Yogurt: how cultures change the structure of milk

Useful to know

Yogurt is an example of how microorganisms are involved in creating a known nutritional structure. In the Codex standard for fermented milks, products are described by fermentation with suitable microorganisms and lowering the pH, with or without coagulation. [1] This is different from arbitrary pickling of left milk. To understand the product, the defined culture and the managed conditions are important. The sour taste itself does not explain the entire technological pathway by which the food was obtained.

For yoghurt, Codex indicates joint cultures of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. The standard also distinguishes other fermented milks according to the cultures used. [1] This gives a glossary for a more accurate comparison of products. The general feeling of sour milk product does not automatically mean the same set of microorganisms. When discussing a label, one should look at the exact name and description of the composition, instead of different fermentation traditions being collected into one undefined category.

Tetra Pak's technology manual explains how culture converts some of the lactose into lactic acid. The decrease in pH is involved in the collection of casein particles and the formation of a protein network with proper pre-treatment. [2] For the consumer, this is perceived as the soft gel-like structure. Thus, density is not an isolated property that is simply added to the liquid. It is associated with changes in the composition and organization of milk proteins during the process.

The handbook looks at various technological forms, including a product that is shaped in the package, and a product that is stirred after fermentation. [2] This is a useful distinction when observing consistency. Two packs can have a different feel without just this difference proving quality or lack of quality. It is necessary to know what type of product is being compared. The preparation, stirring and composition are separate parts of the explanation of the final appearance.

Codex also makes a distinction for post-fermentation products where the requirement for viable microorganisms is considered differently. [1] The word "fermented" should therefore not be used alone as evidence of the same condition of cultures in any food. For a consumer comparison, it is more useful to read the manufacturer's designation and directions. From one feature such as density, sour taste or color, the entire processing history cannot be restored.

As a practical example, two unflavored products can be compared by recording the name, composition and feel at the same serving temperature. It's a culinary observation, not a laboratory assessment of cultures. The useful result is a more accurate vocabulary of preferences and usage: smoothness, density and way of mixing with other ingredients. Understanding fermentation provides a basis for this choice when technological facts are kept separate from personal taste and from unsupported promises of health effects.