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I was watching S13E16 of Good Eats and to cook his chicken for "chicken and dumplings", he places an old hen (instead of a rooster) in the pressure cooker at the maximum temperature & pressure. I've done a bit of searching and it seems pressure cookers are recommended for stocks since it can denature collagen in the connective tissues in tough meats and other pieces to gelatin faster.

This makes sense, except I thought the whole point of slow roasting (and indeed sous-vide) is to use low temperatures over a long period of time for collagen to gelatin conversion.

Why is the low temperature needed in this, and the high temperature needed for the pressure cooker? It seems a bit contradictory. If the higher temp and pressure is better, we should be able to sous-vide in a pressure cooker too.

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Sous-vide and slow-roasting (or braising) have different purposes. Slow roasting still gets things pretty hot (generally at least to 100C), and tenderizes tough meat. Sous-vide cooks things barely at the temperature they require to be fully-cooked, which makes it really good for tender meats that you don't want to overcook. –  Jefromi Oct 20 '12 at 19:48
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@Jefromi You can cook tough cuts of meat sous vide (I do it all the time) you just have to cook it for a long time, how long depends on what temperature and the result you want, e.g., you might do a pork belly at 70C for 18 hours (making the meat flaky like a braise) or beef short ribs at 55C for 72hrs (the meat medium rare like a steak but tender as the filet mignon). –  Stefano Oct 23 '12 at 11:23
    
@Stefano I know you can do it, but I think everything I said is still true. You wouldn't braise a filet mignon, and you're not missing out too much if you braise a pork shoulder. –  Jefromi Oct 23 '12 at 13:18
    
@Jefromi, I am pretty sure that the basic chemistry of roasting and sous-vide is the same: trying to convert as much collagen to gelatin before the outside of the meat gets too cooked and dry. Of course, with sous-vide being a newer technology, one has create control of the temperature and with the air tight bag and reduce losses of moisture. This question is very focussed on chemistry. Trying to throw out all intuition and traditions. –  Kent Oct 23 '12 at 17:41
    
Again, the point that I'm making here is that both work fine for tough things where you want to convert collagen (though sous-vide takes some effort, and people who don't have a setup will be just fine without it), but one of the main points of sous-vide is cooking things that you don't want to get that hot, like for example a steak that you want to cook to 50C, not 100C. Sous-vide can cook at lower temperatures, and slow-roasting (in a normal oven) and braising can't. They're not the same technique, even though they both can work on tough meat. –  Jefromi Oct 23 '12 at 17:45

2 Answers 2

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What you need for the conversion of collagen is a certain amount of energy. It is a complicated process - the melting point is around 70°C for the type of collagen contained in beef, but the melting does not happen instantly once the meat reaches 70°C. In a pressure cooking, you can apply the same amount of energy in a shorter amount of time. This is not bad, as opposed to slow roasting of collagen-poor meat.

In collagen-poor meat, you have two types of protein, which are soft and wet. Under heat, they curdle, becoming tough and dry. The perfect meat is when the first type has curdled (so the meat is not raw) but the second hasn't, so it still holds juices inside. If you curdle both, your meat gets tough and you can't take it apart with your teeth.

In collagen-rich meat, you curdle both proteins - the collagen itself is tough and you want to melt it, but this happens long after the meat has curdled. But because the muscle fibers are not clinging to each other, but separated by collagen, you still get tasty meat. For that, you melt the collagen into gelatin, and serve the meat warm, so that the dry fibers are separated by the smooth, juicy melted gelatin. Unlike slow-roasted meat, you don't have to tear the juiceless fibers apart, and the gelatin makes up for the missing meat juices which were expelled from the cells during curdling.

So, in slow-roasted meat you don't want to cross the temperature limit for curdling a certain protein, this is why you have to apply heat slowly until the center of the meat has cooked, without the outside getting overcooked. In collagen-rich meat, there is no upper limit at which the meat gets non-tasty, so you can push the energy needed for the collagen-to-gelatin conversion quickly into your meat. The pressure cooker can do this better than the normal boiling process.

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Thanks for the great reply. I would love to learn more about these two types of proteins. Collagen in connective tissues is one type. What's the other? It just sprung up in the answer without an explanation. Also, I should clarify with physics what is meant by "pushing the energy". Energy transfer via conduction, which is the case here, is determined by the temperature difference and contact surface area. I guess this is why pressure cooking is good for this purpose: it offers the large contact surface of being submerged in liquid, while the higher temperatures close to slow roasting. –  Kent Oct 23 '12 at 17:42
    
No, the proteins making up the muscle fibers are called actin and myosin. Collagen is also a proteins, but it is a connective tissue, not intended for movement, and has a different structure. I don't know a good web source to learn about them, read Potter's "cooking for geeks" or McGee's "On food and cooking" about details. The first is the easier read, the second is much more complete. And the comparison between roasting and pressure cooking is more difficult, because you have both radiation and conduction in roasting. Also, surface stays the same, but the coefficient of air is different. –  rumtscho Oct 23 '12 at 18:04

This is something I feel confuses a lot of people when talking about sous-vide cooking. I think the best way to think about sous-vide is as "low temperature cooking". In these temperature ranges collagen breakdown can still occur but it takes significantly more time than it would at higher temps in a traditional braise or in the pressure cooker where, depending on your elevation, water can boil at 121C.

The real answer depends on what your goal is. If you want the texture of a traditional braise you could cook something at say 85C for 8-10h and it would be fall apart tender just like in a pot in the oven or the pressure cooker. Now if that was your goal I would say save the time and do it another way. However, if your goal is to augment the texture of a food through SV cooking then cooking for a significantly longer period of time at a lower temperature will give you textures you cannot achieve any other way. So a short rib cooked at the 85C/8-10h will be falling apart like mom's old school pot roast but if you went lower at say 54C/72h it would be as tender as a tenderloin cut but with an intense meaty flavor and beautiful medium rare color.

So for a recipe like Alton Brown's chicken and dumplings he wants to accomplish this conversion as quickly and efficiently as possible and is likely using the collagen rich chicken stock created from the process in the soup so that's why I would turn to the pressure cooker. Plus, he's a TV chef so he's not going to be recommending non-mainstream cooking procedures like sous-vide at that point in time.

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