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In 2012, a consortium of French scientists published a practical guide to raw milk microbiology aimed at farmhouse cheesemakers interested in fostering the natural microbial diversity of their milk. They show that healthy and stable microbial communities contribute to cheese safety (as evidenced by some of the research into the microbial biofilms on wooden boards used for aging Reblochon), and are also crucial to cheese flavour.
This short post introduces a simple test discussed within the book’s pages. It is quick and inexpensive, and can give a sensitive general indication of changes in raw milk quality without the need for expensive tests with an external lab: the lactofermentation test.
Many of the best raw milk cheesemakers keep a water bath on their kitchen counter and incubate a bit of milk each day as a matter of habit. Milk with a healthy predominance of lactic acid bacteria will rapidly set to a smooth gel, often within 24-36 hours at 22C. Milk that suddenly refuses to acidify or gel, or produces curd with small gas bubbles or a scrambled appearance, may be an early indication of a problem. The test often turns up issues long before they appear in the cheese (where the added starter cultures may obscure those same tiny changes in the milk’s microbial makeup).
The test is adaptable: it can also be used to monitor the hygiene of the milking machine and pipework (by pouring UHT milk through the clean system and then incubating it), to assess the microbial quality of the milk of individual animals, and to get a sense of a milk’s natural microbial flavor profile: does that naturally soured milk taste good? It’s a point that bears repeating: if a cheesemaker doesn’t want to taste the naturally soured raw milk that goes into his or her cheese, why would they want to serve the cheese made from it to their friends or customers?
The French textbook’s section on the lactofermentation test contains detailed instructions for carrying out the test and interpreting the results.
The English translation of the textbook was published in November, 2015, with a limited run of 550 copies, almost all of which were pre-ordered. A very limited number of copies remain. Please contact Bronwen Percival for more information.