Buttermilk

True buttermilk is composed of the low-fat portion of milk that remains after the cream has been churned into butter. Traditionally, its thickness and flavor develop by mild fermentation.  It has remnants of fat globules that make it an excellent emulsifier like lecithin; a characteristic that make it valuable in the preparation of finely-textured foods. True buttermilk is slightly acidic and has a subtle, complex flavor. Regrettably, it is prone to spoilage and off-flavors.

A shortage of true buttermilk after World War II led to the development of imitation “cultured buttermilk.” It is made from ordinary skim milk that is fermented.  The process follows that of yogurt, but the fermentation is stopped abruptly by rapid cooling. The gelled milk is then agitated to produce a thick, smooth liquid. Most buttermilk sold in the US is not true buttermilk but rather imitation cultured buttermilk.   

Bulgarian buttermilk has yogurt cultures that have replaced the cream cultures. It has increased acidity by fermentation also at higher temperatures; thus it resembles yogurt.

Sour cream

Sour cream is a leaner, firmer version of crème fraîche. It contains 20% milk fat and enough protein to curdle when cooked. It appears to have originated from Central and Eastern Europe and brought to the US in the 19^th century.  Since then, Americans have added a small amount of rennet, which contains enzymes that cause protein coagulation. The result is a heavier, firmer sour cream than its European counterpart.

Acidified sour cream is made by coagulating milk with acid instead of through fermentation. It is therefore also known as non-fermented sour cream. Manufacturer versions of low fat and non-fat sour cream replace butterfat with starch, plant gum, and dried milk protein.

Crème fraîche

Crème fraîche is 30% milk fat pasteurized at moderate temperatures. It is not made from UHT (Ultra High Temperature) pasteurized or sterilized milk. Two versions are available: liquid and thick. The liquid crème fraîche is unfermented. It has a shelf life of 15 days. The thick version is fermented with a typical cream culture. It has a shelf life of 30 days.

A home-made version of crème fraîche is made by adding cultured buttermilk or sour cream to heavy cream (1 tbsp per cup) and letting it stand at cool room temperature for 12 to 18 hrs or until thick.

Cream cultures

Cream cultures such as sour cream, crème fraiche, and buttermilk are indigenous to Western and Northern Europe. These products result from the slow fermentation produced by the mesophilic bacteria Lactococci and leuconostoc species. These bacteria have three important characteristics that make them ideal for production of creams and buttermilk: 1. They grow best at moderate temperatures. The process of fermentation can be kept at lower temperatures than those that produce yogurt. 2. They are moderate acid producers. Again, it prevents the formation of yogurt from too acidic a condition. 3. They complement flavor by turning citrate into diacetyl; a compound which gives the fermented milk product a characteristic buttery flavor.