Improving Milk for Fermentation
In the production of cultured milks, the best possible growth conditions must be created for the starter culture. These are achieved by heat treatment of the milk to destroy any competing microorganism. In addition, the milk must be held at the optimum temperature for the relevant starter culture. In addition to flavor and aroma, correct appearance and consistency are very important features for the consumer. These are mainly determined by adequate preprocessing parameters: heat treatment and homogenization of the milk, sometimes combined with methods to increase the MSNF content (as for milk intended for spoonable yogurt), are essential “foundation stones” for the construction of the coagulum during the incubation period.
Modifying Milk Composition
Pretreatment of the milk is almost the same for all cultured milks. Milk fat standardization is a consolidated practice in fermented milk production: full fat, partially, and totally skimmed products are distributed in most countries even if an agreement on common limits of fat content per each category has not been reached. Milk fat content generally varies from 0% to 10%. Codex Standard 243-2003 sets maximum limits (15% for yogurt) but does not define product categories based on their fat content. In Italy, for yogurt whole fat means > 3% and skimmed < 1%, whereas partially skimmed is intended to be yogurt prepared from milk with 1.5% to 1.8% m/m fat.
Another key point is that to reach the desired consistency (i.e., the first quality characteristics expected by consumers), it is essential to increase the milk dry matter and notably the protein content. In Italy, a domestic law (L.138/1974) forbids dairies to hold and make use of totally or partially dehydrated/reconstituted or purchased concentrated milk.
Dairies are allowed to culture concentrate milk by evaporation or membrane techniques only in the factories that prepare and pack fermented milks. In all the other European countries, it is allowed not only to concentrate but also to enrich milk with any other milk-based product, such as skim/whole milk powder, dry buttermilk, whey, milk proteins, casein, and caseinates. Codex Standard 243-2003, coherently with its role of supernational minimal standard, lists as raw materials milk and milk products, reconstitution water where necessary, and a number of ingredients (dairy and nondairy) and additives to be used according to the type of fermented milk—always in compliance with local regulations.
In the case of sweetened fermented milks, the addition of sugar, syrups, or concentrated sweeteners is generally made after fermentation, in line before packaging, through sweetened fruit/nonfruit preparations. It is, however, feasible, provided the starter culture is able to ferment the mix in a technologically reasonable time, to add sweeteners and other characterizing ingredients to the milk before heat treatment and homogenization. These include coffee or malt extracts, fibers, or thickeners, for example.