Types of Coagulants for Cheesemaking
By Vicki Dunaway
Despite sustained efforts to find replacements, most cheesemakers still regard animal rennet as the gold standard. War, competing uses for abomasa, and the rise of vegetarian/vegan/animal rights issues have all spurred research and development on alternate coagulants. Some efforts have been more successful than others. During his cheesemaking adventures, Kosikowski found a very unusual response to the vegetarian dilemma in India, where calf slaughter is prohibited: they (scientists, I presume) have tried boring a hole (fistula) in the side of live calves and extracting excreted rennet at feeding time.[i] Seems a bit desperate to me, but illustrates the high value of calf rennet.
Coagulating substances obtained from plants were probably the earliest alternative “rennets” and are what you would call true vegetable rennets. There’s a surprisingly long list of plant-based coagulants available, including:
Achillea millefolium: Yarrow
Ananas sativa: Pineapple
Articum minus: Burdock
Carica papaya: Pawpaw (papain)
Carlina spp.: Alpine thistle
Centurea spp.: Knapweed
Cirsium spp.: Common thistle
Cynaria cardunculus: Cardoon
Dipsacus sylvestris: Teasel
Euphorbia lathyrus: Spurge
Ficus carica: Fig
Galum verum: Lady’s bedstraw, cleavers
Herculeum spondylum: Hogweed
Malva sylvestris: Common mallow
Ranunculus spp.: Spearworts
Ricinus communis: Castor bean (poisonous)
Senecio jacobea: Ragwort
Solanum dalcamara: Bittersweet
Solanum dobium: Jubein
Urtica diocia: Nettle
Withania coagulans: Withania berry
Each plant-based coagulant is different and they are used in different ways. Cardoon, for example, is made using an aqueous extract of the flower—this particular enzyme is a requirement for the production of Serra da Estrela cheese of Portugal. On the other hand, the latex (sap) of the fig tree is used for coagulation. Fortunately, we are now able to search the internet for instructions on how to prepare and use these obscure coagulants. Below are instructions for making an extract of cardoon, from the legendary Artisan Cheesemaker website of James Aldridge. [ii]
The plant “cardoon” naturally produces an enzyme (Cardosine A) which will coagulate milk. This is a true vegetable coagulant and is used by most artisan cheesemakers in Portugal. It is a member of the artichoke/thistle family. The flowers are plucked and dried then infused in warm water into a tea which is then used in the same way as one would use rennet: I usually use around 25 grams of dried flowers, twisted into a bag of cheesecloth, to a large cupful of warm water. I am not sure that it would be suitable for a cheddar-type cheese as it produces a more delicate set and, in my experience, seems to be rather more proteolitic [sic] than rennet. It has a quiet [sic] different life about it and it needs a perceptive person to work with it. (The amount you use will vary for many reasons … try 5 ml. of the mixture per liter of milk as a jumping in spot.) It grows fine in the U.K. and is perennial.
With the cost of animal rennets up and availability down, porcine (from pigs) pepsin has been mixed in with animal rennet to make it go further. Pepsin alone can cause bitterness and is slow to coagulate fresh milk. Porcine pepsin loses some of its unwanted proteolytic activity at high temperatures and so may be more suitable for cheeses that require a high-temperature scald. One study cited by Scott found that cheese made with pepsin had a more open structure than that made with calf rennet.[iii] Pepsin can also be extracted from cattle, sheep, and chickens, though this is not practiced widely.
Microbial Rennets and Recombinant Chymosin
There is a lot of confusion about natural microbial rennets and those produced by genetic recombinant (GMO) techniques. Both are sometimes referred to as “microbial rennets,” but they are entirely different. One also hears them called “vegetable” rennets, but neither has anything to do with vegetables. Both, especially the GMO ones, are often used for so-called vegetarian cheeses.
Particularly during and after World War II, there was a strong interest in finding rennet substitutes produced by bacteria and fungi. Species of mucor, endothia, bacillus, and even the mushroom russula all were investigated and found to produce enzymes that coagulate milk; some have been made into commercial products. Early versions often resulted in bitterness, hard curds that lost fat in the whey, curd shattering, high proteolysis, and/or other problems. Newer formulations exhibit greater purity with fewer problems; they are also sometimes blended with pepsin or calf rennet. Mucor miehei coageulants were successful, with a lower incidence of causing bitterness than some of the others. Marzyme is an example of a true microbial coagulant.
Recombinant chymosin is produced by microbes into which have been inserted the gene for production of prochymosin. The gene is transferred from calf abomasum tissue to one of several microorganisms, including Escherichia coli K-12, the yeast Klyveromyces lactis or the fungus Aspergillus niger. The microbes produce prochymosin, “followed by fermentation, cell destruction, activation of the pro-chymosin to chymosin and harvesting/producing large yields of 100 percent chymosin.”[iv] According to Kosikowski, “This genetic product, transferred from an animal, is considered a plant product, as microbes are of the plant kingdom.” (I’m not so sure this is true anymore — I think bacteria and fungi have their own kingdoms now.)
Recombinant chymosin is pure chymosin and has few of the problems of the natural microbial coagulants. It is available in single and double strengths, and one is even blended with pepsin to mimic natural rennet, which contains a small percentage of pepsin. Brand names with production organisms include: Chy-Max (E. coli K-12), Chymogen (Aspergillus niger var. awamori), ChymoStar (Aspergillus niger var. awamori), and Maxiren Kluveromyces marxianus var. lactis).
My strong favorite of rennet types is animal rennet, not because I like the thought of killing baby animals, but because it is the only type made (more or less) in the traditional way. The existence of all of the others is utterly dependent upon the laboratories of multinational corporations. If those labs closed tomorrow, there would be no more “vegetarian” rennet (other than the plant-based types). While I recognize that most of the commercially available animal rennet is also made in these labs, there is nothing preventing me from making my own.
Traditionally young ruminants — especially the useless males (sorry, guys) that would otherwise spend their time consuming scarce resources and butting heads — have been slaughtered for meat soon after birth. This is a worldwide practice born of necessity and is incorporated into many spring festivals, where the meat is a central feature of the celebration. Young goats, lambs, and calves provide high-quality protein at a time when other foods may be scarce in the natural cycle of things. Less “civilized” societies do not waste as we do — they use every part of the slain animal, and rennet is a highly valuable by-product. We should celebrate it.
[i] Frank V. Kosikowski and Vikram V. Mistry, Cheese and Fermented Milk Foods (Westport CT, 1997), p. 388.
[ii] Now located at http://www.isleofmullcheese.co.uk/jalldridge/jaindex.htm
[iii] R. Scott, Cheesemaking Practice (Gaithersburg MD, 1998), p. 161.
[iv] Kosikowski, p. 394.
Vicki Dunaway was formerly an artisan cheesemaker and editor of CreamLine and Home Dairy News.
Originally published in the September/October 2014 issue of Dairy Goat Journal.