100 replies to this topic

[scott123]

Nobody *makes* espagnole a la Escoffier anymore so I think it is safe to retire the old definition of demi-glace in favour of the more common, modern usage.

Demi-glace = stock reduced to sauce consistency
Glace = stock reduced to more than sauce consistancy.

I am in complete agreement.

[deltadoc]

Nobody *makes* espagnole a la Escoffier anymore so I think it is safe to retire the old definition of demi-glace in favour of the more common, modern usage.

Demi-glace = stock reduced to sauce consistency
Glace = stock reduced to more than sauce consistancy.

I am in complete agreement.

I guess that makes me a "nobody", because I take great relish in making Fonds de Veau Brun ala Escoffier Recipe #9 (from organic veal bones from New Zealand). I then make the Sauce Brun ou Sauce Espagnole ala Escoffier Recipe #22 . Then I make the Demi-glace ala Escoffier Recipe #23. (Note: different editions of Escoffier's Cookbook and guide to the fine art of cookery show different types of wine to add to the demi-glace: my edition states "an excellent Sherry").

I have also made Glace de Veau Viande ala Escoffier Recipe #15 from leftover veal stock (Recipe #9) rather than reducing Fonds Brun ou Estoufade (Recipe #7) when I didn't have enough canning jars left to can the remaining fresh stock. The stock in the canning jars always tastes as good as the day I made it even 2 years later.

I have however not been as thrilled with the Glace de Veau Viande, as it does lose some brightness from the prolonged reducing period. When I do use it, I never reconstitute it, but add a tsp or TBSP or two to another sauce as an added layer or fortification of flavor.

Interestingly enough Escoffier discusses that "many chefs of the old school do not permit the use of glaces in culinary preparations". I wonder how "old" the "old school" is that he refers to, as it would appear that chefs today refer to Escoffier's methods as "old school"??

doc

[paulraphael]

Nobody *makes* espagnole a la Escoffier anymore so I think it is safe to retire the old definition of demi-glace in favour of the more common, modern usage.

That makes me nobody too.

I'd agree that hardly anybody makes the stock for their demis a la escoffier anymore--i wonder if even trois etoille french restaurants have the budget to use 16 pounds of meat and bones to produce a quart of demi. but that's really not my point.

What I've been finding is that a lot of people make glace de viande and call it demiglace. This is just confusing because it destroys a significant distinction.

The working definitions you give (demi = stock reduced to sauce consistency, etc.) are ok, because they preserve the distinction. They won't lead someone with a half-baked education to make a cup and-a-half of brown sauce with a whole cup of glace de viande.

Edited by paulraphael, 01 January 2007 - 04:45 PM.

[paulraphael]

Interestingly enough Escoffier discusses that "many chefs of the old school do not permit the use of glaces in culinary preparations".  I wonder how "old" the "old school" is that he refers to, as it would appear that chefs today refer to Escoffier's methods as "old school"??

doc

This is a great observation. I suspect Old School to Escoffier was the 17th and 18th century, when the chefs were in service to the kings and aristocracy, and didn't have to deal with the vulgarities of a la carte cooking, restaurants, the middle class, and budgets. Back then, naturally thickened jus (called coulis) were prepared as sauces for roasts and sautees. This was done a number of ways, but it all amounted to cooking a lot of pieces of meat in order to get enough sauce for one piece.

In a sense this is what we do with stocks, but we use bones and much cheaper cuts, and long cooking and reduction in order to concentrate flavors. This is just not capable of achieving the fresh complexity of a natural jus or coulis.

The simplest approach was to roast multiple pieces of meat on spits, and eventually collect enough jus to serve with the final roast.

Sometimes they would squeeze all the juice out of these pieces of meat in a big iron press.

Another approach was to make stock from the poaching or braising liquid from a piece of meat, and then to poach another piece of meat in that liquid. This was called a double coulis. A tripple coulis might also be prepared. I don't know what all these extra pieces of meat were used for. Given to the dogs, maybe, or the kitchen staff.

At any rate, after the revolution disenfranchised the chefs from their patrons (and their patrons from their heads) the middle class was born, along with restaurants and a la carte cooking. The old ways wouldn't work with the new time and budget constraints, so chefs created time and money-saving shortcuts to simulate the favor of the grand old coulis.

Careme and the chefs of his generation created these shortcuts (including the family tree of classic sauces and glaces). It's worth remembering that the extravagant preparations of haute cuisine (like double stocks made with staggering amounts of meat) were actually born as shortcuts.

Escoffier's methods from a generation later no doubt simplified and economized Careme's shortcuts, just as the mid-20th century chefs simplified and economized Escoffier's, and the chefs of Nouvell cuisine simplified and economized theirs, and as our generation is currently simplifying and economizing theirs.

This isn't to say that a restaurant that makes a demiglace by reducing stock made from bones and vegetable ends is doing anything wrong, but it's folly if they don't recognize their methods as a shortcut on a shortcut on a shortcut, many times over.

[Reefpimp]

Hong Kong Dave hit the nail on the head with his comment about the increased surface area of frozen demi-glas cubes.

The other thing I do for stock/glace preservation is to make sure I add salt. I used to make all my stocks/glaces salt free and then add salt to the final dish, but their shelf life was cut way too short. So I add salt. Salt is a big player in this equation. If you can work with an extremely salty demi or glace (I can't) freezing may not even be necessary. Heck, refrigeration may not even be necessary.

This brings us right back around to the original precursor to bullion cubes, ca. 1800: "portable soup," which readers of the Aubrey/Maturin books by Patrick O'Brian will recognize. One would take demi down to au sec, then let it cool into sheets, to be reconstituted as needed. I haven't tried this but I think it's a dandy idea. I've taken to reducing all my own stocks by 90%, plus or minus, and I go through them fast enough that shelf life really isn't an issue.

However comma space: The restaurant at which I work has recently taken to ordering whole ducks (We confit four dozen legs at a time) instead of just the skin-on breasts, which (although it means I spend a morning a week in a pretty high state of grease, is great. We end up with a surplus of bones, so I am fairly soon going to have to make a great big batch of stock for myself (Chef, while testy, is cool like that. I just wish he'd ease up and let me use the RoboCoupe instead of the mortar for making Caesar dressing). SO I'm gonna try a 'spearamint: I'm going to take one batch of duck demi and salt it fairly aggressively. I'm going to take another batch and add a generous portion of Everclear to it off-heat, let it sit for half an hour, then re-heat and flame it, to drive off the alcohol. Both will be placed in 1-cup Tupperware containers straight out of the dishwasher and left to sit out on my kitchen counter until one or the other starts to grow things. We shall see if either or both helps.

[scott123]

SO I'm gonna try a 'spearamint:  I'm going to take one batch of duck demi and salt it fairly aggressively.  I'm going to take another batch and add a generous portion of Everclear to it off-heat, let it sit for half an hour, then re-heat and flame it, to drive off the alcohol.  Both will be placed in 1-cup Tupperware containers straight out of the dishwasher and left to sit out on my kitchen counter until one or the other starts to grow things.  We shall see if either or both helps.

Don't forget a control- a third demi with neither everclear nor salt.

And must you use duck demi? A chicken demi would reveal the same keeping capabilities without sacrificing your precious duck stock.

[demiglace]

Nobody *makes* espagnole a la Escoffier anymore so I think it is safe to retire the old definition of demi-glace in favour of the more common, modern usage.

Demi-glace = stock reduced to sauce consistency
Glace = stock reduced to more than sauce consistancy.

You haven't lived if you haven't tasted the *real* thing.

[scott123]

Nobody *makes* espagnole a la Escoffier anymore so I think it is safe to retire the old definition of demi-glace in favour of the more common, modern usage.

Demi-glace = stock reduced to sauce consistency
Glace = stock reduced to more than sauce consistancy.

You haven't lived if you haven't tasted the *real* thing.

I'm not a big fan of the dark irony note that browned/long cooked tomatoes get nor do I enjoy the alcoholic bite of uncooked sherry (or madeira, port, etc.).

[paulraphael]

Nobody *makes* espagnole a la Escoffier anymore so I think it is safe to retire the old definition of demi-glace in favour of the more common, modern usage.

Demi-glace = stock reduced to sauce consistency
Glace = stock reduced to more than sauce consistancy.

You haven't lived if you haven't tasted the *real* thing.

I'm not a big fan of the dark irony note that browned/long cooked tomatoes get nor do I enjoy the alcoholic bite of uncooked sherry (or madeira, port, etc.).

Me neither. At least not enough to make it a standard part of the preparation. I do what I think a lot of people do ... make a less authentic but more versatile version by leaving out the tomatoes and the fortified wine.

[paulraphael]

So has anyone sucessfully stored demi ice cubes by individually wrapping in plastic and then putting a few together in small ziplock bags?

[Ruth]

So has anyone sucessfully stored demi ice cubes by individually wrapping in plastic and then putting a few together in small ziplock bags?

I generally store my demi (about two cups at a time) directly in small ziplocs but I also fill one ice cube tray and wrap the cubes individually in plastic once they are frozen. I follow exactly the same procedure with egg whites and even heavy cream and crème fraîche which are even more prone to pick up off-flavors. I have never had a problem and those little cubes are a wonderful resource to have available.

[Reefpimp]

Don't forget a control- a third demi with neither everclear nor salt.

And must you use duck demi? A chicken demi would reveal the same keeping capabilities without sacrificing your precious duck stock.

Sorry, I thought I'd included that but I see I didn't.

I have to pay for chicken (we don't serve it at the restaurant), so none's around. I get duck bones for free.

[Shalmanese]

Me neither. At least not enough to make it a standard part of the preparation. I do what I think a lot of people do ... make a less authentic but more versatile version by leaving out the tomatoes and the fortified wine.

Without the tomatos and the wine, isn't it just a roux thickened brown stock?

[paulraphael]

Without the tomatos and the wine, isn't it just a roux thickened brown stock?

Maybe, but I've seen sources noting these as normal variations on espagnole (if used for demiglace) going back a long time.

You can always add reduced tomatos or spirits to a sauce if you want them; removing them is another story.

I think the larger issues involve the quality of the stock used, and the degree of reduction.

Edited by paulraphael, 02 January 2007 - 03:25 PM.

[HKDave]

HKDave: 2 cups of Demi is 20 cups of stock. I have no idea how you can use that much demi so fast or how you find the time to make that much in the first place. 2 cups of demi would last me 3 months.

I have a big stockpot. It takes almost the same amount of my time to make a big or small batch; a big batch just has to sit on the stove longer to reduce which doesn't require additional effort on my part. Two cups lasts me a long time, too; that's the whole point. I'm not going to make demi every couple of weeks.

Re the other poster's comment that re-boiling to extend the fridge life of stock/demi is a myth, well, it works in the real world.

[scott123]

Is that who I am? The 'other poster?' Well, since quoting etiquette seems to have gone out the door, tell 'that guy' who said re-boiling stock 'works in the real world' that 'working' is subjective. Sure he survived boiled stock and maybe it didn't taste terribly off, but the bacteria were there- in very 'real' way.

Why take unecessary chances with food? Freeze it.

P.S. If you work in a kitchen, don't get caught by the health inspector doing that 're-boiling' bullshit.

Edited by scott123, 04 January 2007 - 12:51 AM.

[paulraphael]

P.S. If you work in a kitchen, don't get caught by the health inspector doing that 're-boiling' bullshit.

Could you elaborate? How does ten minutes of simmering not kill bacteria?

I know it's traditional in French kitchens to keep stock pots going for days at a time, getting depleted and replenished (but not completely changed). And it's also pretty normal procedure for certain soups and stews (like a pot au feau) to be kept going almost perpetually through refrigerating, replenishing, and simmering.

I haven't seen any science related to this; if you know of any I'd love to check it out.

[scott123]

P.S. If you work in a kitchen, don't get caught by the health inspector doing that 're-boiling' bullshit.

Could you elaborate? How does ten minutes of simmering not kill bacteria?

I know it's traditional in French kitchens to keep stock pots going for days at a time, getting depleted and replenished (but not completely changed). And it's also pretty normal procedure for certain soups and stews (like a pot au feau) to be kept going almost perpetually through refrigerating, replenishing, and simmering.

I haven't seen any science related to this; if you know of any I'd love to check it out.

From Bone Appetit by Robert L. Wolke

…according to my correspondents, among them a food safety consultant and a biochemist at the National Institutes of Health. It seems that all bacteria are not necessarily killed at 212 degrees Fahrenheit. Some of them can survive by forming highly invulnerable spores.

…A common pathogenic -- disease-causing -- genus of spore-forming bacteria found in soil, water and the intestinal tracts of humans and animals is Clostridium, especially the species C. perfringens, which is a major cause of food poisoning, and the much rarer C. botulinum, which produces botulin toxin, one of the most potent poisons known. Clostridium bacteria don't need oxygen to live; in fact they can't survive in air, so the interior of a pot of stock is a perfect growth medium.

To kill these spores, temperatures higher than 212 degrees are needed. That's why medical and surgical equipment is sterilized in an autoclave, a sort of pressure cooker.

Quoting guidelines prevent me from posting more of the article- I highly recommend reading the whole thing as it goes into far more detail regarding the ways in which these bacterial spores can survive boiling temps.

[Reefpimp]

Correct me if I'm wrong, gentlemen, but the presence of those spores in the stock is contingent on the bacteria being there in the first place. Which-- given that the bones are roasted at 400, the vegetables are caramelized at 350 or so, and the water is chlorinated, UV-treated, and boiled--shouldn't be the case.

This is why I love Classical cooking: If you do it right; if you perform each (in itself) very simple step right, you almost can't go wrong. Also, I would like to point out that commercial, feedlot beef and henhouse chickens are much more loaded with (for lack of a better term) impurities. I've been getting grass-fed bison and mixed-breed beef bones for my beef stock. It's cool, everything behaves exactly as Auggie E says it should; no need to correct or tweak at all. I buy free-range chickens from an Amish family 30 miles from here, and until the restaurant started getting in whole ducks, I sourced my duck bones from the sky. No overcrowding issues there I believe. I hope Wisconsin can get the Chronic Wasting Disease thing under control soon, because I miss my venison glace.

[scott123]

Correct me if I'm wrong, gentlemen, but the presence of those spores in the stock is contingent on the bacteria being there in the first place.  Which-- given that the bones are roasted at 400, the vegetables are caramelized at 350 or so, and the water is chlorinated, UV-treated, and boiled--shouldn't be the case.

Reefpimp, the bacterial spore threat relates only to the myth that re-boiling stock every few days will maintain it's freshness/edibility. The initial process isn't in question. It's the post-cooled stock we're talking about. During cooling, micro-organisms from the air take root. This is where the threat stems from. Re-boiling it every few days does nothing to remove that threat.

[HKDave]

Is that who I am? The 'other poster?' Well, since quoting etiquette seems to have gone out the door, tell 'that guy' who said re-boiling stock 'works in the real world' that 'working' is subjective.  Sure he survived boiled stock and maybe it didn't taste terribly off, but the bacteria were there- in very 'real' way.

Scott, my apologies if you were offended; the reason I didn't quote you by name is that your quote was on a previous page when I was posting, and I couldn't figure out how to scroll back to see your name (and I don't know how to do the multiple quotes thing). No rudeness intended; you're reading a negative tone into my post that I assure you isn't there.

Regarding the quote from Bone Appetit (which I will read, thanks for the recommendation), every C. perfringens outbreak I've read about was related to improper cooling/holding, usually of big roasts, rather than prolonged storage of liquids at fridge temperatures followed by full re-heating. Here's the most similar case I could find, this from the US FDA's 'Bad Bug Book':

"In November, 1985, a large outbreak of C. perfringens gastroenteritis occurred among factory workers in Connecticut. Forty-four percent of the 1,362 employees were affected. Four main-course foods served at an employee banquet were associated with illness, but gravy was implicated by stratified analysis. The gravy had been prepared 12-24 hours before serving, had been improperly cooled, and was reheated shortly before serving. The longer the reheating period, the less likely the gravy was to cause illness." (italics mine)

This shows that properly reheating liquid does kill this bacteria, even in an extreme situation where the product wasn't cooled fast enough and the bacteria multiplied to dangerous levels - something that's not the case in my kitchen. Labensky's 'On Cooking' textbook also says C. p. can be prevented by re-heating to 74c or higher. So while I don't wish to dispute Wolke on C.p. possibly being able to survive boiling, from a practical as well as historical standpoint, re-boiling does seem to work.

[scott123]

Is that who I am? The 'other poster?' Well, since quoting etiquette seems to have gone out the door, tell 'that guy' who said re-boiling stock 'works in the real world' that 'working' is subjective.  Sure he survived boiled stock and maybe it didn't taste terribly off, but the bacteria were there- in very 'real' way.

Scott, my apologies if you were offended; the reason I didn't quote you by name is that your quote was on a previous page when I was posting, and I couldn't figure out how to scroll back to see your name (and I don't know how to do the multiple quotes thing). No rudeness intended; you're reading a negative tone into my post that I assure you isn't there.

Regarding the quote from Bone Appetit (which I will read, thanks for the recommendation), every C. perfringens outbreak I've read about was related to improper cooling/holding, usually of big roasts, rather than prolonged storage of liquids at fridge temperatures followed by full re-heating. Here's the most similar case I could find, this from the US FDA's 'Bad Bug Book':

"In November, 1985, a large outbreak of C. perfringens gastroenteritis occurred among factory workers in Connecticut. Forty-four percent of the 1,362 employees were affected. Four main-course foods served at an employee banquet were associated with illness, but gravy was implicated by stratified analysis. The gravy had been prepared 12-24 hours before serving, had been improperly cooled, and was reheated shortly before serving. The longer the reheating period, the less likely the gravy was to cause illness." (italics mine)

This shows that properly reheating liquid does kill this bacteria, even in an extreme situation where the product wasn't cooled fast enough and the bacteria multiplied to dangerous levels - something that's not the case in my kitchen. Labensky's 'On Cooking' textbook also says C. p. can be prevented by re-heating to 74c or higher. So while I don't wish to dispute Wolke on C.p. possibly being able to survive boiling, from a practical as well as historical standpoint, re-boiling does seem to work.

Dave, I did read a dismissive tone into your post, and I also flew off the handle (just a little bit ), which I apologize for doing. I can now see that you weren't being dismissive at all.

I think it's important to convey the fact that I don't see the perpetuation of the re-boiling myth as a public health crisis. I don't think x number of people are dying every year because of consuming re-boiled stock. Or even x number people are getting sick. Re-boiling probably does kill off quite a few bacteria, and, although many people subscribe to the re-boiling paradigm, I get the feeling that very few people actually re-boil stock, and, those that do probably don't re-boil it more than a couple of times.

The chance of getting sick from re-boiled stock is probably extremely low. My guess is that it's far less than getting sick from a raw egg and that's 1 in 10,000 (if you live in the NE US and even less elsewhere). It could very well be in the realm of 1 in 100,000 or even 1 in a million.

My point is 'why take the chance?' Do you really want to be that millionth person? Would you want your loved ones to be? Your restaurant patrons? If you freeze the stock, the threat is removed.

For me, the autoclave example is especially compelling. If boiling kills all the nasties, why do hospitals use autoclaves?

If re-boiling was portrayed as a last resort, I think I'd be okay with it (I found some stock in the back of my fridge that's 10 days old, what do I do?). My problem is the perpetuation of the idea that stock can be re-boiled indefinitely. Months, years, decades. That concerns me- the portrayal of this repercussionless utopia where stocks live longer than we do

[Reefpimp]

Well, thanks for taking the time to at least think about what i said. And consider this in re the re=boiling: Botulism is anaerobic, and C. Perfringens is a micro-oxyphiliac (I think that's the right term). So by the very act of boiling, even very gently, it aerates the stock quite thoroughly, and thus providing a hostile environment.

No, stocks won't survive forever. But for safely storing glace for a few months, I think we're all gonna be okay if we follow HAACP guidelines and exercise a little common sense. Besides, it's healthy to expose your body to toxins every so often, right? Isn't that what Friday nights after close are for??

Edited by Reefpimp, 05 January 2007 - 08:38 PM.

[coquus]

Let me tell you guys what I think about storing demi-glace for home use. Don't bother, find a restaurant that makes their own, make friends with the chef, and barter, barter, barter. It's generally not worth buying what is sold as demi-glace, and making your own is worthless, because you throw away too much to spoilage. I make my own because I like cooking, some would call me crazy. I don't keep demi-glace however, reduce it by half and store it as glace de viande in small cubes in my fridge in glass jars, ten pounds of beef(chicken, pork, other game or fowl bones also acceptable) keeps me for six or eight months that way. I guess it's not right to call it glace de viande(a la Jacques) as it is not the result of a second boil but simply an extended first boil. Really, it is just demi glace reduced over medium heat for a while, then over low until there isn't any water. When it gets moldy, you didn't do it right, re melt, and further reduce, and throw it away if there is any other mold besides white mold on it. There is a noticable a taste difference to demi glace, but in no way is it bad, and it should not taste burnt (you also screwed up). It's good for some recipes, not for others, if any other way is better, school me egullet. Does anybody who lives by the ocean do this with fish, if so what kind?

Edited by coquus, 09 January 2007 - 09:52 AM.

[zoe b]

I was just reading the Les Halles Cookbook while I was eating lunch and saw that AB said that a lot of chefs don't even bother with the veal demi-glace now--just do a dark chicken one--any thoughts on this?

I'm going to make a D-G in the next few weeks--have to collect the bones--which is more versatile in your opinion? Obviously the chicken one won't have quite as much of the gelatinousness of the veal base--any other differences?


Z

[paul o' vendange]

I do both. I don't actually roast my veal bones - following on Thomas Keller's method, I find the non-roasted demi lends a more subtly sweet, round and versatile quality to many other sauces. My dark chicken "demi," made with roasted bones, meat trim, and vegetables, is just as gelatinous, just as useful, but has more of a roast quality, for obvious reasons. When I want a more pronounced or sharper character of this sort, I will go with the dark chicken.

[UnConundrum]

Wasn't it discussed in the thread on storing demi that much of the gelatin in stock is broken down in making demi? I know not all, as the demi itself is quite thick, but I got the impression that demi is not a substantial source of gelatin. Is this wrong?

[paul o' vendange]

Wasn't it discussed in the thread on storing demi that much of the gelatin in stock is broken down in making demi?  I know not all, as the demi itself is quite thick, but I got the impression that demi is not a substantial source of gelatin.  Is this wrong?

I read the thread, but I'm afraid I can't agree. Gelatin is a breakdown product of collagen, but from what I know, gelatin itself is not heat labile; it survives heating quite nicely. If it didn't, glace would not be as thick as it is...

Looking through McGee on the subject:

Gelatin owes its remarkable properties to a peculiar amino acid makeup...which gives it a great affinity for water molecules, prevents its chains from coiling into more compact helical structures, and prevents the chains from coagulating when heated.  Some sauces, especially the concentrated, starchless reductions favored in the "nouvelle cuisine," owe their texture entirely to their gelatin content.

- i.e., classic espagnole based sauces would be aided by starch, and the imperfect proteins found in flour. But today's reduced stocks are almost entirely thickened by the gelatin present; even moreso, for true glace.

Edited by paul o' vendange, 10 January 2007 - 08:12 PM.

[Joisey]

I use dark chicken almost exclusively now. It's lighter on the palate and acts as a nice base for whatever you want. Plus it's easier dealing with chicken bones than it is with veal bones.

[scott123]

Wasn't it discussed in the thread on storing demi that much of the gelatin in stock is broken down in making demi?  I know not all, as the demi itself is quite thick, but I got the impression that demi is not a substantial source of gelatin.  Is this wrong?

I read the thread, but I'm afraid I can't agree. Gelatin is a breakdown product of collagen, but from what I know, gelatin itself is not heat labile; it survives heating quite nicely. If it didn't, glace would not be as thick as it is...

Looking through McGee on the subject:

Gelatin owes its remarkable properties to a peculiar amino acid makeup...which gives it a great affinity for water molecules, prevents its chains from coiling into more compact helical structures, and prevents the chains from coagulating when heated.  Some sauces, especially the concentrated, starchless reductions favored in the "nouvelle cuisine," owe their texture entirely to their gelatin content.

- i.e., classic espagnole based sauces would be aided by starch, and the imperfect proteins found in flour. But today's reduced stocks are almost entirely thickened by the gelatin present; even moreso, for true glace.

Gelatin slowly breaks down/loses it's ability to gel/thicken when heated. When exposed to the higher temps involved in reducing demi-glace and glace, this process is accelerated. Yes, demi is thick and glace is thicker and both do get their body from gelatin, but neither have the totality of body of the stocks from which they were made. A substantial loss of body/viscosity occurs.

Split a stock in half, make a demi with one part, then dilute that demi with enough water to match the volume of the other half. Chill. The water diluted demi will have a fraction of the gelling ability/mouthfeel of the unreduced stock.

The idea that prolonged heat damages gelatin's ability to gel/provide body is fairly well known. This is why you should simmer stocks until all the collagen is extracted but no further. If you keep simmering them indefinitely, the collagen will continue to break down and body will be lost.

From Dr. Bernard Cole, Food Scientist and Gelatin Specialist

It should always be remembered that heating, slowly destroys gelatin's gelling ability so one should always use the least amount of heating possible and for the shortest time possible.

From the Gelatine Manufacturers of Europe

Never add gelatine to boiling liquid because it loses its jelly strength.