired microbial growth and enzymatic conversions, notes that some soft cheeses can be made by chemical acidification instead of fermentation. Whether cheese counts as a probiotic is a separate question, covered in Is Cheese a Probiotic?; this article explains the fermentation itself and what happens to the microbes afterward.

How cheese fermentation works

Cheddar is a good example because its steps are written into federal rules and well studied. The U.S. standard for cheddar cheese requires the milk to be subjected to a lactic acid-producing bacterial culture. A 2022 study of long-ripened Cheddar describes the rest of the process:

  1. Culture and set: starter bacteria, mainly strains of Lactococcus lactis, ferment lactose into lactic acid, and rennet sets the milk into curd.
  2. Drain and cheddar: the curd is cut and stacked so whey drains out while acid keeps developing.
  3. Mill and salt: the curd is milled and dry-salted, which halts the starter’s acid production.
  4. Press and ripen: blocks are pressed and ripened at about 39°F to 46°F (4°C to 8°C) for 4 months to more than 2 years.

During ripening, enzymes from both starter and non-starter bacteria break down protein and fat, which builds the texture and flavor of aged cheese. Cheddar turns from smooth to slightly crumbly and sharp as it ages, so the microbes keep working long after the cheese is made.

What happens to the microbes as cheese ages

Wheels of cheese aging on wooden shelves

In the Cheddar study, researchers at the University of Guelph followed industrially made Canadian Cheddar from fresh curd to 30 to 32 months. They note that starter bacteria lose viability over time as lactose runs out (around 30 days into Cheddar ripening), along with low moisture, acidity and salt. Other lactic acid bacteria, called non-starter bacteria and mostly lactobacilli, gradually take over.

Even so, the cheese did not end up free of bacteria. Plate counts of starter-type bacteria fell from roughly 10 million to 1 billion per gram in fresh curd to about 1 million to 5 million per gram at 30 to 32 months. This was one study of one cheese style, but it shows that long aging does not necessarily leave a cheese without live bacteria.

Which cheeses tend to keep live cultures

A 2022 study in the Journal of Nutrition had experts estimate live microbes in foods eaten in the U.S. The ratings were estimates from expert review and published research, not lab counts of individual products. In the full paper, the authors placed most cheeses in their highest group, above 10 million live microbes per gram, with three exceptions:

Type of cheeseExamplesExpected live microbesWhy
Natural, aged, eaten unheatedCheddar, gouda, SwissHighFermented and not heat-treated afterward
Long-agedParmesanRated lowerLong aging
Pizza-type cheeseMozzarella on pizzaRated lowerUsually heated before eating
Pasteurized process cheeseAmerican slicesRated lowerA pasteurized product, heated to at least 150°F for 30 seconds during manufacture (21 CFR 133.169)

Cooking cheese at home follows the same logic: the experts rated pizza-type cheese lower because it is usually heated before eating, even though it was made by fermentation. ISAPP suggests that foods pasteurized after fermentation be described as “made by fermentation” rather than as containing live cultures. Fresh cheeses vary by maker; our guide to whether cottage cheese has probiotics explains how to read those labels.

Fermented cheese and gut health

Fermented foods as a group have some human research behind them. In a 17-week Stanford trial with 18 healthy adults per group, a diet high in fermented foods steadily increased microbiome diversity and lowered inflammatory markers. The fermented foods participants ate included yogurt, kefir, kimchi and fermented cottage cheese; the study did not test aged cheese on its own.

So aged cheese is best seen as one fermented food among several rather than a gut treatment. Our guide to fermented foods for gut health compares the options, and probiotic foods covers foods with named, studied strains.

Lactose, sodium and saturated fat

Fermentation and ripening leave most hard cheeses with very little lactose. NIDDK notes that hard cheeses like cheddar or Swiss are lower in lactose than other milk products, and some people with lactose intolerance tolerate them more easily. The tradeoff is sodium and saturated fat, so portion size matters. Values below are calculated from USDA FoodData Central; percentages use the FDA Daily Values of 2,300 mg sodium and 20 g saturated fat.

Food (USDA FoodData Central)ServingLactoseSodiumSaturated fat
Cheddar1 oz0.03 g185 mg (8% DV)5.4 g (27% DV)
Swiss1 oz0 g53 mg (2% DV)5.2 g (26% DV)
Parmesan, hard1 oznot listed335 mg (15% DV)4.2 g (21% DV)
Feta1 oznot listed323 mg (14% DV)3.8 g (19% DV)
Blue cheese1 oznot listed326 mg (14% DV)5.3 g (27% DV)
American, pasteurized process1 oz0.6 g473 mg (21% DV)5.1 g (26% DV)
Cottage cheese, creamed4 oz3.0 g356 mg (15% DV)1.9 g (10% DV)
Whole milk, for comparison1 cup12.3 g105 mg (5% DV)4.5 g (23% DV)

Swiss stands out for low sodium, while feta, blue and processed cheese carry several times as much per ounce.

Raw-milk cheese, listeria and pregnancy

Some fermented cheeses are made from raw (unpasteurized) milk. U.S. rules allow raw-milk cheddar if it is aged for at least 60 days at no less than 35°F (21 CFR 133.113). CDC advice for higher-risk groups to avoid raw-milk cheese still applies to aged raw-milk cheeses.

The CDC says pregnant women are 10 times more likely to get a Listeria infection. For pregnant people, adults 65 and older and people with weakened immune systems, it advises avoiding any cheese made with raw milk and unheated queso fresco-type cheeses, even when pasteurized. It lists hard cheeses made with pasteurized milk, such as cheddar, Parmesan and Swiss, as safer choices, and says soft or raw-milk cheeses can be eaten if heated to 165°F or until steaming hot.

According to the CDC, Listeria in pregnancy usually causes fever and flu-like symptoms, and can lead to miscarriage, stillbirth or a life-threatening infection in the newborn. Contact a healthcare provider if you ate a recalled or outbreak-linked cheese and develop a fever or other symptoms. This article is general information, not medical advice.

How to choose fermented cheese

  • For live cultures: pick natural aged cheese such as cheddar, gouda or Swiss over processed slices, and eat some of it unheated.
  • For low lactose: hard, aged cheeses are the usual first choice.
  • For sodium: Swiss is among the lowest; feta, blue and processed cheese are among the highest.
  • For pregnancy or a weakened immune system: look for “made with pasteurized milk” on the label.
  • For portion control: keep servings near 1 ounce because of the saturated fat.

Related topics

Sources

Craig Brockie is the founder of Ultimate Health Solutions, the company behind Ultimate Gut, and the author of Ultimate Health, The Ultimate Gut Health Guide and The Unlimited Probiotics Guide. After injuries and chronic health problems in his twenties that conventional care didn’t resolve, he began researching health on his own and has studied natural health for 30 years. He is not a medical professional, and his articles are general information, not medical advice.

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