DouglasBaldwin

Hi Scotty, I have times and temperatures for venison in my cookbook. For leg, I recommend 1–2 days (24–48 hrs) at either 130˚F (55˚C) for medium-rare or 140˚F (60˚C) for medium. Personally, I'd start cooking it now at 130˚F (55˚C) and check how it feels about every 12 hours, then rapidly chill it when it feels right, and reheat it on Thursday. (The age and sex of the deer can make a huge difference and it's unlikely that you know either.) To check to see if it feels right, I just remove it from the water bath and gently squeeze it with my hand; I'd look for the same elastic feel you get from a chuck roast cooked for 24 hours at 130˚F (55˚C) — I want the meat to give when I squeeze it but still return to its original shape.

No, it's not quite that easy. First, egg yolk is about 26% fat, so 12% fat poultry meat probably isn't a good reference. Two, the cocktail of Salmonella species for those experiments may not have even include Salmonella enteritidis. I'll let the board know if I find something useful in the literature.

(1) Yes, I could probably determine a worst-case z-value and then compute a lower bound for pasteurization of intact eggs at 131˚F (55˚C). I don't have time to do that today, but I'll try to get to it soon and let you know. (2) From a pathogen destruction perspective, you can hold it for as long as you like at 131˚F (55˚C). I don't know if the proteins will eventually denature at that temperature and change the yolk's or white's texture. I used to think that yolk texture was only a function of temperature until Martin Lersch's Khymos blog post on April 23rd where he discusses a paper by César Vega and Ruben Mercadé-Prieto that shows that yolk texture is a function of both temperature and time. The lowest their graph goes is 140˚F (60˚C), so I don't know how long it'll take (if at all) for the yolk to change texture at 131˚F (55˚C).

If i remember correctly Modernist Cuisine calls for ~2 hours at 131 deg. for pasteurizing eggs. I did it with my circulator, but just to be on the safe side i used 132 (circulators and thermometers have measurement error..thought it would be good to be just a touch higher, and i don't know if they'll ever pasteurize below 131...i forget what the tables in MC list), which partially cooked the whites, they not look hazed. they're fine for cooking with, but not clear and perfect like the purchased pasteurized eggs. I talk about pasteurized in-shell eggs in my guide. I don't know how Nathan et al. got 2 hours at 131˚F (55˚C) since I haven't seen any z-values* for Salmonella enteritidis in intact eggs reported in the scientific literature. I recommend 1 hr 15 min at 135°F (57°C) based on experimental measurements at that temperature by Schuman et al. (1997). Note that the egg whites will be milky at this temperature and will take more effort to whip to the same volume. * The classical model for pasteurization gives a D- and a z-value for a particular pathogen in a particular medium -- in this case, Salmonella enteritidis in intact eggs: the D-value is measured at a specific temperature and tells how much time is required to reduce the pathogen by a factor ten; the z-value is measured in temperature and tells you how many degrees you need to increase (decrease) the temperature to decrease (increase) the D-value by a factor ten. Without known the z-value for Salmonella enteritidis in intact eggs, I don't know how to compute the pasteurization time for intact eggs at different temperatures. J. D. Schuman, B. W. Sheldon, J. M. Vandepopuliere, and H. R. Ball, Jr. Immersion heat treatments for inactivation of Salmonella enteritidis with intact eggs. Journal of Applied Microbiology, 83:438–444, 1997.

The step cooling method isn't unsafe and certainly makes sense in an industrial setting, where you're cooling a huge amount of food and the multistage step will save you quite a bit of electricity. Does it make a noticeable difference? I don't think it does. The experiments I did several years ago found a small but statistically insignificant difference in the amount of liquid lost during cooking. I'd of course be interested in hearing the results of any experiments that you might do.

Hi Kenneth, You didn't happen to measure the water temperature when you found it? The very long cooking will have inactivated all the vegetative (living) pathogens, so you'll only need to worry about the spores of Bacillus cereus and Clostridium spp. According to the FDA's Fish and Fishery Products Hazards and Controls Guidance (Table A-2), the maximum cumulative exposure times for these spore forming bacteria are: Salting would increase these times, but I can't tell you by how much since I don't have MC at the office to see what the salt and nitrite levels are. I hope this information will help you make a more informed decision. It sounds like you could be on either side of the maximum cumulative exposure time (especially when factoring in safety margins and the salt and nitrite levels).

Yesterday was a white, green, and greenish oolong day. All my brewing was in a 120 ml gaiwan with about 80 ml water. I started with Tea Source's Downy White tea (3.0 g at 160°F for 30 s, 30 s, 30 s); it was very pale yellow with a nice grassy taste and a hint toasty. Then I had some Xue Dian Mei Lan green tea from Norbu (5.0 g at 175°F 15 s, 10 s and 160°F 13 s, 15 s); it also had a fresh grassy taste with a pale yellow-green color; the first three steeps were quite nice but the fourth was too bitter for me. Finally, I enjoyed an extended session with Floating Leaves' Baozhong Farmer's Choice (Winter 2010) oolong; it had the light grassy taste of spring in the early infusions and a little more vegetal taste and increasing astringency in the later infusions (3.0 g at boil 15 s, 200°F 10 s, 10 s, 13 s, 190°F 13 s, 15 s, 15 s, 20 s, 20 s, 25 s, 25 s, 30 s, 30 s).

Thank you again for all your suggestions. So far, I'm really enjoying my foray into oolong teas. I ended up following Will's suggestions and ordered some tea from Floating Leaves (which arrived today) and from Tea Habitat (which arrived on Wednesday). I experimented with the Honey Orchid (commercial grade) from Tea Habitat yesterday and today. I used too much dry tea (5.0 g for my 120 ml gaiwan) on Thursday and I had trouble getting the times short enough and had to keep adding extra water. Today I tried again with 3.0 g (about 70 ml water; Boil: 15 s; 200°F: 10 s, 10 s, 13 s; 190°F: 13 s, 15 s, 15 s, 20 s, 25 s) and really enjoyed its sweet, mellow, peachy taste. I'm looking forward to trying some of the other (commercial grade) dan cong teas I got from Tea Habitat and the samples from Floating Leaves next week. I'm getting the distinct feeling that hanging out in this forum is going to be very bad for my bank account .

Thank you Will and Wholemeal Crank for your useful comments and suggestions. I gave another puer sample I'd ordered from Norbu a try yesterday (Lao Mansa, Sheng, Spring 2009); as suggested, I used more leaves (5.0 g) and much shorter infusion times (about 5 s each for the three rinses and then about 10 s for the infusion I tasted); it was mellower than my previous puer attempt but it was still to vegetal for me. While I do have a sample of Lao Cha Tou (Shu, Spring 2009), I think I'll hold off on trying puer teas for a few months -- stick to white and green teas and maybe adventure out into some oolong teas and then give puer teas another try. Do you have any oolong (or white or green) tea suggestions for a new to tea enthusiasts?

A few weeks ago I decided I wanted to start drinking tea at work. This was partly prompted by my officemate (a very nice Chinese post-doc) starting to brew tea in the office and partly in retaliation to the coffee culture of the rest of my department. My first step, of course, was getting everything I'd need to brew some nice white and green tea -- I'm still trying to learn to like pu-erh but I'm not there yet. So I ordered a travel Berkey (since Boulder, CO water tastes horrible) and so far I'm very happy with it. Then I ordered a Cuisinart CPK-17 kettle so I could easily heat my water to 160°F, 175°F, 190°F, and boiling and, so far, I'm very happy with it as well. Being of the scientific persuasion, I couldn't help but order a My Weigh Triton T2 300 g capacity scale with 0.1 g resolution (and calibration weight, of course). Then, I ordered two tea mugs with infuser baskets and some green and white tea from TeaSource -- where I'd ordered and enjoyed a bunch of tea from back in 2009. Finally, after reading a little more on this great forum, I ordered a pair of gaiwans, two green teas, and several pu-erh teas from Norbu. The last of it arrived on Monday and I've been brewing up a storm all week. First, I've been really enjoying the Man Tang Xiang (Spring 2010) and Xue Dian Mei Lan (Spring 2010) green teas I got from Norbu. For the first couple days I did 3.5 g in a 10 oz cup at 175°F for 2', 2.5', and 3'; this worked well for me. Then I tried Clouds & Mist Supreme green tea from TeaSource. I found it to be too astringent at 175°F (3.5 g; 10 oz water; 2') but it's much better at 160°F (3.5 g; 10 oz water; 2', 2.5', 3'). I don't like it quite as much as the above teas from Norbu but it's very drinkable. I've really enjoyed the free sample of High Mountain Supreme oolong that they included (3.5 g; 10 oz H20; 190°F; 2', 4', 6'), but I haven't had many oolongs so I can't say much other than I liked it. I like the Downy White white tea from TeaSource (5 g; 10 oz water; 160°F; 6',8',10') quite a lot and have been drinking it much more than the Clouds & Mist green tea. The next day I tried the 2007 Lincang Grade 1 Ripe pu-erh tea from Norbu (3.5 g; 10 oz water; Boil; 10", 3', 3.5', ...). I'd never tried a pu-erh before and it was a little too earthy for me. My officemate said he didn't like pu-erhs at first but has now grown to love them and was very curious about my impressions. I liked the fourth infusion more than the first three, but I don't think I'll give up my white and green teas just yet. Then, yesterday, I thought I'd try making some tea gongfu-style using my new gaiwans. Wow! I'm a complete convert. It's so much easier than I expected! Also, brewing in these little 120 ml gaiwans is so much more convenient than the 10 oz mugs -- no more cold tea at the bottom of my mug and no more infusers to clean! (I've got to thank Wholemeal Crank for mentioning using another gaiwan to drink from since it's so hard to find a teacup that isn't either way too small or way too large.) I can't say I taste a huge difference between the western and gongfu-styles, but I do like the greater control that comes with doing many small infusions. Yesterday I used 1.5 g of the Xue Dian Mei Lan green tea in about 70 ml of 175°F water and steeped for 5,3,4,4,5,6,... breaths (counting after filling and before pouring). Then I tried 2.5 g of tea and it was too strong and a bit astringent for me. Today I've done 2.0 g of both the Man Tang Xiang and Xue Dian Mei Lan green teas (70 ml water; 175°F; 5,4,6,8,...) and this worked well for me. Do these leaf-to-water ratios and times sound about right to you?

Hi Anna, I'll first address your question about the safety of cooking from frozen, then how it affects quality, and a brief comment on thawing. There is nothing inherently unsafe about cooking from frozen -- even conventionally -- so long as you measure the core temperature and verify that it's been pasteurized. In general, it takes about 50% longer to heat from frozen than it does from thawed. (Indeed, there was an active thread awhile ago on cooking frozen roasts in the oven.) So why does almost no one recommend cooking from frozen? Because very few cooks (outside of eGullet, of course) use a thermometer when cooking and so tend to under-cook frozen food. Also, many cooks are impatient, crank up the oven, and burn the outside before the core has even thawed -- I bet you've gone to at least one Thanksgiving dinner where the turkey was golden brown and frozen in the middle (I certainly have ). I think it's natural to cook from frozen sous vide because you don't have to worry about overcooking the surface while the core thaws and then comes up to temperature. The main problem with cooking from frozen sous vide is that it's very hard to accurately compute how long it'll take to heat the core to your desired temperature. That's why I've never posted pasteurization from frozen tables, because I'm just not satisfied with the agreement of my numerical calculations with my empirical measurements. I implemented several numerical algorithms but none of them met my expectations and it's far enough from my area of expertise (nonlinear wave phenomena) that I haven't had the time or inclination to revisit the calculations I did back in late 2008. (The only cook from frozen time in my cookbook is for a chicken breast in a 140°F/60°C water bath and I determined the 3 hour cooking time directly from a series of empirical measurements of chicken breasts that I froze a needle temperature probe in.) Now, there is a small difference in texture from cooking sous vide from frozen compared with cooking from thawed. This difference in texture isn't necessarily bad; indeed, sometimes I prefer the texture of cooked from frozen. My hypothesis is that this difference is caused by the proteins near the surface denaturing and being supported by the frozen core and then the denaturing of the core eventually being supported by the denatured proteins that surrounds it -- not unlike the slightly different texture of meat near a bone. But that's just a guess and the difference in texture is slight. So why is thawing in the fridge or in cold water recommended? Well, Nick hit it on the nose with concerns about the ``danger zone''. A lot of home cooks just plunk frozen food on the counter to thaw and the problem with this is that the surface may well reach room temperature before the core is thawed and so allow bacteria on the surface to multiply rapidly. Both thawing in the fridge or in exchanges of cold water greatly reduce the growth of surface pathogens. To get an idea of how quickly different pathogens multiply to dangerous levels at near refrigerator temperatures, check out Table A-2 (Time/Temperature Guidance for Controlling Pathogen Growth and Toxin Formation in Seafoods) in the FDA's Fish and Fisheries Products Hazards and Controls Guidance, 3rd Ed.

vengroff: You're quite right, numerically solving the heat equation is exactly what Nathan and I did. I'm very glad to see that you're using Robin rather than Dirichlet boundary conditions. In my home experiments I've measured that my PolyScience immersion circulator has a surface heat transfer coefficient of 155 W/m^2-K and my SousVide Supreme 95 W/m^2-K. You might want to include an option to set the water bath type and default to my measured surface heat transfer coefficients and also allow the user to set h. What shape are you assuming in your calculations? If possible, it'd be nice if the user could set a parameter based on the shape of the food that they're cooking. I'd think most people using your app will want to use it when cooking large items, like a roast, and being able to specify the shape is crucial for large items. The tables I use the most are those that give pasteurization times. You might want to consider adding a second line on your plot that also shows the log reduction of Salmonella, Listeria, E. coli, etc. You can find the equation and most the D- & z-values on my website. Please feel free to email me if you need any additional details. I wish you the best of luck on your app.

It's been awhile since I cooked sirloin but I seem to recall liking 6--8 hours at 130°F (55°C) for tri-tip steaks and sirloin tip steaks and 1--2 days for top sirloin steaks. If you've carefully calibrated your bath, you can drop the temperature down to 126°F (52.5°C) since Clostridium perfringens was shown not grow at that temperature (even when held at that temperature for three weeks).

So, it's true that we'd like everything to be rapidly chilled. The outgrowth of spores of C. perfringens isn't reserved to just sous vide cooking, since very little food that we cook is sterilized (as bmdaniel reiterated above). For customer leftovers and family leftovers, the portions are usually small enough that the refrigerator is able to cool them fast enough and people are told to use it or throw it out in a few days (so subsequent growth isn't a big problem). I harp about rapid chilling of sous vide cooked food because it's likely that you may want to hold it in your fridge for weeks (since it's safe at below 38°F to hold it for three to four weeks) and the pouch is frequently large enough (or you've cooked a large batch of items) that your fridge alone may not bring the temperature down fast enough to prevent outgrowth of spores. So if you've cooked a large item sous vide or a bunch of smaller items sous vide, I'd strongly suggest using an ice water bath. But if you have just a few chicken breasts leftover and you plan to use them in a day or two, you probably don't need to go to the effort of rapidly chilling them in an ice water bath and can just put them in your fridge (preferably on a wire shelf for increased airflow).

Sounds to me like you might need to calibrate your vacuum pressure gage. You can find instructions for doing that here.

Fair enough. I generated a new table tonight with core temperatures from 60°C to 67°C so you (and anyone else) can get the yolk consistency you want. EggHeatingTimes.pdf

Welcome to eGullet Dave! I'm the one who started the 2.75"-thick thing in my guide and it's overly cautious for two reasons: First, the 2.75"-thick restriction was assuming the slowest heat shape -- an infinite slab -- and a leg of lamb is somewhere between a cylinder and a sphere and so heats much faster and so can be thicker than 2.75". Second, when I wrote that section I conflated the importance of rapid cooling with rapid heating as well; the food safety literature seems to indicate that heating time isn't a critical control point (just rapid cooling) so long as the cooking time is sufficient to reduce the increase in pathogens caused by the slow heating (and 24 hrs at 130F is sufficient). [At some point, toxin formation and spoilage microorganisms may become a problem with extremely slow heating -- for instance, when rapid aging (see previous posts) for a day or more before increasing the temp to 130F or above -- but I haven't investigated this yet.]

coz: That's a good question, I don't know if `soft air release' would help; my intuition says it wouldn't help, but I don't have any way to test this hypothesis. Perhaps Nathan knows. I only mention chamber vacuum settings in my book under the chicken breast and fish recipes, where it's crucial. Since it doesn't hurt to use a 95% vacuum setting for everything, I usually leave my MVS 31 on that setting so I don't have to worry about forgetting and ruining some expensive fish*. * Being in Colorado, all good ocean fish is really expensive.

I also agree with Pedro that a chamber vacuum sealer is overkill in the home kitchen. Indeed, I've gotten a lot of emails from people who get worse results because they've used a chamber vacuum sealer: as Dave Arnold first pointed out to me, pulling a medium vacuum* can damage the texture of delicate foods and give them a mushy or pappy mouth-feel. That's not to say I don't use my chamber vacuum sealer for most my sous vide cooking, I just set my Minipack MVS 31 to pull a 95% vacuum. I very much prefer using Ziploc bags over a clamp-style vacuum sealers. If I didn't own my chamber vacuum sealer, I'd be perfectly happy using the heavy-duty Ziploc freezer bags I get at Costco for all my sous vide cooking. When using Ziploc bags, I just modify my recipes slightly by adding some (usually flavored) liquid to the bag so I can use my water-displacement method for getting most the air out. For instance, I usually use Ziploc bags when sealing up a Costco pack of boneless, skinless chicken breasts because it's faster than my chamber vacuum sealer; I put one breast and a 1/4 cup of chicken broth in a one-quart Ziploc bag and then use my water-displacement method to seal it up. * Chamber vacuum sealers pull "medium vacuums" and clamp-style vacuum sealers usually pull "low vacuums"; a "high vacuum" typically requires a two-stage vacuum process.

WhiteTruffleGirl: I also have a Minipack MVS 31 and love it. I got mine with a second 4mm seal instead of the cut-off; then if water or oil gets between the plastic and causes one seal to fail, I still have a second seal. Make sure you have a spot for it in mind: it's too heavy for one person to move easily and needs a lot of space above it to open the lid fully -- we ended up building a special shelf for it in our pantry.

The below is from an email I sent on 24 August, 2009. Edit: Note: I had to change the xls file to pdf since it won't let me upload an xls. Also, if you'd like me to compute tables for a lower than 64.5°C center temperature, just let me know and I'll post it. EggModelError.pdf Egg Cooking Times.pdf

I have a recipe for hard-cooked eggs in my cookbook: 167°F (75°C) for 45--60 min. As I posted in the old SV thread from my book: I did a lot of experiments to figure out the best mathematical model for cooking eggs so the white would be set firm and the yolk just starting to set; when I'm at my computer I'll generate a new table and post it here.

You're absolutely right that there many things that affect how tender cooked meat is. I certainly didn't mean to imply that the conversion of collagen into gelatin by thermal or enzymatic processes was the whole story: I was just trying to briefly clarify Pedro's post. I'd be very interested to know which recent articles you've found that illuminate this fascinating topic. You're certainly right that most the studies -- even recent ones -- use absurdly high temperatures and this limits their applicability to sous vide cooking. So everyone can follow the discussion, let's step back a moment and discuss the main ideas. Heat and Proteins Meat is roughly 75% water, 20% protein, and 5% fat and other substances. When we cook, we're using heat to change (or denature) these proteins. Which proteins and how much we denature them mainly depends on temperature and to a lesser extent on time. I like to divide the proteins into three groups: myofibrillar (50--55%), sarcoplasmic (30--34%), and connective tissue (10--15%). Myofibrillar proteins: While there are about 20 different myofibrillar proteins, 65--70% are myosin or actin. Myosin molecules form the thick filaments and actin the thin filaments of the muscle fibers. The muscle fibers start to shrink at 95--105°F (35--40°C) and the shrinkage increases almost linearly up to 175°F (80°C). The water-holding capacity of whole muscle meat is governed by the shrinking and swelling of myofibrils. Around 80% of the water in muscle meat is held within the myofibrils between the thick (myosin) and thin (actin) filaments. Between 105°F and 140°F (40°C and 60°C), the muscle fibers shrink transversely and widen the gap between fibers. Then, above 140°F--150°F (60°C--65°C) the muscle fibers shrink longitudinally and cause substantial water loss and the extent of this contraction increases with temperature. Sarcoplasmic proteins: Sarcoplasmic or soluble proteins are made up of about 50 components, but mostly enzymes and myoglobin. Unlike the myofibrillar proteins and connective tissue, sarcoplasmic proteins expand when heated. The aggregation and gelation of sarcoplasmic proteins begins around 105°F (40°C) and finishs around 140°F (60°C). As Nathan mentioned, before these enzymes are denatured they can significantly increase the tenderness of the meat. The ratio of myoglobin (Mb), oxymyoglobin (MbO2), and metmyoglobin (MMb+) also determines the color of the meat; see Belitz et al. (2004) pages 576--579 or Charley (1982) pages 395--398 for more details on meat color. Connective tissue: Connective tissue (or insoluble proteins) holds the muscle fibers, bones, and fat in place: it surrounds individual muscle fibers (endomysium) and bundles of these fibers (perimysium) and bundles of these bundles (epimysium). Connective tissue consists of collagen and elastin fibers embedded in an amorphous intercellular substances (mostly mucopolysaccharides). Collagen fibers are long chains of tropocollagen (which consist of three polypeptides wound about each other like a three-ply thread). Collagen fibers start shrinking around 140°F (60°C) but contract more intensely over 150°F (65°C). Shrinking mostly destroys this triple-stranded helix structure and is transformed into random coils that are soluble in water and are called gelatin. Elastin fibers, on the other hand, don't denature with heating and have rubber-like properties; luckily, there is much less elastin than collagen -- except in the muscles involved in pulling the legs backward. As Nathan reiterated, there isn't one temperature above which the collagen is denatured but that it increases exponentially with higher temperatures; for safety reasons, we usually use 130°F (55°C) as the lowest practical temperature for denaturing collagen. Tenderness: When chewing, you deform and fracture the meat. The mechanical forces include shear, compressive, and tensile forces; most studies use a Warner--Bratzler shear test perpendicular to the muscle fibers and this seems to correlate well with taste tests. Typically, W-B shear decreases from 120°F (50°C) to 150°F (65°C) and then increases up to 175°F (80°C). While this increase in tenderness used to be attributed to a weakening of connective tissue, most now believe it's caused by the change from a viscoelastic to an elastic material: raw meat is tougher because of the viscous flow in the fluid-filled channels between the fibers and fiber bundles; heating up to 150°F (65°C) increases tenderness because the sarcoplasmic proteins aggregate and gel and makes it easier to fracture the meat with your teeth; over 150°F (65°C) and up to 175°F (80°C), the meat is tougher because the elastic modulus increases and requires larger tensile stress to extend fractures (Tornberg, 2005). Both the intramuscular connective tissue and the myofibrillar component contribute to toughness. In many cuts, connective tissue is the major source of toughness, but the myofibrillar component is sometimes dominant and referred to as actomyosin toughness. Connective tissue toughness: Both the collagen content and its solubility are important. Muscles that are well worked have connective tissue that makes them tougher than muscles that were exercised comparatively little or that are from young animals. The more soluble the collagen, the more tender the meat is and collagen from younger animals tend to be more soluble and soluble at lower temperatures. Actomyosin toughness: Actomyosin toughness can be a major contributer to toughness in young animals and in relatively little used muscles. Immediately after slaugher, the warm flesh is soft and pliable. In a few hours, the meat goes into rigor and becomes rigid and inelastic. Cross-links form between the myosin and actin filaments where they overlap -- where the muscles are allowed to contract or shorten -- and are locked in place during rigor. After rigor has passed, the meat again becomes soft and elastic. (If pre-rigor meat is chilled to below 60°F (15°C), then cold-shortening of the muscles may occur and significantly increase toughness.) Enzymes Recall that enzymes make up a significant portion of the sarcoplasmic proteins. The sarcoplasmic calpains and lysosomal cathepsins enzymes are especially important in aging (which is also called conditioning). These enzymes catalyze the hydrolysis of one or more of the proteins -- calpains the Z line proteins and cathepsin the myosin, actin, troponin, and collagen proteins. Dry aging is usually done at 34--38°F (1--3.3°C) with about 70% humidity for 14 to 45 days. Higher temperature aging is also possible, see Lawrie (1998) page 239--40 or some of mine, Pedro, and Nathan's posts in the previous thread. As Nathan just discussed, this higher temperature aging at 113°F (45°C) for even 4 hours can significantly improve tenderness. (Lawrie notes that at 120°F (49°C) that tenderness is particularly increased but that it has a somewhat undesirable flavor.) At our sous vide cooking temperatures between 130 and 140°F (55 and 60°C), many of the enzymes have been denatured but some of the collagenases are active and can significantly increase tenderness. References H.-D. Belitz, W. Grosch, and P. Schieberle. Food Chemistry. Springer, 3rd edition, 2004. Helen Charley. Food Science. John Wiley and Sons, second edition, 1982. R. A. Lawrie. Lawrie’s Meat Science. CRC, 6th edition, 1998. E. Tornberg. Effect of heat on meat proteins—implications on structure and quality of meat products. Meat Science, 70:493–-508, 2005.

Douglas, do you know the optimal temperature (e.g. for fastest breakdown) for that enzyme to operate at? I'm sorry, but I don't. The articles that I've read just say it's active over 50--60°C (120--140°F). Part of the problem is that there are many different collagenases from different sources and with different properties (Belitz et al., 2004). The original article, Laakkonen et al. (1970), heated beef at 0.1°C/min until it reached 60°C (140°F) and held it there for a total of 12 hours and measured various properties every hour. They found very little change over the first 4 hours, when it was below 50°C (122°F); then significant tenderizing over the next two hours, when it was between 50 and 60°C (122 and 140°F); and then a slower increase in tenderness up until they stopped the experiment at 12 hours. Note that one of the three muscles they tested, longissimus, didn't show further tenderizing after the sixth hour. E. Laakkonen, G. H. Wellington, and J. W. Sherbon. Low-temperature, long-time heating of bovine muslce. J. Food Sci. 35 (1970) 175--183.

Pedro is quite right about collagen being convert to gelatin by two processes: enzymatic and thermal. The sarcoplasmic protein enzyme collagenase remains active below 140°F (60°C) and can significantly tenderize the meat if held for more than 6 hours (Tornberg, 2005). However, the thermal breakdown of the collagen into gelatin is also important at these temperatures, especially when the cooking time is in the 12--72 hour range. The thermal breakdown of collagen into gelatin goes much faster at higher temperatures -- almost all tenderizing occurs within 12--24 hours at 175°F (80°C) (Davey et al., 1976) -- and it takes roughly twice as long for every 10°C (18°F) that you decrease the temperature. Almost all the water lose caused by shrinking muscle fibers occurs by 175°F (80°C) and there is very little change in the color or texture of the meat above this temperature. Indeed, this is why you can get similar pulled-pork from 60 min in a pressure cooker and from 8--10 hours at 175°F (80°C). As Pedro mentioned, vegetables are a different story: non-starchy vegetables need temperatures of around 180--185°F (82--85°C) to dissolve the cementing material (pectic substances) that holds their cells together; starchy vegetables, like potatoes, can be cooked at the lower temperature of 175°F (80°C) because of the gelatinization of their starches.