Collagen conversion - what is the threshold temperature?

Trying to solve a culinary riddle here: ultimately, I am trying to figure out if low temperature actually converts connective tissue (collagen) to the good stuff (gelatin), or if not, what is the effect of doing a long, low cook (e.g. 72-hour short ribs)

The venerable team at modernist cuisine says that collagen begins to convert to gelatin at temperatures as low as 122F - looking elsewhere on the web, I see temperatures for denaturation of collagen (which, if I undersand it correctly, is the precursor to shrinkage, which leads to creation of gelatin) starting at higher temperatures, closer to 140F. In this forum, it is mentioned that it happens at 130. Who is right?

Prior post on temperature and collagen conversion
http://forum.chefsteps.com/discussion/1268/tough-old-venison-sousvide-time-temp

Study on bovine IMC (collagen)
http://www.animal-science.org/content/69/5/1989.full.pdf

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Comments

tshewman

I suspect a bit of a complex answer. Why collagen (some) can begin at 122F, my understanding is this depends on the animal, involved region and tissues (think what muscle is it, what is the muscles composition and is it attached to anything-like bone-or anything else that impacts heat conduction. To get collagen from bone, I recall a paper that suggested it becomes soluble at about 136F. This is sort of an example on why we need more information when we consider time and temp. IMHO.

Brendan_Lee_56950

Just like most things in the kitchen, it's an interaction of temperature and time. The lower the temperature goes, the longer the time needs to be to achieve the same result.

There are many different kinds of collagen (five is the common number I think) and they all behave differently. This also depends on the type of animal, breed, etc, so the scientific answer is "it depends". This is a similar conversation that is had when discussing Maillard reactions. They may occur very rapidly at 250F but in reality happen at a wide range of temps as long as you are willing to put in the time. Collagen is the same way, if you want a juicy, tender product and are willing to put in the time you can drop the temp and go low and slow and get amazing results.

Chris_Young_80640

The transformation of collagen into gelatin does not happen at a particular temperature. Modernist Cuisine says that it happens as low as body temperature, but when I wrote this I did not mean to imply that this is a "threshold" temperature. Actually I went out of my way in the meat chapter to explain that nearly all cookbooks, and even a few meat science books, are wrong in this regard.

The underlying chemical reaction follows first-order Arrhenius behavior, which simply means that as the temperature goes lower it will take longer for this chemical reaction to occur. At some point, it doesn't even appear to be occurring. And this is where I think the misunderstanding comes from in the kitchen.

At 150 °F or so, it appears to be happening quickly, taking minutes to a few hours to go from tough to tender. So people say that collagen denatures at 150 °F. Or 145 °F, or some other similar temperature.

But during life, collagen needs to be replaced in our muscles, and so the reaction is occurring at body temperature. But now it's on the order of hours and days. In theory, it will happen at even lower temperature but the time will become much, much longer. To the point where it doesn't even seem to be happening.

adam_k_17574

Thank you for the response - can you help me understand the chemical process a bit better? There is often talk about denaturation of alongside conversion to gelatin, but if I understand the process correctly, these are two different points on a curve. Denaturation happens at a lower temperature and continues up to the shrinkage temperature, where heat has essentially denatured the sh*t out of the protein. From what I am reading, hydrolysis appears to happen after the protein has hit the shrinkage temperature.

This is what I mean about a threshold or a inflection point where denaturation results in hydrolysis/creation of gelatin. Denaturation happens at all temperatures (even freezing), and is apparently affected by things like pH, type of protein or collagen, but bovine IMC seems to have some observable temperature range (shrinkage) where the magic happens.

This is one of the studies I was looking at that shows collagen shrinkage happening above 60c. Here is another source I was using for info.

adam_k_17574

I should have asked specific questions in the post above - more to the point:

Is shrinkage temperature significant in the production of gelatin? If it is, what is happening to collagen up to that point?

Thanks in advance!

Chris_Young_80640

@Adam.k

There are several reactions that need to occur, one after another, to convert collagen into into gelatin. Hydrolysis is one of those. So far as I know, all of these follow first-order chemical kinetics. So saying that the lower you go, the longer it takes remains true of the overall transformation. Certainly there is an inflection point in each curve, and it will depend on the reaction conditions (pH, etc) as well as the type of collagen and the degree to which it is cross linked.

Shrinkage is a bulk phenomenon that emerges from the average of what all of the collagen fibers are doing. If you cook the meat at lower temperatures, fewer of the collagen fibers shorten at any given point in the cooking process, so the overall collagen mesh constricts the meat less. So you observe less shrinkage. This is why meats retain more of their juices when cooked sous vide or by other slow-cooking processes. But at lower temperatures more time is needed to shrink, unravel, and dissolve enough of the collagen fibers to make the meat pleasantly tender.

So the short answer is that significant shrinkage is not required to produce gelatin, if you are willing to go slower.

Maan_61028

Maybe this is late but I spent all morning today getting the nuts and bolts for collagen to gelatine conversion, and its not that easy specially as Chris pointed out correctly and spot on that there is no activation temperature as its first-order unimolecular reaction that involves a single molecule which in other words a degradation process, according to the physics of it at higher temp only the reaction rate increases and it's not where the reaction starts, the reaction is happening at room temp but at very slow rate and once again Chris points out correctly thats why we need to replace our collagen in our bodies because our collagen is degrading but at very low rate due to temp compared to cooking temp, so the activation energy and temp are independent of each other, but temp is closely related to the reaction rate.

For the shrinkage effect its a different matter as its a collective effect (bulk effect) of the denaturing process of all proteins found in the meat and not only collagen, collagen toughness is represented by the muscle fibres and their density, not all muscles have the same amount of collagen because some muscles don't need it like a chicken breast compared to the drumstick, but yet all muscles shrink almost at the same rate so its a collective effect.

Sous vide reduces the collective shrinkage effect to very low levels and in doing that you supply enough temp to increase the collagen-gelatine conversion rate.

Diablote_389234

This is the riddle in the alchemy of turning muscle into meat. Per all my resources, collagen shrinkage does not start below 140˚F. My BBQ/slow cooker references all claim that 160˚ is where collagen starts to break due to contraction, with a peak at 180˚. The Science of Good Cooking in particular shows through experimentation that the collagen in oxtail turns into form-holding gelatin after 3 hours at this range. Smoking recipes for pork shoulder and beef brisket almost all call for cooking to 195-203˚, which I can only surmise is because that range is where all the collagen has been above 160˚ for about 3 hours in a 250˚ smoker.

As you note, shrinkage cannot be the only means of collagen to gelatin conversion. It is enzymes that degrade it at lower temperatures. Most sous vide sources claim cathepsins in particular are the primary conversion mechanism below 140˚. The Science of Good Cooking shows a beef rib roast falling apart after 24 hours at 120˚—just below cathepsin's denaturing temperature of 122˚. But sous vide recipes never hold below 130˚ due to food safety fears (and with good cause—Douglas Baldwin shows 126.1˚ to be the highest point at which bacteria can multiply). At 130˚, cathepsins are gone.

The answer? Collagenases. Collagenases activate at 113˚F, peak at 130˚ and denature at 140˚. Baldwin claims collagen enzymatic degradation takes at least 6 hours, and I've found other references showing maximum benefit at 24-48 hours.

Maleficus_The_Terrible_1314869

Shouldn’t all the considerations for this, I.e. time, temp, ph etc, also include fat? Even as the collagens are doing their thing the fat pockets in the meat still need to render, whether it is a short rib or a strip, that takes time and doesn’t occur below 130 at a significant rate, Does it?