Food-grade lactic acid: fermentation and E270

Despite its name, food-grade lactic acid does not come from milk. It is an acidifier produced industrially by fermenting plant sugars—beet, corn, cane—and a natural fermentation product in yogurt, sauerkraut, sourdough bread, or dry-cured meats. It is labeled E270. Its role involves four functions: lowering pH, preserving, texturing, and flavoring. This page explains where it comes from, how to identify it, and why it has nothing to do with the lactic acid used in cosmetic care.

One molecule, two possible origins

Lactic acid corresponds to the formula C₃H₆O₃. It is a simple organic acid, resulting from the degradation of glucose by bacteria in the absence of oxygen.

In fermented foods, it forms on-site: lactic bacteria present in milk, on vegetables, or in a sourdough starter transform available sugars and release the acid, which lowers the pH of the medium.

As an industrial additive, it is produced separately, by fermenting plant sugars in tanks, then purified and added to the finished product. This is the form labeled E270.

Its name comes from its historical identification in sour milk in the 18th century—an etymological origin, not a manufacturing origin. This distinction has a direct practical consequence: the mention E270 on a label never indicates the presence of milk, and a product containing lactic acid can perfectly be vegan.

Its pKa is around 3.86, making it a weak acid: at a pH close to this value, it exists half in acid form and half in lactate form. This buffering property makes it useful for stabilizing the acidity of a preparation.

L and D forms, and why they are mentioned

The molecule exists in two non-superimposable mirror forms: L(+)-lactic acid and D(−)-lactic acid.

The human body naturally produces and metabolizes the L form, which appears in muscles during exertion. It breaks it down without difficulty.

The D form is metabolized more slowly. Bacterial species used in fermentation produce varying proportions of these forms: some yield almost exclusively L, others a racemic mixture.

This distinction explains a recommendation sometimes encountered regarding infant formulas, whose metabolism is immature. For a healthy adult and in the quantities present in food, the question does not arise in practice.

How yogurt becomes yogurt

This is the most striking example of the acid's texturizing role.

Two bacteria—Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus—are inoculated into milk heated to around 43 °C. They consume some of the lactose and release lactic acid.

The pH gradually drops from 6.7 to 4.6, a value that corresponds to the isoelectric point of casein. At this pH, casein micelles lose their charge, stop repelling each other, and aggregate into a gel: the milk changes from liquid to firm without any thickener being added.

Fermentation then continues slowly to about 4.0, which accentuates the perceived acidity. This is why yogurt aged in the refrigerator becomes more acidic than when it leaves the factory.

A point often overlooked: yogurt heated after fermentation—labeled "heat-treated"—still contains its lactic acid, but no live cultures. Acidity and probiotics are two distinct things.

Lacto-fermented vegetables: salt is key

Sauerkraut and kimchi rely on a different mechanism: nothing is inoculated, but rather selected.

Salt creates an environment where the lactic flora naturally present on vegetables thrives while spoilage bacteria are inhibited. A 2% brine corresponds to 20 grams of salt per liter of water; for grated vegetables salted dry, it is 2% of the weight of the vegetables.

Fermentation occurs in three successive waves: Leuconostoc starts and produces gas, then lactobacilli take over and acidify more strongly, down to a pH of about 3.5.

Two conditions determine the result. The vegetables must remain entirely submerged—anything exposed will mold. And the temperature must remain moderate, between 18 and 22 °C: if warmer, fermentation accelerates and the result is soft.

The sign of success is measurable: a pH below 4.0, a distinctly acidic rather than putrid smell, and cloudy brine but without a fuzzy film on the surface.

Where to find it, in what form

Reading the table reveals a common logic: in almost all cases, acidification is what makes the food preservable. Below pH 4.5, most pathogenic bacteria, including Clostridium botulinum, no longer develop. This is a food safety mechanism before it is a matter of taste.

For dry sausage, rapid acidification by added cultures is even a critical step in the process: it makes the raw meat safe before drying takes over.

Reading E270 on a label

Lactic acid is among the oldest and most consensual additives. It is not subject to a quantified acceptable daily intake, its evaluation having concluded to a quantum satis use—the quantity necessary for the desired technological effect.

You will encounter it under several forms of mention: lactic acid, E270, or its salts—sodium lactate (E325), potassium lactate (E326), calcium lactate (E327). The latter are often used as preservatives or acidity regulators in prepared dishes and cured meats.

It is also found in products where it might not be expected: soft drinks, sour candies, sauces, industrial breads, prepared meals, and even some flavored waters.

What the label doesn't say: the exact quantity. Regulations require mentioning the additive, not its dose. Nor does it indicate the origin of manufacture—vegetable in almost all industrial cases, but without mandatory mention.

Its four roles in the food industry

Lactic acid is used in industry for specific technical reasons, and the same molecule fulfills different functions depending on the product.

As an acidity regulator, it adjusts and stabilizes the pH of a preparation. Its nature as a weak acid makes it an effective buffer: it maintains constant acidity despite process variations, which a strong acid cannot do as finely.

As a bacteriostatic agent, it inhibits microbial growth without destroying the product. In its undissociated form, it crosses bacterial membranes and disrupts their internal metabolism. This mechanism explains its use as a preservative in cured meats and prepared dishes.

As a flavor enhancer, it provides a distinct acidity but less aggressive than that of citric acid, with a longer persistence in the mouth. Manufacturers choose it when they seek a rounded acidic taste rather than a sharp one.

Finally, as a texturing agent, through its action on proteins—the mechanism described above for yogurt also applies to some fresh cheeses and dairy desserts.

A word about the industrial production process: the bacterial fermentation of plant sugars takes place in tanks at controlled temperatures, followed by purification by filtration and distillation. The resulting acid is very water-soluble and miscible in all proportions, simplifying its incorporation into liquid preparations.

Food-grade lactic acid and cosmetic lactic acid

It is the same molecule, and these are two unrelated uses. The confusion deserves to be clearly resolved, because it leads to risky actions.

In cosmetics, lactic acid is an exfoliating alpha-hydroxy acid, used at concentrations of 5 to 10% in over-the-counter products, at a precisely controlled pH between 3.5 and 4. It is this concentration-pH pair that determines its action on the stratum corneum. See our lactic acid page.

In yogurt, neither is controlled. The concentration is low, variable from one pot to another, and the pH has not been adjusted for cutaneous use. Yogurt applied to the face is not a peel: it is an unstandardized mixture whose parameters for exfoliant action are unknown.

Homemade recipes based on fermented foods are therefore improvisations, not dilutions of a known product. Our exfoliation and skin pH pages detail what pH control truly changes.

What "food grade" does not guarantee

It does not mean dairy product: the vast majority of industrial lactic acid is of plant origin.

It does not mean live cultures: an acidified, pasteurized food or one with added E270 contains the acid without containing active bacteria. Any probiotic effect depends on the bacteria, not the acid.

Nor does it mean that a homemade fermented food is automatically safe. A failed fermentation—insufficient pH, emerged vegetables, poorly cleaned container—produces food to be discarded, and appearance is not always enough to tell.

Finally, this page describes an ingredient and its technological role. It does not constitute nutritional advice, and a food intolerance or allergy should be discussed with a healthcare professional.

Same molecule, non-transferable use

A food additive is not dosed, buffered, or preserved for skin use: food grade says nothing about the pH or skin tolerance on the face. Exfoliation requires a formula designed for it—a lactic acid peel, with fixed concentration and pH—never a kitchen bottle.