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nathanm

Cooling rates in water baths, ice baths, etc.

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<span style='font-size:8pt;line-height:100%'>HOST'S NOTE: The main Sous Vide topic spawned this interesting discussion of cooling rates: since it was not directly related to Sous Vide and has info useful to chefs in many areas of cooking we have split it into its own discussion.</span>

The only other reason I can think of for multi-stage cooling (before storage) is to let the core temp reach the desired cooking temp in cases when you've been cooking in a water bath significantly above your desired cooking temp. This is related to the "resting time" in the tables that Nathan has previously posted (e.g. here). For example, as in the table, if you had a 100mm (~ 4-inch) steak cooking in a 65 C (149 F) water bath, you would want to take the steak out of the bath after 2 hours and 50 minutes, when its internal temp is 124.8F. It would then take a further 33 minutes and 10 seconds for the core of that steak to reach 130F, the desired final cooking temp. (Not sure if Nathan's calculations had the bag resting at ambient temp in air or with a no heat flow boundary condition, though the specific boundary condition may not make much of a difference.)

Nevertheless, if you were to pull said steak out the ice bath at 2 hours and 50 minutes, and plunge it immediately in an ice bath instead of letting it rest for 30 minutes, the core temp wouldn't reach 130 F. It would only reach desired temp of 130F if you did multi-stage cooling, e.g. let rest at room temp in air, then put it in ice water. (Of course, you could redo all the calculations to assume that you were letting the bag "rest" in ice water, but we're crossing the line into absurdity here...)

This is a common fallacy in thinking about heat transfer.

Suppose you cook food for a period of time in a bath at temperture T1, then you move to a bath at T2, or the air in the room, or anything.

The peak core temperature from the initial cooking at T1 will in general continue to rise for a bit after removing it from the bath - that is the rest time.

If T2 < T1, i.e. you move it from a hot bath to a less hot bath, then after a while the core temperature will drop.

HOWEVER, the peak value does NOT depend on T2. There is no difference between dropping it in liquid nitrogen, or putting it in a bath that 1 degree below T1. As long as T2 < T1.

This fallacy usually presents itself in the form of saying "plunge the food into ice water to stop the cooking". Nope, doesn't work. Plunging it in ice water will chill the food quickly but it will reach the same peak temperature.

The reason this is true is that the speed with which heat diffuses through food (or any solid) is fixed by the material. When you put the food in a colder bath, it starts to draw heat out of the food into the bath, but it can't speed up and overtake the heat you were putting into the food earlier.

Loosely speaking the "heat wave" that you push through the food while cooking cannot be overtaken by the "cold wave" from chilling because they travel at the same speed.

Our instinctive notion is that if it is really cold then it will somehow travel faster. This is like thinking that a heavier object will fall faster. Well, as Galileo showed all objects fall at the same speed. And all heat travels at the same speed.

If T2 > T1, then peak caused by the initial cooking at T1 will still peak the same time, but then after that it will rise due to additional heat from T2.

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I know I'm quoting a rather old post, but I recently had an interesting discussion with a chef who uses the CS (Cuisine Solutions) system.  It seems that the reason for cooling ``successively, at room temperature, in cold water, then in ice water'' is to allow the meat time to absorb some of the liquid in the bag.  My initial tests seem to confirm this. 

This might happen but I am pretty skeptical.

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....

HOWEVER, the peak value does NOT depend on T2.  There is no difference between dropping it in liquid nitrogen, or putting it in a bath that 1 degree below T1.  As long as T2 < T1.

This fallacy usually presents itself in the form of saying "plunge the food into ice water to stop the cooking".  Nope, doesn't work.    Plunging it in ice water will chill the food quickly but it will reach the same peak temperature.

The reason this is true is that the speed with which heat diffuses through food (or any solid) is fixed by the material.  When you put the food in a colder bath, it starts to draw heat out of the food into the bath, but it can't speed up and overtake the heat you were putting into the food earlier.   

You might well be correct about the relative uselessness of multi-stage cooling in the case under discussio, but I believe that your characterization of how heat transfer works is not quite correct. There are certainly cases where the temperature of the bath (and the bath's specific heat, and other factors) can influence the final core temperature. There are quite a few relevant variables. The size of the object being heated/cooled. The temperature differential between the exterior and the core. The relative specific heats of the cooling medium and the object being cooled (I.e. if you are cooking in a bath that is significantly higher than the desired core temperature there will be a larger differential between the exterior temp and the core temp and if the piece of meat is sufficiently large, the temperature and specific heat of the cooling bath might influence the final core temp).

In practical terms, in this application, it may be true that the baths temperature won't have an impact on the core temperature. But the notion that the cooling bath's temperature is irrelevant does not seem right unless we are talking about either small pieces of meat or cooking in a bath only slightly warmer than the desired core temp. In which case, the core is going to be so close to the final temp that you are correct in practical terms.

If you had a large piece of meat, where the core was at a considerably lower temperature than the outer part of the meat -- dropping it in liquid nitrogen would (or an ice-water bath for that matter) would result in a different maximum core temp than dropping it in a bath that was 1 degree cooler than the meat.

Heat is kinetic energy. Hot and cold are just relative amounts of kinetic energy. Hot molecules are moving more than cold molecules. When the hot and cold molecules collide, the kinetic energy equalizes. So, a molecule at 150 degrees that bumps into a molecule that is 40 degrees is going to lose a lot more heat than if it had bumped into a 149 degree molecule. In turn, the hot molecules that the cooled molecule bumps into are going to cool down more too.

If an object is dunked in an ice-water bath, its outer layers are going to cool off a lot more in a given period of time than if dunked in a bath that was warm. Those layers in turn are going to steal heat from the inner layers,etc.

Anyway, I think that this is the case. Apologies if the squirming newborn in my arms has muddled my thinking.

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...

This fallacy usually presents itself in the form of saying "plunge the food into ice water to stop the cooking".  Nope, doesn't work.    Plunging it in ice water will chill the food quickly but it will reach the same peak temperature.

The reason this is true is that the speed with which heat diffuses through food (or any solid) is fixed by the material.  When you put the food in a colder bath, it starts to draw heat out of the food into the bath, but it can't speed up and overtake the heat you were putting into the food earlier.   

Loosely speaking the "heat wave" that you push through the food while cooking cannot be overtaken by the "cold wave" from chilling because they travel at the same speed.

Our instinctive notion is that if it is really cold then it will somehow travel faster. This is like thinking that a heavier object will fall faster.  Well, as Galileo showed all objects fall at the same speed.  And all heat travels at the same speed. ...

Ummm, NathanM, I'm a bit troubled by the physics of this.

And the implicit confusion between "heat" and temperature.

I don't see gravity as being any sort of analogue for thermal transfer.

Which means there's some false logic (a "fallacy" :hmmm: ) in associating Galileo's proposition with yours!

"All heat travels at the same speed" (even in the same material) has to be an oversimplification in the discussion of the size of temperature transients.

I'd suggest that it is perfectly possible that the time before the central temperature peaks is indeed not going to be affected by the application of a surface chill. (If it actually 'peaks' at all, see below!)

However, the time to peak, and the size of the peak are very different questions.

It seems to me that the quantity of energy that reaches the centre (to raise its temperature) is going to be less, and thus the peak core temperature would be lowered, by a greater external chill application.

If we think of your "heat wave" as an energy pulse, then because of the chill, energy from the pulse is being 'bled away' towards the cooled surface - leaving less energy to progress to the centre.

If there is a thermal gradient (temperature difference) then heat energy will flow - in proportion to that temperature difference (and distance - to give the gradient). And as long as the outside is cooler than at the 'wave crest', then some energy must flow back out of the wave, out of the testpiece.

That "heat wave" has no momentum. Its only reason to move is temperature difference. Change the temperature gradient that drives the flow and you immediately change the rate (even the direction) of energy flow.

The units of thermal conductivity are something like watts per metre per degree Kelvin. Heat energy will flow down any temperature gradient.

So, after a specific amount of heating, the greater the external chill applied, the greater the rate of energy flow to the outside, leaving less heat energy to flow towards the centre, and so the less the peak temperature of the core will be.

In extremis, with a 'thick' testpiece, a 'brief' heat pulse and 'prolonged, intense' chilling, the core temperature might not actually rise at all before it starts to chill... because, (effectively) all the pulse's energy has preferentially flowed to the very cold outside rather than the merely cool centre. More heat energy will flow in the direction of the greater temperature gradient. (EDIT - gradient, not "difference".)

Hence it would seem that chilling the surface of a heated (but not equilibrated) testpiece DOES have the potential to affect the peak temperature experienced at the centre.

However, I must say that the whole application of non-equilibrium cookery concepts to sous-vide methods does seem to me to be missing the main point - the control to be able to cook things to a precise degree ( :biggrin: or fraction of a degree!)

That said, I really have no idea whether gradual or crash cooling would result in the meat/fish ultimately retaining more of its own juices. My suspicion (for what little its worth) would be that there could be little ultimate difference if it were then to be reheated in the same bag/juices before service.


Edited by dougal (log)

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Ummm, NathanM, I'm a bit troubled by the physics of this.

And the implicit confusion between "heat" and temperature.

Hence it would seem that chilling the surface of a heated (but not equilibrated) testpiece DOES have the potential to affect the peak temperature experienced at the centre.

Sorry, but this is the way it works. Your physical reasoning is wrong.

You are certainly correct that heat and temperature are not the same thing. I clearly said in my earlier post that I was speaking loosely.

You are also correct that this only applies to non-equilibrium cooking, where you use a bath temperature that is hotter than you want to achieve for the final. I totally agree that this is a bad idea that misses much of the point of SV.

As to the physics I don't have time right now to give the full treatment, but trust me it really is the case. You have written a heat equation simulator, as I have - try it out and it will tell you exactly what I am saying (i.e. make the boundary conditions switch from T1 to T2 at time t, and see what happens for various T2 in relation to T1.)

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If an object is dunked in an ice-water bath, its outer layers are going to cool off a lot more in a given period of time than if dunked in a bath that was warm. Those layers in turn are going to steal heat from the inner layers,etc.

Of course, but it takes time for the temperature difference to diffuse to the center. There is already a gradient of temperature difference in layers all the way from the surface to the core. Those interior layers will equilibrate the core before temperature stealing from the surface has time to get to the core.

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I am still pressed for time so will be brief, but here are two graphs of a simulation that shows the peak phenomenon.

The case shows here is that you take several steaks steak which are 30 mm thick.

They start at a uniform 5C. First, the steaks go into a bath at T1 = 70C. At exactly 1100 seconds, the steaks are removed and put in a second bath at T2 = 1C, 10C, 20C, 30C. One is left in the 70C bath.

The first graph shows what happens at the center of the steak.

gallery_9517_6181_11902.jpg

The blue line shows the steak that stays in the bath and is not removed. It finally equilibrates to 70C at about 4000 seconds (a bit over an hour).

Each of the other lines shows what happens to steaks in the various second baths. They are also approaching equilbrium at the second bath temp, after about an hour.

This graph shows a close up of what goes on in the transition between the two baths.

gallery_9517_6181_17607.jpg

At 1100 seconds we take the steak out of the first bath at T1 and put them in the second baths at T2. At that point the the core temperature of each steak is 50.08C.

It takes a while for the center to even notice that anything has changed. Each of the lines representing a different bath has a SLIGTHLY different peak temperature (marked with dots the same color as the lines), at a slightly different times. However, for all practical purposes they are the same.

The 30C bath steak peaks at 1246 seconds (146 seconds after moving to the second bath). The 1C bath peaks at 1216 seconds - or exactly 30 seconds sooner than the 30C bath, or about 2.5% of the total time. The others baths are in between the 30C and 1C cases.

The peak temperatures are very close - 52.3 for the 1C second bath, and 52.67 for the 30C second bath, for a difference of only 0.37C, which is of zero practical importance. A difference of 29C between the baths produces a 0.37C difference in peak temperature. The difference in the peak is a factor of 78X smaller than the difference in the second bath temperatures.

Somebody might object that in posts above I say that the peak would be the same, while these are different.

First there is no practical difference for chefs. 0.37C is less than measurement error for all but the most expensive calibrated thermometers. It makes no difference you can taste in food.

Second, the tiny difference that is shown here is primarily due to a mathematical approximation that I am using. I am assuming that I can switch the baths infinitely quickly, and bring the surface of the steaks to the new bath temperature very quickly. This is nearly true, but of course not quite. This approximation creates some unrealistically fast cooling right at the surface of the steaks, which contributes the 0.37C difference in peak temperature.

Later on when I have more time I will do a better simulation that will account for this more realistically, but I don't have time to do that now.

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Nathan, thank you for troubling to to that.

It does show the type of effect that e_monster and I had envisaged -- but as you say, the size of the effect is quite small.

Regarding my own 'feel' for what is happening, I think that the specific heat must be lower in proportion to the conductivity than I'd have expected - hence there is rather less heat stored within the steak, and the effect of the chill is felt much faster. And I was being guided by my personal experience of watching the size and duration of the temperature overshoot when poaching hams, rather than 15mm-to-the-middle steaks. A (quasi-cylindrical) chunk of ham even brings in different geometrical considerations...

The graphs show that, even after 18 minutes 20 seconds of heating, removing the bag from the 70C bath to a (hot-kitchen temperature) 30C bath, the core temperature only rises/overshoots by a mere 2.6C. And peaks just two and a half minutes (146 sec) after heating ceased.

And that is indeed way less overshoot, and peaking quicker, than I'd have guessed (but then I wasn't thinking specifically of steaks).

Since the graph's figures indicate that ice bath chilling (instead of hot kitchen ambient) reduces the steak's further rise from 2.59 to 2.22C - a 14.3% reduction in "overshoot" temperature - and the time to peak dropping from 146 to 116 seconds - a 20.5% reduction - I'd say that the effect we expected is indeed there, but that it, and the whole 'overshoot', is much smaller than I, for one, was thinking of.

Hence I have no hesitation in agreeing that, for inch-thick steaks, it it does appear of little practical consequence to the peak core temperature whether they were to be chilled in a room temperature bath or in an iced-water bath.


Edited by dougal (log)

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This is a common fallacy in thinking about heat transfer.

Suppose you cook food for a period of time in a bath at temperture T1, then you move to a bath at T2, or the air in the room, or anything.

The peak core temperature from the initial cooking at T1 will in general continue to rise for a bit after removing it from the bath - that is the rest time.   

If T2 < T1, i.e. you move it from a hot bath to a less hot bath, then after a while the core temperature will drop.

HOWEVER, the peak value does NOT depend on T2.  There is no difference between dropping it in liquid nitrogen, or putting it in a bath that 1 degree below T1.  As long as T2 < T1.

This fallacy usually presents itself in the form of saying "plunge the food into ice water to stop the cooking".  Nope, doesn't work.    Plunging it in ice water will chill the food quickly but it will reach the same peak temperature.

So, taking this back to practical application: is there *any* reason to cool vegetables in an ice bath after cooking sous vide at target temperature? I think many of us do so because we're accustomed to a blanch/shock treatment in traditional vegetable cooking, but it sounds here like if you're cooking at your target temp, it's accomplishing very little.

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So, taking this back to practical application: is there *any* reason to cool vegetables in an ice bath after cooking sous vide at target temperature?  I think many of us do so because we're accustomed to a blanch/shock treatment in traditional vegetable cooking, but it sounds here like if you're cooking at your target temp, it's accomplishing very little.

Yes there is a reason - you chill the food quicker.

Chefs are typically taught that you "shock" the food to "stop the cooking". This is wrong - the degree of cooking is generally determined by the peak temperature and that is basically unaffected by a cold water shock.

However, the food does chill faster in cold water. If you are doing cook-chill sous vide where you want to store the food cold then this helps with food safety. You want to chill as fast as you can in that case.

If you look at the graphs in the post above you can see that the 1C cold bath gets colder faster than the 10C. In the case of the 30mm steak they each take about an hour to chill completely to the bath temperature.

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Even so, I'm not so convinced that this is needed for sous-vide cooking, provided the integrity of the bag is OK.

For almost all SV cooking the food has been (mostly) sterilised to at lesat the reccomended FDA time/temperaature for cooked foods and at least to the level where it could be safely held for several hours (4.6 hours at 44C to 16 hours at 20C, extrapolating from the FDC data), providing the bag does not leak or is opened or the food otherwise exposed to new pathogens.

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Here is a graph for a cube of meat 125mm on a side. This is like a roast. I know that most roasts are not perfect cubes, but this shows a case that is much thicker than the 30mm thick steak in previous.

Once again the meat starts at 5C and is in a bath at T1 = 70C. It takes much longer to reach temperature - about 25,000 seconds or 7 hours to reach 70C.

At 7500 seconds (2 hours and 5 minutes) we switch the roasts from the first bath to second bath at T2 = 1C, 10C, 20C, 30C.

gallery_9517_6181_3394.jpg

Here is detail near the peak.

gallery_9517_6181_12332.jpg

The core temperature at the time of the bath switch is 45C. The 30C bath peak is 53.16C, the 1C bath peak is 52.19, for a spread of just under 1C. This is still insignificant for any cooking application.

The total overshoot from the time the meat is taken out of the first bath to the peak is quite significant - it is 8.26C for the 30C bath. If this was a beef roast, it would be warm but raw at (45C, or 113F) with no color change, but would be cooked to rare at 53C / 128F.

The peak temperature happens at about 33 minutes after switching to the 1C bath and about 41 minutes after switching to the 30C bath, for a spread of about 7.6 minutes.

So, this works for 30mm steaks. It works for 125mm roasts. I have checked this for thicknesses from 5mm to 150mm.

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Even so, I'm not so convinced that this is needed for sous-vide cooking, provided the integrity of the bag is OK.

For almost all SV cooking the food has been (mostly) sterilised to at lesat the reccomended FDA time/temperaature for cooked foods and at least to the level where it could be safely held for several hours (4.6 hours at 44C to 16 hours at 20C, extrapolating from the FDC data), providing the bag does not leak or is opened or the food otherwise exposed to new pathogens.

There are several issues to consider here:

- If your goal is to cool the food down to refriderator temperature, then doing it quicker is going to help food quality (a little) and help food safety (a little).

- Ice water is pretty cheap and available in the kitchen so it is not a big deal.

- You avoid overheating other things in your refriderator. Most fridges are designed to maintain temperature - putting hot food into the fridge strains the cooling capacity, and will warm up other food nearby.

- Technically speaking, the FDA rules allow 4 hours of time in the so called "danger zone" between cooking temperature and 5C. You are correct that if you extrapolate the acutal amount of time depends on temperature, and you can hold much longer at 20C than at 44C. However, that is "just" scientific reality. The actual health inpspector is taught 4 hour maximum holding time.

In the case of the 125mm cube roast that I posted above it does not actually make it within 4 hour time limit - but is close enough.

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One point that I should clarify in the posts above.

I used two WATER BATHS - one at 70C and the other at 1C, 10C, 20C, 30C.

This is NOT the same as taking the food out and leaving it in air in the kitchen! The reason is that heat transfer from air to a solid, via natural convection, is quite slow. It is about 100X less effective than stirred water.

Natural convection in air (i.e. not forced with a fan) will transfer about 20 watts per square meter, per degree C of temperature difference.

A stirred water bath will transfer about 2000 watts per square meter per degree C of temperature difference.

So, the cooling curves for leaving the steak or roast out in the kitchen air at 20C are NOT the same as for putting into a water bath at 20C. The air will be MUCH slower.

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So, taking this back to practical application: is there *any* reason to cool vegetables in an ice bath after cooking sous vide at target temperature?  I think many of us do so because we're accustomed to a blanch/shock treatment in traditional vegetable cooking, but it sounds here like if you're cooking at your target temp, it's accomplishing very little.

Yes there is a reason - you chill the food quicker.

Chefs are typically taught that you "shock" the food to "stop the cooking". This is wrong - the degree of cooking is generally determined by the peak temperature and that is basically unaffected by a cold water shock.

However, the food does chill faster in cold water. If you are doing cook-chill sous vide where you want to store the food cold then this helps with food safety. You want to chill as fast as you can in that case.

Right, that's why I was wondering if there was any value in chilling if you're cooking vegetables, where food safety is not a big issue?

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This is getting somewhat out of the topic of sous vide, but I would imagine it may have to do with reactions and effects that are both time and temperature dependent.

In a piece of beef tenderloin, for example, 30 minutes at the temperature of medium rare is not much different from 3 seconds at the temperature of medium rare. The meat will have the "doneness" of medium rare.

In some vegetables, however, there may be some advantage to taking it up to a certain temperature range and then back out as soon as possible. A stalk of asparagus that is taken out of simmering water and plunged into an ice bath will spend not very much time at high temperature. A stalk of asparagus that is taken out of simmering water at the same time and simply placed on a platter will spend considerably more time at high temperature. This may mean that the non-chilled stalk of asparagus will have more cell wall degradation, etc. and a consequently softer texture.

This is just a guess.

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Sam:

Not quite.

In meat the denturing of collagen to gelatine, while temperature dependent is a slow process, so the meat kept at temperature for 30mins (or more like 12 hours) will be much more tender than the 3 second piece.

In vegetables its the same slow heat transfer to the interior effect. Simmering water is at about 95C, and I suspect its not time at temperature that is causing the softening, but heat transfer to the interior causing more of the inside to soften.

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Jack, I don't think you read my post carefully enough.

My example of beef specifically mentioned tenderloin because it is a tender meat. There should be minimal difference, if any, between a beef tenderloin cooked to 55C for 3 seconds or 30 minutes. Both will be medium-rare, and both will have the same tenderness.

A brisket cooked to 55C for 30 minutes versus 30 hours... yes, there will be a difference in texture. However, both will still be at the same level of "doneness" (medium rare).

Vegetables are different. Texture and "doneness" are usually the same thing.

I am hypothesizing that a vegetable blanched in 95C water for a fixed period of time and left on a platter will have a softer texture than one which is chilled in an ice bath. I may be incorrect about this, however.

Nathan's charts indicate that the vegetable will reach the same peak core temperature regardless of whether the vegetable is chilled in an ice bath or not. So, if it is the case that the unchilled vegetable is softer than the chilled vegetable, then it cannot be due to a difference in core temperature. The only thing that differentiates the two vegetables, then, would be time-at-temperature, with the unchilled vegetable spending significantly more time in the higher temperature range.

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Sam:

Not quite.

In meat the denturing of collagen to gelatine, while temperature dependent is a slow process, so the meat kept at temperature for 30mins (or more like 12 hours) will be much more tender than the 3 second piece.

In vegetables its the same slow heat transfer to the interior effect. Simmering water is at about 95C, and I suspect its not time at temperature that is causing the softening, but heat transfer to the interior causing more of the inside to soften.

In my experience, time at temperature definitely has an effect on vegetables CSV, though it's a slow process. Carrots cooked for 2 hours vs 1 hour are uniformly more tender, through to the core. For most vegetables though, I don't think the time spent resting out of the bath making much additional difference. Not sure about asparagus.

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That seems to be a fairly clear cut experiment then.

Aspargus is out of season here. Lets use say broccoli stalk, one piece cut into two.

So simmer for say 3 mins.

Shock one piece, and leave the other on a plate for say 30 min

The hypothesis is that they will be of different softness, and that suggest time-at temperature is important.

If they are the same softness it might suggest time at temperature is not.

Lets hope as many people try as can, and report here.


Edited by jackal10 (log)

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The more I think about this, the more I suspect I am correct about time-at-temperature. Think about cooking, say, some broccoli pieces in 95C water. After you put the broccoli in the water, how long can it possibly take before the core temperature of the broccoli is approximately 95C? Certainly no more than a minute. And yet, if you pull the broccoli out of the water after 1 minute, it will still be fairly crisp. Leave the broccoli in the water for 5 minutes, and it will be soft. What's the difference? Time-at-temperature.

For cooling in ice water versus cooling in air, it may be that the difference in time-at-temperature is not significant enough to make a difference. Which would suggest that cooling blanched vegetables in ice water is a waste of time. As Jack suggests, it should be a fairly simple experiment.

Additionally, as Al suggests, there may be no benefit gained in chilling vegetables that have been cooked SV at lower temperatures.


Edited by slkinsey (log)

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That seems to be a fairly clear cut experiment then.

Aspargus is out of season here. Lets use say broccoli stalk, one piece cut into two.

So simmer for say 5 mins.

Shock one piece, and leave the other on a plate for say 30 min

The hypothesis is that they will be of different softness, and that suggest time-at temperature is important.

If they are the same softness it might suggest time at temperature is not.

Lets hope as many people try as can, and report here.

We should also control temperature in this experiment, as there are some temperature-dependent processes at play. I believe pectins begin to break down at 85C. I generally cook most vegetables sous vide at 82C.

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For cooling in ice water versus cooling in air, it may be that the difference in time-at-temperature is not significant enough to make a difference.  Which would suggest that cooling blanched vegetables in ice water is a waste of time.  As Jack suggests, it should be a fairly simple experiment.

The other reason commonly given for the ice water shock is to set the color of the vegetables. This seems scientifically plausible, as this is a surface reaction: ice water may effectively prevent chlorophyll on the surface from denaturing. So ice-water shocking blanched veggies may not be a complete waste of time. :)

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I tried it, and on the basis of one piece of broccoli, I could tell no difference.

There may be a mass effect, lots of broccoli together I would expect to stay warmer longer.

If a critical temperature for cooking vegetables is 85C, then that is not that different from 95C, and small temperature differences may be more important.

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Nathan - just a quick question about the simulation. We know that the meat loses water as it cooks. Is there a difference between the specific heat of cooked vs raw meat? If so, would its magnitude effect the simulation?

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