Principal Ripening Agents
- Plasmin: A milk protease which survives pasteurization and breaks down caseins during cheese ripening.
- Particularly important in Swiss type cheese.
- Inhibited by Beta-lactoglobulin, so it has minimal activity in cheese made from ultrafiltered milk.
- Lipoprotein lipase is the principal milk lipase
- Inactivated by low heat treatment but is important to flavour development in raw milk cheese
- Each milk coagulant has its own proteolytic profile (see section on coagulants).
- Purified extracts produce more consistent flavours but lack character.
- For aged cheese no enzyme other than calf rennet and recombinant calf rennet has proven fully acceptable.
- Rennet and recombinant rennet actively break down alpha-casein but do not break down beta-casein in cheese.
- During the early days and weeks of ripening, LAB numbers decrease while the numbers of nonstarter bacteria decrease. For example, in Cheddar cheese, LAB counts reach a maximum (up to 500 million per gram) within 3-4 days and then decrease to about 20 million at 4 weeks. However, the dying cells release enzymes which continue to ripen the cheese.
- Lactic cultures contribute to proteolysed flavours but are minimally lipolytic
- Heterofermentative cultures ferment citrate as well as lactose and contribute both flavour (diacetyl) and carbon dioxide for small eye development
- In Swiss types, carbon dioxide production by Propionibacterium is encouraged by exposure to 200C for about 3 weeks after brining and drying off in the cold room.
- For smear ripened cheese, Brevibacterium linens , coryneform bacteria, and yeasts are encouraged by high humidity (90-95%) and washing to discourage moulds
- Penicillium sp. for Camembert, Brie and Blue types require 85-90% humidity and air circulation to provide oxygen
Microorganisms present in the milk due to environmental contamination are important contributors to milk ripening. Some important facts are:
- Bulk cooling and storage of raw milk selects for cold tolerant (psychrotrophic) bacteria (see Process and quality control procedures).
- Heat treatment selects for thermal stable spore forming bacteria
- Non-starter bacteria commonly present in heat-treat Cheddar include Lactobacillus sp. and Pediococci sp.
- Many other bacteria and yeasts may be present and may or not grow depending on complex symbiotic relationships with other bacteria.
- Heat treat is really a process of standardizing the nonstarter microorganisms, namely, eliminate proteolytic psychrotrophic bacteria but retain a range of useful ripening microbial agents.
- Non-starter bacteria in cheese milk can be reduced by microfiltration.
Added Ripening Agents
Addition of lipases as noted earlier is common for Italian and other cheese varieties. The principal areas of continuing development are:
- Accelerated ripening agents for all ripened cheese, especially Cheddar
- Ripening agents for low fat cheese, again especially Cheddar.
- The principal approaches are:
- Direct addition of single enzymes of dairy or non-dairy sources
- Enzyme cocktails which are mixtures of proteases and lipases. Other than in the preparation of enzyme modified cheese pastes, enzyme cocktails have had limited commercial success.
- Enzyme capsules which release trapped enzymes during ripening.
- Attenuated (freeze shocked or heat shocked) proteolytic cultures
- Genetically modified cultures hold lots of promise for future success.
- Culture adjuncts such as Lactobacillus helveticus in Cheddar cheese hold much promise to replace the normal diverse microflora of raw milk.