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Raw milk cheeses: a valuable and diverse treasure with challenges for the future Page 1 / 7
Raw milk cheeses: a valuable and diverse treasure with challenges for the future
Extracts of the document: Les fromages au lait cru : un capital précieux et multiforme avec des enjeux pour l’avenir - Recueil de connaissances 2016
Authors: Florence Arnaud - Syndicat du Morbier, du Mont d’Or et du Bleu de Gex Haut-Jura, Pascal Berion – Université de Franche-Comté / UMR CRS 6049 ThéMA, Eric Beuvier – INRA de Poligny, Yvette Bouton – Comité Interprofessionnel de Gestion du Comté, Valérie Michel – Actalia, Eric Notz – Centre Technique des Fromages Comtois, Denise Renard – Comité Interprofessionnel de Gestion du Comté, Dominique-Angèle Vuitton – Université de Franche-Comté / EA 3181
Raw milk cheeses: a valuable and diverse treasure with challenges for the future Page 2 / 7
What is raw milk? What is a raw milk cheese?
Raw milk stands for natural untreated, animal milk that has not gone through pasteurization,
sterilization, thermization or micro-filtering. Raw milk is not brought to a temperature higher than
40°C, i.e. a temperature close to the temperature of the animal’s body. Consumption of liquid raw
milk nearly totally ceased in Western urban areas after pasteurization was discovered in 1864, but it
has remained steady in rural territories, especially in the regions where dairy farms are present.
A raw milk-cheese is a cheese prepared from raw milk. For years, and for some cheeses for
centuries, the microbial flora, i.e. the assemblage of microbes proper to raw milk (also called
‘microflora’, and now ‘microbiota’) has been exploited for its acidifying, proteolytic, lipolytic and
aromatic properties through specific regional craftsmanship transmitted from generation to
generation.
Empirically, the organisms present in milk have been used for milk preservation, including cheese
making. Raw milk-cheese making, following a deeply rooted heritage of diversity and complexity,
were and still are in absolute need of science inputs. As time went on, scientific progress has
highlighted the more precise role of the microbiota in cheese fabrication processes. First, it was a
matter of mastering cheese organoleptic quality by using microbial species with precise technological
and aromatic functions. Then, studies have focused into the sanitary level as well, in order to make
cheeses safely and with a constant level of quality. For the last past years, studies have taken interest
into understanding the complex biological phenomena which make possible that highly diverse
cheese production which is a unique heritage of our Western civilization. They have especially well
demonstrated that the final highly praised distinct sensorial properties of traditional raw milk-
cheeses and their associated microbiota came from each step of the milk and cheese producing
chain, from the flowers of the pastures to the environment of the ripening cellars, through the
unique ‘know-how’ of the cheese makers. They have also addressed the possible beneficial effect of
raw milk-cheese on health and diseases.
Raw milk, a factor of diversity for cheeses
Traditional practices used from milk production to ripening allow for particular flavours and
extremely different aromas between cheeses of a same type. This diversity of cheeses is due
especially to important variations in the initial microbial ecosystems of the various milks. These
variations in microbial composition lead cheese makers to technological adjustments. It is generally
accepted that these adjustments affect the general aspect of the cheese; but they also induce an
organoleptic signature specific to the dairy where the cheese was made. Richness and uniqueness of
each Protected Denomination of Origin (PDO) family of cheeses is generated thanks to the subtle and
infinite combinations of animal breed and mode of feeding, season, soil and flora of the pastures
(comprehensively included in the French word ‘terroir’), and fabrication processes. Original microbial
communities thus provide a unique sensorial diversity to raw milk-cheeses, as the outcome of a
complex and interactive process.
Raw milk-associated health benefits
An ability to limit the emergence of antibiotics- resistant strains of bacteria
Raw milk cheeses: a valuable and diverse treasure with challenges for the future Page 3 / 7
Results obtained by a consortium of French, Swiss and Italian cheese professionals and researchers
working at the University of Franche-Comté and at the National Institute for Agronomic research
(INRA) in the French Jura mountain area, have strongly supported the ability of raw milk-cheese
microbiota to survive in the intestine and to limit the occurrence of antibiotics-resistant bacteria
after a common antibiotic treatment, amoxicillin associated to clavulanic acid.
Prevention from allergies and from infections of the 1st year of life
An epidemiological study on allergy prevention and immunity by the rural environment, the
‘PASTURE cohort’, has involved a thousand families at the scale of 5 European countries for 16 years,
including Austria, Finland, France, Germany, and Switzerland. Allergy, i.e. asthma, atopic eczema, hay
fever, food allergy, constitutes a major public health issue which rapidly increased within the last 4
decades of the 20th century to reach more than 25% of the population today. As the number of
allergic patients is higher in cities, it was believed for long that urban pollution was at stake, as well
as changes in urban vegetal environment and population feeding habits. Yet, pollution is not but an
aggravating factor to these diseases; it does not increase the number of cases itself. Actually, and
conversely, studies performed in the 1990s highly suggested that the rural way of live, a countryside
living environment and, most importantly, the traditional style of life of dairy farmers, protected
from allergies.
To confirm that hypothesis, the PASTURE cohort has prospectively studied children since before they
were born. The 500 children born and living on a farm were compared to those 500 living in the same
rural areas but not on a farm. An enormous amount of data has been collected from the analysis of
samples of maternal milk and cow milk, of farm, carpet and mattress dust, of parents’ and children’s
blood as well as of the multiple questionnaires on children health and alimentation all along the
study. The study confirms unequivocally that life on dairy farms is an important factor of protection
against allergies. The earlier children are exposed to farming environment, including during their
mother’s pregnancy, the higher the positive influence. The main 2 factors of protection clearly and
consistently identified through the follow-up of this children cohort are the contact with animals (in
stables and barns: farm animals, and also dogs and cats), and regular consumption of raw milk – by
the infant but also by his mother during her pregnancy. Similar results have been obtained in other
studies with other designs, conducted in several other countries. “Drinking raw milk’ is a factor
distinct from ‘living on a farm’, and it applies as well to rural children not living on farms, and even to
children living in cities but sharing the same raw milk consumption. Consumption of dairy products -
like yoghurts, farm cheeses – was associated with protection as well. In addition, the PASTURE study
showed that infants drinking raw milk had less acute respiratory infections during infancy. It also
showed the importance of food diversification during the first year, and the influence of eating a
variety of cheeses during the first 18 months of the infant’s life. Overall, the concept of diversity
appears as a central idea from the results of recent studies, and so the necessity to preserve it comes
out scientifically reinforced.
Scientists keep on searching what raw milk and raw milk-cheeses bring up exactly in terms of
protection against disorders of allergic origin. An early encounter with microbes is important to
educate and train the immune system, and early changes in the immunological profile of the
protected children was demonstrated in the PASTURE study. Non-pathogenic organisms brought by
fermented products, such as cheeses, play a major role in this learning process since they are
Raw milk cheeses: a valuable and diverse treasure with challenges for the future Page 4 / 7
determining the quality of the intestinal microbiota (also called collectively ‘intestinal –or gut-
microflora’ or ‘microbiome’). These microbiota are composed of the billions of organisms – bacteria,
yeasts, fungi– present in the intestines and depend on what one breathes and eats
We now know that microbiota have multiple functions: in addition to immunological functions,
production of vitamins and fibre digestion, they have metabolic properties involved in the prevention
of obesity and cardiovascular diseases, and they even influence psyche, stress level and decision-
making… For all these functions, the diversity of microbial strains and species present in the intestine
is essential. Any alimentation favouring this diversity favours a balanced microbiome, and therefore a
balanced health status.
In addition to the role of organism biodiversity, the presence of immunomodulating factors and
distinctive lipids in raw milk, like omega-3 fatty acids in non-heated and/or homogenised milks, has
been associated with protection against asthma and allergies. A number of whey proteins, of
peptides with immunoregulatory properties, and of lipid components found in raw milk are
destroyed or highly modified, at various degrees, by the various modes of thermization. Recent
results from the PASTURE cohort have shown that children with the highest levels of the short chain
fatty acids (SCFAs) butyrate and propionate in faeces at the age of one year had significantly less
allergenic sensitization and were less likely to have asthma between 3 and 6 years; children with the
highest levels of butyrate were also less likely to have a reported diagnosis of food allergy or allergic
rhinitis. Such results are supported by experimental data. Further researches are necessary to assess
a possible responsibility of traditional raw milk-cheese consumption in triggering such effects.
Raw milk effects on inhibition of pathogenic microbes If the possible infection of some raw milk-cheeses by pathogenic microbes can be considered a
disadvantage in the food safety domain – to the point that the USA ban any importation of raw milk
cheese under 60 days of maturation – conversely, the microbial richness of a raw milk-cheese
protects it effectively against those hazards related to re-infection by pathogenic microbes all along
the cheese-making, ripening, and storage processes. Indeed, sterilizing milk before cheese
production can, because of the absence of competition between species/strains, paradoxically leave
the gates open for secondary infection by this type of pathogens, as suggested by the
epidemiological analysis of food-borne infections during the past 15 years which often involved
cheeses produced with heat-treated milk.
There is scientific evidence that the diversity of the microbial ecosystem of raw milk-cheeses such as
the French raw milk-cheeses Saint-Nectaire or Livarot may effectively counter the development of
pathogenic bacteria such as Listeria. Works from the INRA Unit in Aurillac, in the Massif Central area
of France, have shown raw milk potential for inhibiting pathogenic bacteria in semi-hard cheeses.
Other research works have demonstrated that an inhibiting effect towards Listeria monocytogenes
was operating when a complex biofilm was present on ripening shelves of the Reblochon cheese, a
PDO cheese produced in the French Alps. Using raw milk and certain traditional equipment, like
wooden vats or wooden ripening shelves, far from increasing risks of health hazards, guarantee a
lower risk, thanks to the inhibiting effect of certain non-pathogenic organisms. Indigenous microbiota
of very different compositions protect against Listeria monocytogenes inside cheese curd and at the
cheese surface. The inhibition seems to be associated with quantitative and qualitative composition
Raw milk cheeses: a valuable and diverse treasure with challenges for the future Page 5 / 7
of these microbial ecosystems rather than to their degree of diversity. Traditional cheese capacity to
limit the development of pathogenic bacteria is thus related to indigenous inhibiting strains or
microbial consortia. However, the mechanisms of inhibition have not yet been figured out exactly.
The mechanism may be biological – synergy, commensalism, or, on the contrary, antagonism or
competition. Natural non-microbial components of the milks play probably also a role in the process
such as temperature, hygrometry, oxygen level, or pH. It may also involve an association of several
factors. Depending on the case, bioprotection may rely on inhibiting elements (fatty acids, peptides),
on nutriments (present or absent), on physical or chemical modifications (acidity) and/or on
biological competitions (colonization).
A promising way towards understanding the inhibiting systems that are observed in practice consists
in isolating and simplifying the microbial ecosystems present in cheeses whenever the existence of a
protecting system is suspected. Then, the goal would be to identify practices that favour the
appearance of the identified ecosystem and/or to offer cocktails of selected strains capable of
reproducing its effects. Recently, the INRA Unit in Aurillac showed that it was possible to protect raw
milk-cheeses against the development of Shiga Toxin-like producing Escherichia coli by using
antagonistic bacteria throughout the development of two serotypes: O157 and most importantly,
O26, the prevalence of which is higher in raw milks.
Prevention of pathogenic hazards can rely on understanding and then application or preservation of
actions or mechanisms that have an inhibiting effect such as the sequential or simultaneous use of
temperature, water activity, pH, production of acetic acid, etc. Then, safety will not rely any longer
on the effectiveness of a single “barrier” but on mastering a succession of barriers. This proposition is
defined in the Codex Alimentarius as ‘the use of a combination of factors to control microbial
development’. However, our understanding of microbiota of technological interest must be explored
in more depth. New research techniques should eventually allow us to better understand the cheese
microbiota and make the link with the composition and properties of the human microbiota, a
domain with unprecedented expansion and fascinating developments. Understanding the
mechanisms behind the construction of cheese intrinsic characteristics, at the milk production and
cheese transformation levels, would make it possible to formalize the role and management
modalities of microbial ecosystems during this construction. Given the number of varieties of
cheeses, there is much to do, and funding such research remains an issue.
Traditional raw milk-cheese making as an asset to preserve
environmental biodiversity with societal added value.
Traditional raw milk-cheese making plays an important part into adding value to the dairy farming
and cheese making professions, into maintaining a lively agriculture in territories with difficulties,
into preserving employment and keeping landscapes open, into preserving the touristic
attractiveness of a variety of regions, and into creating social bonds in our modern society. The
studies conducted to reinforce connections between milk production and cheese transformation
allow all actors of the field involved in the cheese making process, producers, cheese makers and
ripeners, to share the same objective: producing high-quality cheeses, rooted in their territory.
Raw milk cheeses: a valuable and diverse treasure with challenges for the future Page 6 / 7
Particularly present in mountains and areas with geographic constraints, activities of production and
transformation of raw milk meet the expectations of a part of consumers which is getting bigger and
bigger, in European countries, in terms of the finished products themselves (the cheeses) and in
terms of their methods of production as well (sustainable agriculture). This change in consumers’
perception of the produces and modes of production includes, paradoxically, countries that were
defenders of pasteurization at any cost in the past, such as the USA. The dynamism and the
adaptation of producers to evolutions, internal just as external, lie in their capacity to offer high-
quality non-standardized products, based at the core on the proper management of microbial
populations all along the process of production and transformation. The microbial ecosystems
present naturally in the fabrication cycle of traditional cheeses are controlled and exploited through
the good practices that all actors at each level of the cheese-processing chain – breeders, cheese
makers, ripeners – have succeeded into maintaining and developing as time went on. Therefore, the
biodiversity naturally present in the various production and transformation environments eventually
finds its achievement in each cheese through the creation of its inimitable sensorial specificities. The
diversity of cheese characteristics, and the subsequent consumer’s pleasure, are thus the outcome of
the diversity of conditions of production and transformation of the milk, which are in turn part of the
consumer’s satisfaction.
Conclusion
Positive aspects of raw milk-cheeses are considerable. The benefits mentioned in this document
show the importance of maintaining a high biodiversity in cheese indigenous microbial communities
but also of maintaining the diversity of cheese fabrication practices which guarantee this microbial
diversity and the cheese quality. A great diversity of microbial metabolic activities, combined with
distinctive cheese fabrication methods, is crucial for the diversification of gustatory characteristics
specific to traditional cheeses; in addition it may be a very attractive leverage for reducing
pathogenic hazards.
The goal of searching for scientifically-based knowledge on raw milk-cheeses, and protecting their
mode of production, is neither to convert the entire cheese industry to using raw milk nor to
encroach on other types of production with their own economical and/or social logics. It is to
maintain and improve the quality of produces with high added-value – which we have seen to have a
lot of different impacts into many sectors of human activity, and that cannot only be accounted for
an alignment on the shelves of a supermarket.
A few questions should first be addressed, e.g.: What is the correlation between soil and cheese
microbiota? What is the health benefit directly related to the consumption of raw milk cheeses?
Studying the relationship between consumption of traditional cheeses and the intestinal microbiota
is likely a new and fruitful way to address the second question. The fast improvements in
metagenomic analysis and their easier and cheaper access should provide new data on the
microbiota of soil, raw milk, cheeses and of human gut. Combined with those on non-microbial
components of cheeses which could act as prebiotics, with measurements of the immunological
response and with the evaluation of the prevalence of diseases, these data should clarify the
relationship between health and consumption of raw milk-cheeses.
Demonstrating the risks associated with the consumption of raw milk-cheeses with a couple of food-
poisoning cases, with its emotional weight conveyed by the media, is relatively easy; estimating how
Raw milk cheeses: a valuable and diverse treasure with challenges for the future Page 7 / 7
this consumption has also “saved lives”, however, is far more complex and relies on long-term, less
emotional, evaluations. Isn’t sentencing raw milk cheeses to death with suffocating regulatory
pressure also a risk for public health in the middle- and long-term? It is essential that the weight of
regulation stays proportional to our scientific knowledge of risks, to a sound evaluation of the
risks/benefits ratio, and to the measure of the real pathogenicity of microbes originating from raw
milk and raw milk-cheeses for the populations. Loss of microbial biodiversity is, by definition, less
visible than loss of floral or wildlife biodiversity, but it may be just as serious.
Sanitary pressure from the last decades translated into a general impoverishment of the microbial
flora of raw milks. There are other ways of food processing than the hygienic strategy which consists
in “emptying, then replacing”: cultivating and supporting biodiversity all along the fabrication process
is a sensible alternative. The question of having a different approach to the microbial ecosystems is
worth asking. There is no question of advocating for a “backward step” and fostering permissiveness
when it comes to hygiene and infection. But the microbial ecosystems of milks are complex and their
balance subtle, not only a catalogue of microbes with single functions that can be put indifferently
next to each other. Finally, taking up on complexity will likely be the hallmark of the 21st century
scientific research, after the necessary simplifications that have been ruling over the 19th and 20th
centuries. Didn’t Pasteur himself – whom it would be pretty reductive to assimilate to pasteurization
– spend the best part of his life studying how complex microbial associations were contributing to
the quality of wines and beers? It is fortunate that new technologies of genomic characterization
finally make accessible an approach of microbiota that was still unthinkable until very recently.