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The Hidden World of Microbes in Raw Milk

Raw milk, once widely perceived as a risky and potentially dangerous beverage, is experiencing a renaissance as a potential health food. This shift in perception is primarily driven by the presence of natural, safe microbes that not only alter the flavour profile of milk but also offer potential health benefits by shaping the gut microbiome. Some argue that raw milk may even be safer than its pasteurised counterpart due to the competitive presence of microbes that can outcompete harmful pathogens.

This article, written by our very own cheesemaker and microbiologist, Sabrina Longley, explores the evidence behind these claims, allowing you to make an informed decision about whether raw milk is a product you'd like to consider. While raw milk remains a topic of debate, understanding its microbial composition and potential advantages can help you navigate this intriguing and polarising subject.

Raw milk, which has long been considered (and still is by many people) to be a highly dangerous product that is far too risky to consume, is now undergoing a re-branding of sorts, as many are now viewing it as a possible new health food. This is mainly due to the presence of natural microbes (the safe kind!) that could improve health by altering the gut microbiome and can alter the flavour profile of the milk to make it a more enjoyable product than its pasteurised alternative.

Some also consider raw milk to be safer than pasteurised milk, due to the presence of other microbes outcompeting the ones that could make you ill. In this article, I will explain the evidence supporting these theories, so you can make up your own mind if raw milk is something you would like to try!

In the US, the sale of raw milk is banned in 23 states, and the sale of raw milk cheeses has been strictly prohibited since 1949; only cheeses aged for more than 60 days are permitted to be sold (1). Here in the UK, raw milk cannot be sold in supermarkets or at all in Scotland, but elsewhere farms have opened up raw milk vending machines for general sale as long as they follow a set of safety regulations (2).

It is true that raw milk can transmit diseases by carrying pathogenic microbes such as Listeria monocytogenes, E. coli, or Salmonella, and if you do choose to drink it you may need to be more careful with how it is stored and where it has come from.

In fact, at Nettlebed Creamery, we pasteurise all the milk that we use for all our cheeses, our kefir, and also the bottled milk that we sell; this is due to the risk of the bacteria that can cause tuberculosis which is prevalent in the area where the cows graze. But it is also true that raw milk can contain many probiotic bacteria, and pasteurisation can actually remove or diminish some of the beneficial components of milk as well as removing pathogens (3).

Raw milk at it’s best will reflect the environment (terroir) that the cows are farmed; studies have confirmed that the microbial composition of milk can very depending on the time of year, weather, altitude, and location – the latter study, which concerned the differences in milk from different regions of South Korea, also found differences in the lipid, protein, and lactose content (4–6).

The unique microbial profile of the raw milk creates variation in the cheeses by creating slightly different fermentation products that will affect the flavour of the paste, and different microbes that will grow on the rind providing different appearance, textures, and flavours (7). Combined with differences driven by the weather and time of year, raw milk cheeses can vary from batch to batch, so if you are a big artisan cheese fan you may enjoy sampling the same cheese throughout the year and seeing if you can notice any differences.

So, what microbes do we tend to see in raw milk? The biggest group of microbes we will see is lactic acid bacteria (LAB), that we have previously discussed in the context of cheesemaking. These are the bacteria, generally species from the genera Lactobacillus and Lactococcus, but also Enterococcus, Streptococcus, and Leuconostoc, that will ferment the lactose in milk into lactic acid, dropping the pH and allowing the milk to curdle in a way that can create cheese, yogurt, kefir, and cultured butter whilst also creating aroma and flavour compounds that will influence the taste of the resulting product (7).

The reduction of the pH of the raw milk by LAB will also create an unsuitable environment for the growth of harmful bacteria and can actually make it safer to drink even without refrigeration, as well as also having an antimicrobial effect directly on pathogenic bacteria (an argument against the use of pasteurised milk states that it can actually be less safe to drink due to the lack of competition from other microbes that can allow harmful bacteria, such as Listeria monocytogenes and Salmonella to grow) if poor hygiene in the dairy leads to post-pasteurisation contamination with any of these pathogens (3). At the Nettlebed Creamery our strict hygiene procedures are in place to prevent this!

Many species of LAB are also thought to be probiotic bacteria, and so consumption of raw milk can be beneficial for your gut microbiome (8); in fact, a study published in 2020 found that regular consumption of raw milk over a 12 week period resulted in increases in Lactobacillus populations in the gut microbiome, and this coincided with significantly reduced anxiety scores in those who had been experiencing high anxiety at the start of the study (9).

Additionally, they found an increase in the volume of valerate produced in the gut – this is a short chain fatty acid that is produced by gut bacteria and is thought to have a role in increasing immune function, and it was deduced that this increase had been brought about by the increased populations of Lactobacillus. Also found in raw milk are the fungal microbes, including the yeasts Saccharomyces and Kluyveromyces; their metabolism may also create fermentation products that can influence flavours and aromas in the cheese (10).

Not all of these fungal microbes are desirable however, for example, a common mould found in raw milk is Penicillium commune which can lead to the development of blue mould on the rind of cheeses which is considered undesirable due to it’s unpleasant appearance (10). All in all, these microbes create a complex ecosystem inside raw milk, not unlike that which we see in kefir, that can be very beneficial for your gut (9).

In conclusion, raw milk contains a whole world of microbes within it, which can work towards creating vast differences in the taste of fermented products as well as potentially supporting your health via the presence of probiotic bacteria. However it must be said that caution must be taken when consuming raw milk or raw milk products to ensure it is from a reputable source as it is considered less safe than pasteurised milk. Those who are 65 or over, pregnant, immunocompromised, or young children should not consume raw milk or raw milk products.


1. Raw Milk State Laws and Regulations | Real Raw Milk Facts [Internet]. [cited 2023 Oct 6]. Available from:

2. Raw drinking milk | Food Standards Agency [Internet]. [cited 2023 Oct 6]. Available from:

3. Reuben RC, Roy PC, Sarkar SL, Rubayet Ul Alam ASM, Jahid IK. Characterization and evaluation of lactic acid bacteria from indigenous raw milk for potential probiotic properties. J Dairy Sci [Internet]. 2020 Feb 1 [cited 2023 Oct 6];103(2):1223–37. Available from:

4. Seon Kim I, Kyung Hur Y, Ji Kim E, Ahn YT, Geun Kim J, Choi YJ, et al. Comparative analysis of the microbial communities in raw milk produced in different regions of Korea. Asian-Australasian J Anim Sci [Internet]. 2017 Nov 1 [cited 2023 Oct 6];30(11):1643. Available from: /pmc/articles/PMC5666200/

5. Bonizzi I, Buffoni JN, Feligini M, Enne G. Investigating the relationship between raw milk bacterial composition, as described by intergenic transcribed spacer-PCR fingerprinting, and pasture altitude. J Appl Microbiol [Internet]. 2009 [cited 2023 Oct 6];107(4):1319–29. Available from:

6. Li N, Wang Y, You C, Ren J, Chen W, Zheng H, et al. Variation in Raw Milk Microbiota Throughout 12 Months and the Impact of Weather Conditions. Sci Reports 2018 81 [Internet]. 2018 Feb 5 [cited 2023 Oct 6];8(1):1–10. Available from:

7. Coelho MC, Malcata FX, Silva CCG. Lactic Acid Bacteria in Raw-Milk Cheeses: From Starter Cultures to Probiotic Functions. Foods 2022, Vol 11, Page 2276 [Internet]. 2022 Jul 29 [cited 2023 Oct 6];11(15):2276. Available from:

8. Zielińska D, Kolozyn-Krajewska D, Laranjo M. Food-Origin Lactic Acid Bacteria May Exhibit Probiotic Properties: Review. Biomed Res Int [Internet]. 2018 [cited 2023 Oct 6];2018. Available from: /pmc/articles/PMC6191956/

9. Butler MI, Bastiaanssen TFS, Long-Smith C, Berding K, Morkl S, Cusack AM, et al. Recipe for a Healthy Gut: Intake of Unpasteurised Milk Is Associated with Increased Lactobacillus Abundance in the Human Gut Microbiome. Nutrients [Internet]. 2020 May 1 [cited 2023 Oct 6];12(5):1468. Available from: /pmc/articles/PMC7285075/

10. Lavoie K, Touchette M, St-Gelais D, Labrie S. Characterization of the fungal microflora in raw milk and specialty cheeses of the province of Quebec. Dairy Sci Technol [Internet]. 2012 Sep [cited 2023 Oct 6];92(5):455. Available from: /pmc/articles/PMC3478505/

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