Reading the title we might ask ourselves: “If cheese making is a method of preserving milk, why should preservatives be added to cheese?”
Fresh food by its nature is subject to chemical and physical alterations if not properly stored. Man has always tried to fight food deterioration with processes such as cooking, salting, drying, smoking and other methods of preservation.
Since the nineteenth century, with urbanisation and the migration from the rural areas into the cities, food processing became a need, as far as the distances between the “place of production” and the “place of consumption” increased. At the same time much progress was made in the food industry thanks to many scientists e.g. Pasteur
Contamination of milk and pasteurization
Alteration of food might be caused both by biological and physical factors, often related to each other.
Biological causes are related to microorganisms and enzymes present in the food itself, while chemical and physical ones are triggered by contact with external agents such as oxygen, light, heat, humidity and so on.
In cheese making there are many sources of contamination.Milk might reach the dairy already contaminated: it might be contaminated in the stable, in the milk truck, in the dairy itself. For this reason cleaning in all phases is essential.
In addition to cleaning, also temperature control is very important: milk must be immediately cooled in order to stop the development of the microorganisms, especially when it is processed or collected the day after milking.
The greater the distance between the stable and the dairy the greater the time of “preservation” of milk and therefore the risk of contamination.
Dairies that collect large quantities of milk must obviously deal with long transportation times. Moreover the milk comes very often from different barns, where cows are fed with different feeds and treated under different hygienic conditions. In this situation, in order to obtain a safe product, it is better to pasteurise milk.
But sometimes it might not be enough.
Feeding of cows and formation of harmful microorganisms (clostridia)
Pasteurisation kills most of the harmful microorganisms, such as Salmonella, Listeria and Escherichia Coli, but under particular environmental conditions some microorganisms such as Clostridium produce spores (a kind of protective capsules) that survive for years.
These spores resist both to the digestive system of cows, to pasteurization and to the most common disinfectants ; when conditions turn to be favorable they start back germinating and, in absence of oxygen, harmful microorganisms begin to reproduce.
These microorganisms feed on sugars (lactose) or amino acids - depending on the species - and produce gas, generating abnormal swellings in cheese. Swellings are “precocious” when generated by microorganisms that feed on sugars and “late” when generated by microorganisms that feed on amino acids: these may occur also after 12 months of maturing. Usually swellings affect not only the appearance of cheese but are associated also with organoleptic defects, such as unpleasant smells and tastes.
As we have already said, the feeding of cows plays a fundamental role in the composition of milk. The same works for its microbiological characteristics.
Feeding cows with silage (fermented fodder stored in the absence of air) is the main cause of clostridia in milk: with traditional feeding, based on grass or hay, there are on average less than 200 clostridi spores per liter of milk, whereas when cows are fed with silage the average number of spores per liter grows to more than 2.000.
Silage is used anyway because it allows the reduction of the costs of the “ration”. The unifeed is a “single course” that allows to hand out at once all the components of the diet mixed together, with a significant saving of time. Large mixers are used to take silage from silos, add the forages and mix them with cereals and other raw materials, even liquids. The problem with this system is that dust and earth that contaminate the forage end up in the mixture and the presence of water, starches and sugars fosters the development of clostridia; the cows ingest the spores; feces and sewage are spread like organic fertilizer, bringing the spores back to the ground, so that the clostridia proliferate and the cycle starts again. Moreover poor sanitary conditions in the stable inevitably lead to high amounts of microorganisms and spores.
The presence of spores in milk can be reduced through the outcrop of the cream - when the technology requires it - but if the spores are present in very large numbers it is not enough.
Moreover, in cheese making, the use of a good whey starter, a correct cooking and drying of the curd (operations that lead to a quick and optimal acidification) can partly prevent the development of the spores, but sometimes it might be necessary to resort to the use of an additive, lysozyme.
E1105 - Lisozima
Lysozyme - described for the first time in 1922 by Alexander Fleming - is a protein naturally present in some biological secretions (e.g. saliva, tears, nasal mucus, milk) and in chicken eggs (albumen contains large quantities of lysozyme).
It has a strong bactericidal action, not by chance it is abundantly secreted in the body regions most exposed to contact with pathogens (e.g. oral cavity). Lysozyme attacks some types of bacteria, such as Clostridium tyrobutyricum (responsible for the late swelling), destroying the cell wall.
In the food industry lysozyme is generally obtained from egg white, it is identified with the acronym E1105 and is classified into the category of preservatives.
Lisozyme is usually added to milk in the production of aged cheeses, to prevent the development of clostridia and avoid possible “late bloatings”. It must always be declared on the label for two reasons: because it is added as an additive; because, since it is obtained from eggs, it could give rise to allergic phenomena.
In addition to Lisozyme, other preservatives are used in cheese making, such as Natamicina (E235) and Sorbic acid (E200), which are added to the cheeses for preserving the surface.
E235 - Natamycin (called also Pimaricin)
Natamycin (or Pimaricin E235) is an antifungal antibiotic used for the surface treatment of extra hard, hard and semi-hard cheese, to prevent the formation of mold. It can be applied by immersing the cheese in the disinfectant solution or by spray.
It should not be found 5 mm below the surface, this is why on the label of cheeses treated with Natamicina there is often the indication “rind not edible”. However, if the crust is thinner and this preservative has been used on the cheese, it is advisable to remove a bit of sub-crust before consuming the product.
E200 E202 E203 - Sorbates
Sorbates (E200, E202, E203) are mainly used as antimicrobial preservatives. In watery acid solutions they dissolve easily and they convert into sorbic acid, which has a marked activity against mold and yeast. For this reason sorbates are used to prevent the development of molds on the surface of hard and soft cheeses and dairy products (e.g. ricotta).
Obviously foods must be safe, but sometimes accepting few aesthetic imperfections would give us the possibility to decrease the amount of additives that we introduce with our diet.
Feeding, hygiene, short supply chain: these are the key strategies for avoiding preservatives in cheese. One more reason to support small producers who work in their own dairy the milk of their own animals.