The early history of dairy bacteriology is reviewed from the point of view of milk as a vector for pathogens, spoilage of milk and dairy products, a fermentation substrate and the development of starter cultures. Joseph Lister, a Scottish surgeon, can be considered the founder of dairy bacteriology since it was he who isolated the organism we now know as Lactococcus lactis. Other important early contributors were the two Danes, Matthias Vilhelm Samuel Storch and Sigurd Orla-Jensen, the Frenchman, Louis Pasteur, the Swiss, Eduard von Freundenreich, and the Americans, Robert Breed, Herbert Conn, and Bernard Hammer.

Starter cultures are essential for the production of most cheese types. Since the late 19th century, starter technology has become increasingly sophisticated, evolving from use of undefined mixtures of species and strains to use of well-defined mixtures of strains sometimes with custom-designed properties. Most primary starters are composed of a few species of lactic acid bacteria (LAB) such as Lactococcus lactis, Leuconostoc mesenteroides subsp. cremoris, Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, and L. helveticus. Primary starters carry out acidification in the early phases of cheesemaking but also contribute to flavor and aroma. Other species (LAB and various bacteria, yeasts, and molds) are used as secondary starters and adjuncts, and contribute to ripening of many cheese types. This chapter provides a general introduction to starter culture systems, starter taxonomy and genomics, starter metabolism and its influence on cheese flavor and aroma, effects of bacteriophages, and strategies for starter preservation and propagation.

Cheese is the quintessential convenience food, which can be consumed as it is, without preparation, can be used as a sandwich filler, grated or diced and used as a condiment or as a component of several cooked dishes. An estimated 40% of cheese is used as an ingredient or component of other foods.

In this article, cheese as a vehicle of food poisoning is discussed, particularly the organisms involved, their sources, their infective doses, their growth during cheese ripening, and their control. It is concluded that ripened cheese is a safe product when it is properly made. However, soft cheeses have been responsible for food poisoning outbreaks worldwide. In cases where cheese has been incriminated in food poisoning, confounding factors including improper storage of the milk (no refrigeration for several days prior to manufacture), poor starter activity due to inhibition of acid production by phage and/or antibiotic residues in the milk, poor plant hygiene, gross environmental contamination, faulty pasteurization, shedding of the causative organisms by plant personnel, or different combinations of these factors are also often present. Biogenic amines are also discussed.

Smear or washed-rind cheeses develop an orange to red color on their surfaces during ripening, which is composed of bacteria and yeasts. For a long time, it was considered that Brevibacterium linens was the major bacterium on the surfaces of these cheeses. This organism was recently shown to be a mixture of two species, B. linens and the new species Brevibacterium aurantiacum. Both organisms produce pale yellow to deep orange or brown colonies, which are considered to be responsible for the orange to red color of the cheese. Several other new species of bacteria have recently been found on the surface of smear-ripened cheese including Arthrobacter arilaitensis and Arthrobacter bergerei, which were originally isolated from Reblochon and Camembert cheese, respectively, and Staphylococcus succinus subsp. casei and Staphylococcus equorum subsp. linens, which were isolated from a Swiss smear cheese made from raw milk. More recently, Agrococcus casei, Corynebacterium casei, Microbacterium gubbeenense, and Mycetola reblochonii have been isolated from different cheeses, including Livarot, Limburger, Gubbeen, Tilsit, and Reblochon. Their sources and their role in cheese ripening are also described.