Dairy Ingredients span a whole range of applications in the dairy industry. You have ingredients for cheese, for butter, for whey, for milk powder, for lactose, etc. These are the ingredients that turn milk into so many exciting products with even more possibilities ahead. Today, so many manufacturers offer so many dairy ingredients and they are valued for their functions as well as their nutritional benefits. The food and beverage industries can offer the world so many tasty options thanks to food ingredients. Even more, they provide nutrition and so much versatility.
The Starter Cultures that are normally used in the production of cheese and other fermented dairy products are lactic acid bacteria which have the ability to produce lactic acid when added to milk. The production of lactic acid results in a lowering of the pH in the milk. The selection of the right culture for use in any dairy application will depend on the rate at which the pH is lowered and the minimum pH attained.
Types of Starter Cultures
a) Thermophilic cultures: These include Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. These cultures are generally used in combination to make yoghurt and certain cheese types such as Mozzarella Cheese (which can also be made with S. thermophilus alone) and Emmenthal Cheese.. Other less commonly used Thermophilic cultures include Lactobacillus helveticus and Lactobacillus delbrueckii subsp. lactis.
b) Mesophilic cultures: These include the non-gas forming cultures Lactocococcus lactis subsp. lactis and Lactocococcus lactis subsp. cremoris which are commonly used in the production of Cheddar Cheese (either with or without Thermophilic cultures) and Feta Cheese as also the fresh cheese types like Cottage Cheese and Quarg. The gas producing cultures include Lactocococcus lactis subsp. diacetylactic and Leuconostoc mesenteroides subsp. cremoris. These are commonly used in the production of Continental cheeses like Edam, Gouda Cheese and Emmenthal Cheese, Lactic Butter, Fermented Buttermilk, etc.
In the production process, cultures are influenced by incubation temperature, pH and time. Thermophilic cultures usually grow best at between 42-43°C while Mesophilic cultures normally perform best at around 30°C.
In Cheese production, the rate at which the culture is able to reduce the pH in milk is important as it, together with the action of the rennet should secure proper whey separation from the curd. Gas and aroma production by the cultures influence the direct (diacetyl) and indirect (cheese) flavours produced in the cheese. The gas produced is also important for eye formation in Continental Cheese.
In the production of Yoghurt and other fermented milk products, Thermophilic cultures influence the (acetaldehyde) flavour, viscosity and shelf-life of the curd.
Cultures are sold as a) Mother Cultures; b) Bulk Starter Cultures; or c) Cultures meant for Direct Inoculation. Mother Cultures and Bulk Starter Cultures constitute the traditional cultures that have to be propagated in media prior to inoculation in milk. Direct Inoculation Cultures are very highly concentrated cultures that can be inoculated directly into the milk in the processing vat. These cultures are supplied either as frozen cultures or as lyophilized (freeze-dried) cultures.
The choice of which culture is to be used will depend on the product to be produced, the process employed, cost-in-use of the culture and the desired quality of the end product. The type of cultures that can be used may be stipulated by legislation. The ability of the culture to resist bacteriophage, viruses that attack specific cultures and inhibit their growth, also influences the choice of culture.
Rennet is a proteolytic enzyme that is used mainly to make cheese. On its addition to milk, it coagulates or converts the casein micelles into a curd with whey separating from the mass.
There are mainly three different types of commercial preparations of rennet:
a) Animal Rennet – This is rennet in its natural form which is extracted from the stomachs of young calves. The active ingredient in this rennet is called chymosin. Until the early 1990s, most of the cheese produced worldwide was made with animal rennet. Animal rennet is normally supplied in liquid form. It is also offered as tablets to small cheese producers. Apart from chymosin, animal rennet also contains small quantities of pepsin and traces of lipase and other impurities. However strong resistance to its use from vegetarians and other animal welfare groups caused the development of factory produced alternatives such as microbial rennet and fermentation produced chymosin.
b) Microbial Rennet – It is sourced from fungi, bacteria and other microorganisms that produce chymosin. The most widely produced microbial rennet is made from the mold Mucor Meihei. It is sold in liquid, powder or granular form. The major disadvantage of microbial rennet is that the cheese tends to develop bitterness, especially those that need long ripening periods. Cheese yields with microbial rennet also tend to be marginally lower than those produced with chymosin.
c) Fermentation produced chymosin – these are produced from genetically modified organisms that yield chymosin that is 100% pure and identical to the chymosin found in animal rennet. This rennet is cheaper and, unlike calf rennet, is plentiful. The most widely used such chymosin today is produced from the fungus Aspergillus niger.
A few commercially available microbial rennet and fermentation produced chymosin preparations have received vegetarian certification.