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Dec 9, 2012 09:25 PM

Cheese: True (gut) Rennet vs. Microbial and other types...

Any comments on this?

Do you taste a bitterness in the finish of cheeses made with other types of rennet?

Ugh... I'm sampling a couple of cheddars and two were not made with authentic rennet.

Bleech... this weird bitterish flavor just hangs on my tongue.

The stuff made with real rennet is so much cleaner.

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  1. For the most part, I agree. Let's review the various types of rennet and how they contribute to cheese flavor. There are four categories of rennet:

    1. Natural rennet. This is what you called "real rennet." It is extracted from the abomasum (the "fourth stomach") of a young ruminant, i.e., a calf, a lamb or a kid, depending on the cheese. Calf's rennet is by far the most common. This is a complex rennet, consisting of a mixture of enzymes, the most important of which for coagulation of milk are chymosin A and chymosin B. Natural rennet also contains 10-20% pepsin, another enzyme.

    2. Microbial rennet. This is a somewhat vague term, since it is used, not only for this category but also sometimes for the next one. (See #3). Microbial rennet was developed to deal with the growing shortage of natural rennet. (The young animals must be killed in order to remove the stomach and prepare the rennet.) It also meets the requirements of vegetarians, who do not eat cheese made with natural rennet. Certain fungi (the most commonly used one is Rhizomucor miehei), secrete an enzyme that curdles milk in a similar way to natural rennet. The enzyme, however, is not the same as the chymosin found in natural rennet. Although improvements have been made to microbial rennets, they can still cause a cheese, especially a well aged one, to be bitter. I'm not surprised that you detected bitterness in some cheddars made with microbial rennet.

    3. GMO rennet. Modern genetic engineering has made it possible to insert the genetic material that codes for chymosin from a ruminant into a fungus, mold or yeast, which then begins to produce chymosin. The two most common microorganisms used for this purpose are the fungus Aspergillus niger and the yeast Kluveromyces lactis. This type of microbial rennet will not turn cheese bitter. However, the rennet is not as complex as natural rennet. The latter contains chymosin A, chymosin B, and pepsin, whereas GMO rennet is pure chymosin B.

    4. Vegetable rennet. Numerous plants yield substances that can be used to curdle milk. These include figs, mallow, nettles, lady's bedstraw and thistle, among others. Fig juice was used in ancient times, and lady's bedstraw was occasionally used in England in the 18th and 19th centuries, but today, there is only one vegetable rennet of commercial importance: the thistle, a close relative of the common artichoke. The rennet is a solution prepared from its flower pistils. Cheeses made with thistle rennet have a flavor all their own. The rennet results in a soft curd and the cheeses have both a slight bitterness and sourness. In thistle-renneted cheeses, unlike in microbial-renneted cheeses, the mild bitter overtone is considered a virtue and part of the normal flavor profile. Many cheese lovers especially prize these cheeses, which are a specialty of western Spain (province of Extremadura) and Portugal. They are traditionally sheep's milk cheeses, although there are now thistle-renneted cheeses made from cow's milk (Italy) and goat's milk (England).

    17 Replies
    1. re: cheesemaestro

      Great writeup man! Love it!

      I notice that many cheeses don't say "rennet" on the label. They just say "enzymes." Is it safe to assume that if the label doesn't specify the rennet type that it's either 2, 3, or 4 in your categories above?

      1. re: tangoking

        I think it is more likely that the type or rennet used is 2 or 3 rather than 1, although I wouldn't go so far as to say it cannot be 1, as the word "enzymes" covers all four types. It is less likely to be 4 because there are a limited number of cheeses made with thistle rennet.

        In my previous response, I should have said that the specific thistle plant used for making rennet is the cardoon. "Thistle" is a more generic term that encompasses numerous plants, including the cardoon and the artichoke.

        I am a bit disappointed that I am the only person other than you, as the OP, to participate in this thread. Perhaps people are not interested in the science of cheesemaking? There's a lot to learn about it, and knowledge of the basics is critical to any cheesemaker worth his or her salt. Even though I am not a cheesemaker, I have found that exploring some of the scientific and technical considerations has contributed greatly to my understanding and appreciation of cheese.


        1. re: cheesemaestro

          more that (for me, anyway) I never hear anyone talking about rennet. I'm assuming that most of the rennet in small-producer cheeses in Europe are animal rennet, but I really don't know, and don't know who to ask.

          This was more a "gee, I'll come back and read more when someone posts something" thread for me!

          1. re: sunshine842

            You are right that most farmhouse and artisanal producers in Europe won't use anything but natural animal rennet. Animal rennet is also indicated in the PDO specifications for some cheeses. Of course, many venerable European cheeses have been made for centuries and, through most of their history, animal rennet was the only kind available, except for vegetable rennets, which had limited use. The ever growing world demand for cheese and the rise of modern commercial cheesemaking operations led to the search for other relatively inexpensive ways to curdle milk; thus the development of microbial rennets, which are now in widespread use in Europe and elsewhere. If you buy cheese from a reputable cheese shop or from a local farmers market, people should be able to tell you what type of rennet was used to make a particular cheese.

            Also, since the OP asked specifically about bitterness from microbial rennet, I structured my response around the various kinds of rennet. I should add that there are numerous possible causes of bitterness in cheese, many of which have nothing to do with rennet. I could certainly elaborate on this statement, but, with so few people following this thread (at least that seems to be the case), I'm not sure this is the best time to do it. I will, though, if someone asks.

            1. re: cheesemaestro

              which is, then, the concern about a dedicated cheese board. :/

              This thread in particular is a zone in which I really can't add much to the discussion -- but I find it really, really interesting.

              1. re: sunshine842

                Yes, that is my concern. If Chow/CH gives us the green light for a dedicated board or a regular column, we will need to get beyond the kinds of threads that typically attract a lot of people, such as "I hate goat cheese"; "What's the best stinky cheese?;" "Can I freeze cheddar?". The variety of subject matter is extensive: individual cheeses and cheese categories, history, culture, science, production methods, animal breeds and milk types, storage, presentation, pairing with beverages and other foods, use in cooking, home cheesemaking, etc. The question is whether we have enough people who want to explore the full gamut, in the way that people who are passionate about wine and beer do on their respective boards. I certainly wouldn't want to answer that question based just on this thread, but the low number of posts did give me pause.

          2. re: cheesemaestro

            I just saw this thread and am fascinated! I knew about rennet and microbial rennt, but I have never heard of the other two.

            I've never made cheese, but I have seen it made in a few places. I think I may start with making fresh mozzarella, if I can find rennet.

            I love all kinds of cheeses, with maybe an exception of the maggoty one from Italy, that seems a bit off putting to me.

            1. re: cosmogrrl

              "the maggoty one from Italy"

              Ah yes, the infamous Casu Marzu from Sardinia. It can't be imported or sold in the US. It's also illegal to sell it in Italy, but it's still made and enjoyed by its fans in Sardinia. I've never had the pleasure (?), but I'm the type of person who could be goaded into trying it.

              If you can't find a source for rennet locally, there are several mail order options. I highly recommend The New England Cheesemaking Supply Co. in Massachusetts, run by Ricki Carroll. She sells both powdered animal rennet (expensive) and microbial rennet (much cheaper). Please note that what she calls "vegetable rennet" is not what I called vegetable rennet in my earlier post. It refers to microbial rennet. Her website,, is a goldmine of information about home cheesemaking, complete with recipes and anything else you can think of. She also publishes a monthly online newsletter, which she calls her Moosletter,. You can sign up to receive it. There are a few other online sources for rennet, which you should be able to find by doing a search on "cheese rennet." There have also been threads here on Chowhound about making mozzarella at home.

              1. re: cheesemaestro

                Corsica also has a "maggoty cheese" -- it's called casgiu merzu. I was told several years ago that it's alive and well, despite technically being illegal. I have a former colleague who married a Corsican, and bravely ate a piece when she first visited Corsica with her new husband, although she swore she'd never do it again.

                1. re: sunshine842

                  Both the Sardinian and Corsican names mean "rotten cheese." There's an alternate name in Sardinia, casu frazigu, which essentially means the same thing. The cheese isn't limited to these two regions. It's found under different names all over Italy--north, central and south. I particularly like the name in Friuli (a northeastern region): salterello, from saltare (to jump), obviously from the movement of the fly larvae.

                  The European Union has formally recognized the cheese as a traditional food. That hasn't stopped Italy from banning its sale. I assume that France also prohibits the sale of the Corsican version. However, my sense is that neither country has taken any steps to prevent those who are fans of the cheese from making and consuming it, as long as they are not also selling it.

                  I thought that the cheese had never made its way to the US, but a little research has proven me wrong. About a year ago, an Italian restaurant in Queens (New York City) was serving the cheese to customers willing to try it. The owner made it clear that he was not selling the cheese to them. (That would have been illegal.) How he got the cheese to New York is a mystery. It wasn't revealed in any of the articles I read. I can't imagine that he could have concealed such a strong-smelling cheese in his baggage, no matter how well it was wrapped, but who knows?

                  1. re: cheesemaestro

                    I cannot imagine -- he couldn't have vacuum-packed it, because it would have killed the larvae...

                    I can only guess at the smell -- I took a small round of Camembert and a small wedge of Brie to a friend in Miami last Christmas -- my regular fromager was closed for a family emergency, so I paid airport prices at the duty-free at CDG (not robbery, but definitely higher prices than my small-town fromager). It was in the retail packaging, and the clerk wrapped each piece in foil for me and gave me a plastic bag. I wrapped the bag in a sweatshirt (for thermal insulation) -- and by the time we got to Miami, yeegads. People were looking at me like they were wondering what died in my backpack.

                    So if Brie was that potent...I cannot imagine how bad the "cheese that comes to you" would smell.

                    (my fromager has just installed a spiffy new affinage case behind the counter...unfortunately, I haven't had time to go in and have him tell me all about it -- he's justifiably proud of it.)

                    1. re: sunshine842

                      A few cheese shops and cheesemakers in the US have built one or more artificial cheese "caves" for affinage. These are specially constructed rooms in which they can control temperature and humidity and keep out undesirable microorganisms. I've never heard of something as small as a a case serving that purpose. Is it something that is available commercially in France, or did your fromager build it himself? Once you find out more about it, I'd be very interested in an update!

                      1. re: cheesemaestro

                        It's stainless, with glass doors -- about the size of a large side-by-side refrigerator, so I'm guessing it's commercially available.

                        Hopefully he isn't taking the holidays off, so I can go let him tell me about it! If he lets me, I'll try to take some pics and email them to you.

                        I'm really quite pleased -- this guy started his own gig -- he's in his late 30s, and has already had to move to a bigger shop, and the line is out the door most days - and another fromager retired, selling his very busy stands at the marches to a couple in their early 30s, who are also bustling every minute of every market day. It's nice to see very young folks coming into the business and keeping it alive.

        2. re: cheesemaestro

          I especially love the Extremadura and Portuguese cheeses. They are so funky and complex. I think it's worth noting that it isn't any thistle, but the cardoon thistle, which is also grown for delicious stems (actually petioles) and as an ornamental plant and cut flower here in the US.

          There is also a short period (during WW2) when there was a rennet shortage in the british isles and they were coagulating the milk with snails. Which I've always wanted to try but don't know enough about the snails used to decide if our local variety would work.

          1. re: RockDoveFarm

            Thanks. I did note in a subsequent post above that the thistle in question is the cardoon.

            I believe that a species of black snail was used in the UK.

          2. re: cheesemaestro

            A couple of corrections to my original post:

            First, the vegetable rennet made from the cardoon thistle (#4) is prepared by steeping the flower stamens, not the pistils.

            Second, something bothered me about the last sentence of my post, specifically, that there is a thistle-renneted cow's milk cheese made in Italy. I had read that somewhere, and it surprised me, because I knew that previous attempts to create such a cheese resulted in a very bitter paste. The active coagulating enzyme from cardoon thistle, cynarase, causes unpleasantly bitter peptides to be produced when used with cow's milk. Upon further research, I've learned that the first article I read about the Italian cheese was wrong, and that the cheese is actually made from sheep's milk. The name of the cheese is Caciofiore (meaning "flower of cheese"). It's a firm to hard cheese, quite unlike the thistle-renneted cheeses from Spain and Portugal.

            1. re: cheesemaestro

              And yet. . . I've found numerous references to the flower pistils being used to prepare the cardoon rennet, which is what I originally thought. Perhaps both the pistils and the stamens contain the enzyme and so either can be used.

          3. The region of Western Spain and Eastern Portugal use mostly thistle rennet in products like Torta del Casar and Serra, similar products on different sides of the border. These, IMVHO, are as good as cheese gets and a small similar one called Azeitao is great as well.

            6 Replies
            1. re: Delucacheesemonger

              I'll have to look for that at my Portuguese grocery

              1. re: sunshine842

                Other Portuguese cheeses made with thistle rennet include Serra da Estrela (which Delucacheesemonger mentions), Serpa, Nisa and Evora. If you're not familiar with this style of cheese, I would start with either Azeitao or Serra. I also really like Amarelo da Beira Baixa, a mixed milk cheese (sheep and goat) that is made with animal rennet.

                1. re: cheesemaestro

                  this is doubly interesting -- I'm pretty comfortable with French cheeses, and quite a few Italian -- but the cheese case at the Portuguese grocery is largely unknown territory for me.

                  1. re: sunshine842

                    There is also a very nice firm cow's milk cheese from the Azores: São Jorge--very different from the other cheeses mentioned above. (I should have also spelled Azeitão with a tilde over the second "a." It indicates that the vowel is nasalized and pronounced much like the word "en" in French.)

                    1. re: cheesemaestro

                      Now that the holidays are over and the cheese cases are no longer heaped with foie and saumon and boudin (noir and blanc) and all the other holiday treats...and my fridge is not longer groaning under the weight of all the things at *my* house...I'll make a list and sally forth....

                      1. re: cheesemaestro

                        the Azores have so many amazing cheeses!

                        São Jorge is legendary, and Queijo São João and Queijo Picante da Beira Baixa are excellent as well.

              2. Really interesting information on rennet. I didn't know there were so many types.