Process Control

This Chapter will not be discussed during the short course lectures because most of its contents are covered in other Sections or in the cheese make procedures. It is included here as a summary of important process control principles.

The Objectives of Cheese Manufacturing

To maximize returns, the cheese maker must obtain the maximum yields which are consistent with good cheese quality. For example, water and salt are cheaper than milk fat and protein, but you can only have so much cheese moisture and salt---more on cheese yield in Yield efficiency. With respect to consistent production of high quality cheese the objectives of the cheese maker are to:

  1. Develop the basic structure of the cheese.
  2. Obtain cheese composition required for optimum microbial and enzyme activity during curing. Optimum composition mainly means optimum levels of moisture, fat, pH (lactic acid), minerals, and salt.

For example, the characteristic texture of Swiss cheese is largely determined at the time when the curd and whey are transferred to the press table. At this time the basic structure (i.e., the manner in which the casein micelles and fat globules are arranged) and chemical composition (especially mineral content) is already determined. You can not take Swiss curd at this stage and make Cheddar cheese. On the other hand it is possible to produce both Feta and a Brie type cheese from the same curd.

Moisture Control

  • cheese making is a process of removing moisture from a rennet coagulum or an acid coagulum consisting of fat globules (unless the milk is skimmed) and water droplets trapped in a matrix of casein micelles
  • cheese is, therefore, a concentrate of milk protein and fat.
  • most cheese making operations are related to this process of removing water from the milk gel by the process of syneresis
  • syneresis = to contract; refers to contraction of the protein network with the resulting expulsion of water from the curd
  • the water and water soluble components are literally squeezed out of the curd
  • this liquid, (whey) contains water, sugar, whey proteins, lactic acid and some of the milk minerals
  • the final moisture content, therefore, to a large extent determines the final pH of the cheese because it determines the residual amount of fermentable lactose in the cheese
  • at the same time other factors such as the amount and rate of acid development and the temperature and time of cooking, determine the amount and the rate of syneresis

pH Control

  •  with respect to cheese quality and safety, the most important process control factor is the development of acidity
  • increasing acidity causes:
    • syneresis (due to reduced charge repulsion on casein micelles) and moisture expulsion
    • solubilization of calcium phosphates
    • disruption of casein micelle structure with alterations in curd texture
    • reduced lactose content by fermentation to lactic acid
  • acid development occurs mainly within the curd because most bacteria are trapped in the gel matrix during coagulation
  • final pH (acidity) is dependent on the amount of acid developed during manufacture and the residual lactose which will ferment during early curing and cause further acid development
  • the residual lactose content is mainly determined by the moisture content, washing which removes lactose by leaching, and the extent of fermentation
  • ability of culture to ferment galactose is also important
  • both the rate of acid development and the amount of acid development (as measured by final pH) are important
  • eg., final pH of Swiss is the same as Cheddar but Cheddar cheese reaches pH 5.2 after about 5 hours while Swiss cheese requires about 15 h to reach this pH
  • it is important to maintain uniform rate of acid development; if acidity develops too slow or too fast, adjust the amount of culture rather than changing cooking time or temperature
  • pH at draining largely determines the mineral and residual sugar contents of the cheese and from the sugar, the final pH
  • salting reduces the rate of acid development, and, therefore, the time and amount of salting is important to the pH at 1 day and 7 days following manufacture. 

Mineral Control

  • loss of calcium phosphate determines extent of casein micelle disruption--hence it determines basic cheese structure; the important parameter is the ratio of Ca to casein or Ca to SNF which is easier to measure (See Table 1.1)
  • in Swiss (high Ca, about 750 mM Ca/kg SNF) micelle globular structure is intact while extensive dissociation and disruption of submicelles is evident in Feta types (low Ca, about 400 mM Ca/kg SNF))
  • retention of calcium phosphate in the cheese also increases the buffer capacity of the cheese
  • pH at draining determines the solubility of calcium and phosphate when the curd is separated from the whey
  • more Ca is retained at high draining pH as in Swiss cheese (pH 6.4 - 6.5) versus Cheddar 6.1 - 6.3 (See Table 1.1).
  • little Ca retained in Feta cheese which needs some explanation:

Feta is dipped into the forms early while the pH is still quite high. However, the moisture is also high because no cooking has taken place. Therefore, the moisture is removed by syneresis as the pH decreases while the cheese is in the forms. The net result is that a great deal of moisture (whey) is removed at low pH and most of the calcium phosphate is removed with it. This is also true for other soft ripened cheese like blue and camembert.

Texture Control

  •  untypical texture in a young cheese is a strong indication of probable flavour defects later; therefore, a primary objective of cheese making is to develop the ultrastructure which will determine the proper texture
  • conformation of the protein matrix is also influenced by pH--at lower pH micelles are disrupted, but the proteins are tightly packed because of reduced charge repulsion; therefore, Feta is brittle while Camembert is soft and smooth due to alkalinity contributed by ammonia during ripening
  • cheese drained at higher pH has higher calcium content and is firmer and more elastic
  • firmness is also affected by ripening agents (see 11.6 Flavour control)
  • other factors also play a role--salt, moisture, and fat, but none of these will alter the basic structure of the protein matrix at the submicellar level.

Flavour Control

  • milk heating and clarification treatments which determine non-starter bacteria present in the milk
  • types of cultures and coagulating enzymes
  • all cooking and curd handling procedures have specific effects on the types of ripening agents (bacteria and enzymes) which remain to ripen the cheese; especially in cheese such as Swiss where the composition and functions of the culture are more complex
  • pH at draining again important because it determines the distribution of plasmin and rennin between the curd and the whey
  • plasmin is the principal milk protease: it prefers neutral to slightly alkaline pH and is more soluble at low pH; therefore, cheese which are dipped at high pH have higher retention and activity of plasmin (eg., in Swiss protein breakdown during ripening is due to plasmin)
  • calf rennet is more soluble at higher pH but more active at lower pH; therefore, an acid cheese such as Feta or Cheshire, has more rennet activity than Cheddar
  • the solubility of microbial rennets is independent of pH