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Are Flower Meadow cheeses made with untreated raw milk safe?

Wed, 05/19/2021 - 13:14
Blumenwiesen-Käse aus unbehandelter Rohmilch, Rotwein Bärger

The traditional production process guarantees that harmful bacteria do not survive.

The harmful bacteria are first paralyzed with cold, then boiled for at least 15 min, and the survivors are placed in an acid bath. This would not even survive Iron-Man

1. the milk is cooled down to approx. 10° max. 18
2. the curd is heated to at least 42° for at least 15 minutes
3. then the PH value is lowered to 5.3. This is achieved by the lactic acid bacteria breaking down the milk sugar lactose.


Dissertation by Hans-Peter Bachmann published https://www.research-collection.ethz.ch/handle/20.500.11850/141566

ZUSAMMENFASSUNG/RESUME/SUMMARY

Behaviour of potentially humanpathogenic bacteria of the genera . Aeromonas hydrophila, Campylobacter jejuni, Escherichia coli, Pseudomonas  aeruginosa,  Salmonella  spp.,  Staphy/ococcus aureus and Yersinia enterocolitica in semihard and hard cheese made from raw milk

Approximately 40 % of milk produced in Switzerland is processed to cheese without a prior heat treatment. This gives rise to discussions about hygienic safety of raw milk cheeses. The aim of the present investigation was to determine the risk in connec­ tion with the consumption of semihard and hard cheese made from raw milk. Of the following seven potentially pathogenic bacteria for humans, i.e. Aeromonas hydrophila, Campylobacter jejuni, enteropathogenic Escherichia coli, Pseudomonas aeruginosa, Salmonella spp., Staphy/o­ coccus aureus and Yersinia enterocolitica, 2 - 6 strains of each were chosen for the investigation. In order to assure a sufficient adaptation to the medium milk, a defined cultivation method was applied.

In the first part of the study, the resistance to some of the most important parameters in cheese manufacture (temperature, pH) was determined in order to select the most resistant strains of the above bacteria. Following · this, raw milk was contaminated with the selected strain (105 - 106 cfu / ml) and processed to cheese in an aseptic cheese-making system by observing specific safety measures. From each strain, 4 semihard (Tilsit type) and 4 hard (Emmental type) cheeses were made. The manufactur­ ing parameters applied for the cheeses were determined in the way to assure high quality as well as the longest survival of the potentially pathogenic microorganism. During manufacture as weil as the ripening period of 3 months, the potentially pathogenic bacteria were detected by two different methods.

With exception of S.aureus in two cases, none of the potentially patho­ genic microorganisms was found in the one day old hard cheese. All subsequent determinations were free from potentially pathogenic bacte­ ria and their toxins. In semihard cheese the potentially pathogenic bac­ teria were able to survive longer, but did not synthesise toxins. At the time of commercial ripeness the pathogenic microorganisms were in all cheeses below the detection limit.

The results of our investigations show that the hygienic safety of Swiss hard cheese varieties made from raw milk {Emmental, Gruyere, Sbrinz) under controlled conditions can be guaranteed with a high degree of certainty. Also the Swiss semihard cheese varieties made from raw milk (Tilsit, Appenzell) are, with faultless production, at the age of consump­ tion, with a large safety margin, free of potentially pathogenic bacteria and their toxic metabolites. lt has to be emphasized that the hygienic safety, along with the rheology and the sensory attributes, are elemen­ tary for a high quality of cheese and can be achieved entirely with a Good Manufacturing Practice. Finally, requirements in the manufacture of hard and semihard cheese made from raw milk were defined, in order to assure, with a high degree of certainty, that cheeses at time of con­ sumption are free from potentially pathogenic bacteria

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