100 replies to this topic

[paul o' vendange]

Scott, that would be an interesting experiment. I do wonder, though, if it would be hard to detect any differences between a dilute demi-glace and non-reduced stock - whether it would or wouldn't exceed a sensory threshold. It would be interesting to send it to a lab and compare molecular weights.

All I speak from is my experience. My demi-glace was made over the course of 3 days - strong stock, day 1, remouillage, and final reduction/clarification; a total of 14 hours or so of simmering. If the gelatin was that heat labile, I would expect that on day 3 - when bones are no longer present, and collagen extraction was no longer taking place - the stock would thin, rather than thicken; I am not extracting any collagen any longer, but merely reducing. Even though we are evaporating water, if the gelatin was broken down, all we should end up with is less, thin stock, not a viscous demi or glace. Additionally, since collagen is preferentially labile when compared to gelatin, its breakdown product, I also wouldn't think it would remain in favor of that breakdown product.

I did find some interesting info in this regard:

Gelatine Use in the Dairy Industry

Among other things, what they write squares with my understanding:

Gelatine, with its unique molecular structure has some very interesting properties which are virtually unaffected by "denaturants" like modification of the thermal or charge environments, because the protein is already denatured.

(denatured from collagen).

From what I have read, it is true that gelatin undergoes thermo-labile destruction at temps higher than boiling (actually, from what I've read, high temps induce reformation to helical, collagen-like structure - not dissolution to simpler forms), such as are obtained under pressure; but at normal boiling, no such destruction occurs. See

Stanford Study - Properties of Gelatin

-A very interesting study on the chemical properties of gelatin, from the point of view of many stressors and conditions. Among other things, I think a concluding comment is relevant:

Thirdly, gelatin features a rather wide temperature range of the glassy state with the upper limit of 205°C-210°C. This characterizes gelatin as a material with a fairly wide range of heat resistance.

In the range of normal simmering, in particular, gelatin is shown to exhibit reversible properties:

In the second region (20° to 120°C) the behaviour of gelatin is mainly determined by its moisture content. The thermal contraction of cold and hot gelatin films observed in this temperature region (Figure 7) is not associated with relaxation processes since it is independent of the conformational state of gelatin macromolecules. Rather, it is in essence a purely physical contraction of samples caused by water desorption. This contraction is completely reversible on repeated moisturing of the gelatin and correlates well with the contraction caused by decreasing air humidity at room temperature1.

(In other words, at least as I read it, changes are not structural in nature - the coil structure is maintained - but rather due to water desorption; and even this change is completely reversible).

The article is a bit to go through, but it does square with my experience in the kitchen (again - I can only speak from my experience). Intuitively, the idea that gelatin is destroyed by prolonged simmering just doesn't intuitively register with me - the gummy "lip smack" of a glace, for instance, obtained after only truly prolonged simmering, tells me otherwise.

Edited by paul o' vendange, 11 January 2007 - 07:24 AM.

[paulraphael]

I don't know if gelatin breaks down in a way that reduces its thickening power, but it definitely runs the risk of developing unpleasant textures when it's over reduced. When making strong reductions for glace de viande, it's possible to end up with a sticky or gluey texture in the final sauce that is not present if you use greater quantites of less reduced glace.

It's also next to impossible to get the same luxurious texture that comes from coulis thickened by multiple immersions (tripple jus, for example) but which are too expensive for most people to consider.

A bigger issue for me is the loss of subtle, volatile flavor components from extreme reduction. I tend to prefer a traditional demiglace (made with a fair amount of meat in the stock, slightly thickened with starch and moderate reduction) over highly reduced glace, for this reason.

[paulraphael]

... and making your own is worthless, because you throw away too much to spoilage.

You believe there's a problem with freezing it?

[paul o' vendange]

I don't know if gelatin breaks down in a way that reduces its thickening power, but it definitely runs the risk of developing unpleasant textures when it's over reduced. When making strong reductions for glace de viande, it's possible to end up with a sticky or gluey texture in the final sauce that is not present if you use greater quantites of less reduced glace.

It's also next to impossible to get the same luxurious texture that comes from coulis thickened by multiple immersions (tripple jus, for example) but which are too expensive for most people to consider.

A bigger issue for me is the loss of subtle, volatile flavor components from extreme reduction. I tend to prefer a traditional demiglace (made with a fair amount of meat in the stock, slightly thickened with starch and moderate reduction) over highly reduced glace, for this reason.

I agree with you, Paul. Not only an overreduced stock, but the rate at which it reduces matters, in my book - too fast a reduction, and the localized heating is too radical - the stock tastes harsher than is obtained when a simmering reduction is more gently pursued. Depending on what I am doing, I may do a double stock (never done a triple, for cost reasons, as you mention), or even a classic sauce from espagnole. I have found the remouillage method I've adopted from Thomas Keller's technique yields a wonderful, velvety, impeccable mother stock for many applcations.

[coquus]

... and making your own is worthless, because you throw away too much to spoilage.

You believe there's a problem with freezing it?

Sorry Paul, I've been on vacation. I don't know the science behind it, but it gets freezer burnt eventually, especially when reducing it's surface area into ice cubes as some have suggested. I wouldn't freeze glace de viande (or whatever you would call the way I make it), firstly because it doesn't need to be frozen when made properly, and secondly because my freezer space is at a premium .

[begpie]

i want to know the best way to thicken a espagnol sauce or demi glace besides reducing it?

[DTBarton]

I like to mix softened butter with flour in a small bowl with a whisk. Pick up some of the mixture on the whisk and stir it into the simmering sauce. Adds a little richness in addition to thickening.

[begpie]

I like to mix softened butter with flour in a small bowl with a whisk.  Pick up some of the mixture on the whisk and stir it into the simmering sauce.  Adds a little richness in addition to thickening.

but it interferce with the colour

[paulraphael]

i want to know the best way to thicken a espagnol sauce or demi glace besides reducing it?

I've had good luck reducing just to the point where the flavor is right, and then adjusting the consistency with arrowroot starch (starting with 1/2 tsp per quart, made into a slurry with a bit of cool water. It thickens the sauce after a low simmer for a minute or so. Be sure to test consistency by drizzling onto a cool plate.

For my last couple of batches of demi, I've moved away from the reduced espagnole method, and experimented with modern methods that are really an update of 17th and 18th century meat coulis.

Time requirement is about the same, and food costs are lower. I like the results much more. The technique is appropriate for a glace that has a distinct meaty flavor; it will not always substitute for more neutral glaces (reduced veal stock, etc).

Recipe is here: http://recipes.egull...ipes/r2081.html

[ChrisTaylor]

I'm looking at Escoffier's recipe for demi-glace (which I'll be using as a base for his Madeira sauce). He mentions finishing the sace with 'one-tenth of a quart of excellent sherry'. What kind of sherry would he be using? Or rather, what kind of sherry should I use? A fino is going to a very different outcome to, say, an oloroso.

[TheTInCook]

I'm looking at Escoffier's recipe for demi-glace (which I'll be using as a base for his Madeira sauce). He mentions finishing the sace with 'one-tenth of a quart of excellent sherry'. What kind of sherry would he be using? Or rather, what kind of sherry should I use? A fino is going to a very different outcome to, say, an oloroso.

I'm going to hedge my bets and say probably amontillado, and definitely not a fino or one its derivatives.