I made a batch of chicken stock yesterday and cooled it by the method I
described in a prior thread. I place the stock pot on a 1 inch tall wire
grid trivet in the laundry tub, then fill the tub up with cold water to
about the level of liquid inside the stock pot. This time I got out my
digital thermometer and measured the temperatures a few times. I was
surprised at how fast the stock cooled... even faster than I had thought.

Here are the temperatures (in degrees F) of the stock and the cooling water
initially, after 15 minutes, and after 45 minutes:

Initial 15
Minutes 45 Minutes
Stock 160 85
75
Cooling Water 64 71
72

So most of the cooling took place within the first 15 minutes. At 45
minutes, it was essentially as cool as it was going to get (without changing
the cooling water). 75 degrees is pretty much room temperature. The rate of
cooling is going to change depending on the time of year and the temperature
of the incoming tap water. The greater the initial temperature difference
between the stock and the cooling water, the faster it will go. In mid
winter, my tap water was at 43 degrees, but I didn't measure stock cooling
at that time. In summer, my tap water will be even higher than it is now.

Some other parameters... the stock pot is a tall copper one, 8 inches in
diameter and 10 inches tall. There was between 3-1/2 and 4 quarts of stock
in the pot.

I suspect the results wouldn't have been quite so good with a low wide stock
pot, or one made of another material. With a low wide pot, I think there is
less surface area exposed to the cooling water, and there will be less total
cooling water in the tub. You can only fill the tub up to about the same
level as in the pot, or the pot will "float away". Using a trivet under the
pot is even more important on a low wide pot, as a greater percentage of the
available cooling surface area is on the bottom compared to a tall narrow
one.

I always strain the stock, then cool it. That is the method recommended in
all the cook books I have, and they also say not to cool totally covered or
the stock can turn sour. Regarding the initial stock temperature of 160
above, that is after straining, which cooled it off a bit. The temperature
coming off the stove was more like 170 (or even up to 180... I don't
remember what I saw).

--
( #wff_ng_7# at #verizon# period #net# )

"wff_ng_7" wrote in message
news:G2r1g.2526$_s5.1079@trnddc04...
I made a batch of chicken stock yesterday and cooled it by the method I
described in a prior thread. I place the stock pot on a 1 inch tall wire
grid trivet in the laundry tub, then fill the tub up with cold water to
about the level of liquid inside the stock pot. This time I got out my
digital thermometer and measured the temperatures a few times. I was
surprised at how fast the stock cooled... even faster than I had thought.
snip
( #wff_ng_7# at #verizon# period #net# )
In addition, I would recommend swirling the liquid in the pot every few
minutes either by swirling the entire pot or stirring with a spoon in order
to expose the hotter core of liquid to the cooler outer portion of the pot.
Janet

Janet Bostwick wrote:
"wff_ng_7" wrote in message
news:G2r1g.2526$_s5.1079@trnddc04...
I made a batch of chicken stock yesterday and cooled it by the method I
described in a prior thread. I place the stock pot on a 1 inch tall wire
grid trivet in the laundry tub, then fill the tub up with cold water to
about the level of liquid inside the stock pot. This time I got out my
digital thermometer and measured the temperatures a few times. I was
surprised at how fast the stock cooled... even faster than I had thought.
snip
( #wff_ng_7# at #verizon# period #net# )
In addition, I would recommend swirling the liquid in the pot every few
minutes either by swirling the entire pot or stirring with a spoon in order
to expose the hotter core of liquid to the cooler outer portion of the pot.
Janet

With an 8" dia. stockpot, I doubt this would make much difference. It
might in a wider pot, but if you got much of a temperature differential
within the pot, it would create a small current between hot and cold
and do the stirring for you. Might make you feel better though!

"salgud" wrote in message
oups.com...

Janet Bostwick wrote:
"wff_ng_7" wrote in message
news:G2r1g.2526$_s5.1079@trnddc04...
I made a batch of chicken stock yesterday and cooled it by the method I
described in a prior thread. I place the stock pot on a 1 inch tall wire
grid trivet in the laundry tub, then fill the tub up with cold water to
about the level of liquid inside the stock pot. This time I got out my
digital thermometer and measured the temperatures a few times. I was
surprised at how fast the stock cooled... even faster than I had
thought.
snip
( #wff_ng_7# at #verizon# period #net# )
In addition, I would recommend swirling the liquid in the pot every few
minutes either by swirling the entire pot or stirring with a spoon in
order
to expose the hotter core of liquid to the cooler outer portion of the
pot.
Janet

With an 8" dia. stockpot, I doubt this would make much difference. It
might in a wider pot, but if you got much of a temperature differential
within the pot, it would create a small current between hot and cold
and do the stirring for you. Might make you feel better though!

Undoubtedly I would feel as though I was contributing. ;o} Still, it would
be interesting to know whether the naturally forming currents would surpass
the artificially induced ones in efficiency.
Janet

The formula for heat transfer is:

Q/t = kA (Th-Tc)/d

Q/t is the rate of heat transfer, like Btu's per hour, k is the thermal
conductivity of the conducting material (like your copper pot), A is
the area the heat is being transferred across (square inches or square
feet usually), Th (the h should really be a subscript) is the
temperature on the hot side (inside your pot of broth), Tc (the c
should really be a subscript) is the temp on the cold side (in your
tub), and d is the thickness of the pot wall (probably in inches).

Basically, all the formula says is that the rate of heat transfer is
increased if the pot wall is a good conductor, like copper, by
increasing the temperature differential between the contents of the pot
and the contents of the tub, by increasing the area over with the
transfer is taking place or by decreasing the thickness of the wall in
between.

So all of the factors you mentioned come into play here.

For you scientific/mathematical types, since the temp of the broth is
constantly falling, this formula becomes a differential equation to
account for the fact that as the broth temp falls (and, if you want to
get really detailed, the temp of the water in the tub rising, maybe),
Th keeps changing. Fun stuff, for us nerds!


As I recall, altitude also plays some small part in this, as does static vs
moving liquids.

Larry T

Janet Bostwick wrote:
"wff_ng_7" wrote
I made a batch of chicken stock yesterday and cooled it by the method I
described in a prior thread. I place the stock pot on a 1 inch tall wire
grid trivet in the laundry tub, then fill the tub up with cold water to
about the level of liquid inside the stock pot. This time I got out my
digital thermometer and measured the temperatures a few times. I was
surprised at how fast the stock cooled... even faster than I had thought.

In addition, I would recommend swirling the liquid in the pot every few
minutes either by swirling the entire pot or stirring with a spoon in order
to expose the hotter core of liquid to the cooler outer portion of the pot.

That's just dumb... then most of the fat will remain with the stock
instead of rising to the top to solidify. And 4 quarts is not stock,
that's child's tea set cooking. And all those manual mashinations
contaminated whatever was in that pot... it's ALWAYS best to leave
stock cool undisturbed. There's really no reason to concern oneself in
how rapidly *sterile* stock cools. As far as culinarilly-wise this
was an exercise in lunacy. Don't yoose peeps have a life.



Sheldon

"Janet Bostwick" wrote:
In addition, I would recommend swirling the liquid in the pot every few
minutes either by swirling the entire pot or stirring with a spoon in
order to expose the hotter core of liquid to the cooler outer portion of
the pot.

I usually do that, but not this time... I was busy enjoying music on Foni
tis Helladas... otherwise known in English as the Voice of Greece, over
shortwave. Not a word of English, but great Greek music. Not that I
understand any of it, but that doesn't matter.

I did stir at the 15 minute mark, both in the pot and in the tub, but that's
all. I did also stir at the very beginning and end just to get accurate
temperature readings, but that wouldn't affect the cooling rate.

--
( #wff_ng_7# at #verizon# period #net# )

"salgud" wrote:
The formula for heat transfer is:

Q/t = kA (Th-Tc)/d
....

So all of the factors you mentioned come into play here.

For you scientific/mathematical types, since the temp of the broth is
constantly falling, this formula becomes a differential equation to
account for the fact that as the broth temp falls (and, if you want to
get really detailed, the temp of the water in the tub rising, maybe),
Th keeps changing. Fun stuff, for us nerds!

I actually did consider looking some of this up... my degree in mechanical
engineering covered at lot of this stuff... 30+ years ago. But a seat of the
pants analysis was enough! ;-)

--
( #wff_ng_7# at #verizon# period #net# )

Sheldon wrote:
Janet Bostwick wrote:
"wff_ng_7" wrote
I made a batch of chicken stock yesterday and cooled it by the method I
described in a prior thread. I place the stock pot on a 1 inch tall wire
grid trivet in the laundry tub, then fill the tub up with cold water to
about the level of liquid inside the stock pot. This time I got out my
digital thermometer and measured the temperatures a few times. I was
surprised at how fast the stock cooled... even faster than I had thought.

In addition, I would recommend swirling the liquid in the pot every few
minutes either by swirling the entire pot or stirring with a spoon in order
to expose the hotter core of liquid to the cooler outer portion of the pot.

That's just dumb... then most of the fat will remain with the stock
instead of rising to the top to solidify. And 4 quarts is not stock,
that's child's tea set cooking. And all those manual mashinations
contaminated whatever was in that pot... it's ALWAYS best to leave
stock cool undisturbed. There's really no reason to concern oneself in
how rapidly *sterile* stock cools. As far as culinarilly-wise this
was an exercise in lunacy. Don't yoose peeps have a life.


And your stock *stays* sterile as it cools down? What do you add to
it, Clorox?

--
Ernest

"Sheldon" wrote:
That's just dumb... then most of the fat will remain with the stock
instead of rising to the top to solidify. And 4 quarts is not stock,
that's child's tea set cooking. And all those manual mashinations
contaminated whatever was in that pot... it's ALWAYS best to leave
stock cool undisturbed. There's really no reason to concern oneself in
how rapidly *sterile* stock cools. As far as culinarilly-wise this
was an exercise in lunacy. Don't yoose peeps have a life.

I figured rfc's resident twit would eventually check in.

I challenge the twit to produce a well recognized (if not authoritative)
reference condoning his method. Why not start with showing that the stock is
sterile. Most recipes recommend temperatures well below the boiling point,
and even cooking at the boiling point does not guarantee sterility. Most
recipes also recommend cooling NOT covered.

--
( #wff_ng_7# at #verizon# period #net# )

salgud wrote:
Janet Bostwick wrote:
"wff_ng_7" wrote in message
news:G2r1g.2526$_s5.1079@trnddc04...
I made a batch of chicken stock yesterday and cooled it by the method I
described in a prior thread. I place the stock pot on a 1 inch tall wire
grid trivet in the laundry tub, then fill the tub up with cold water to
about the level of liquid inside the stock pot. This time I got out my
digital thermometer and measured the temperatures a few times. I was
surprised at how fast the stock cooled... even faster than I had thought.
snip
( #wff_ng_7# at #verizon# period #net# )
In addition, I would recommend swirling the liquid in the pot every few
minutes either by swirling the entire pot or stirring with a spoon in order
to expose the hotter core of liquid to the cooler outer portion of the pot.
Janet

With an 8" dia. stockpot, I doubt this would make much difference. It
might in a wider pot, but if you got much of a temperature differential
within the pot, it would create a small current between hot and cold
and do the stirring for you. Might make you feel better though!

When heating milk for yogurt, I use a pyrex 2-qt "cup", then cool the
yogurt down with a water bath in the kitchen sink. The 2 quart
container is about 8-9" across, and when I stand over it and gently
swirl the milk with the probe, the cooling takes about half the time of
allowing it to stand undisturbed.

Of course, that's only about 4" depth of liquid in there, so maybe that
would make a difference.

maxine in ri

"wff_ng_7" wrote in message
news:c9t1g.2541$_s5.2357@trnddc04...
"Sheldon" wrote:
That's just dumb... then most of the fat will remain with the stock
instead of rising to the top to solidify. And 4 quarts is not stock,
that's child's tea set cooking. And all those manual mashinations
contaminated whatever was in that pot... it's ALWAYS best to leave
stock cool undisturbed. There's really no reason to concern oneself in
how rapidly *sterile* stock cools. As far as culinarilly-wise this
was an exercise in lunacy. Don't yoose peeps have a life.

I figured rfc's resident twit would eventually check in.

I challenge the twit to produce a well recognized (if not authoritative)
reference condoning his method. Why not start with showing that the stock
is sterile. Most recipes recommend temperatures well below the boiling
point, and even cooking at the boiling point does not guarantee sterility.
Most recipes also recommend cooling NOT covered.

Why do you feel it needs to be sterile?

"ewdotson" wrote in message
ups.com...

Sheldon wrote:
Janet Bostwick wrote:
"wff_ng_7" wrote
I made a batch of chicken stock yesterday and cooled it by the method I
described in a prior thread. I place the stock pot on a 1 inch tall
wire
grid trivet in the laundry tub, then fill the tub up with cold water
to
about the level of liquid inside the stock pot. This time I got out my
digital thermometer and measured the temperatures a few times. I was
surprised at how fast the stock cooled... even faster than I had
thought.

In addition, I would recommend swirling the liquid in the pot every few
minutes either by swirling the entire pot or stirring with a spoon in
order
to expose the hotter core of liquid to the cooler outer portion of the
pot.

That's just dumb... then most of the fat will remain with the stock
instead of rising to the top to solidify. And 4 quarts is not stock,
that's child's tea set cooking. And all those manual mashinations
contaminated whatever was in that pot... it's ALWAYS best to leave
stock cool undisturbed. There's really no reason to concern oneself in
how rapidly *sterile* stock cools. As far as culinarilly-wise this
was an exercise in lunacy. Don't yoose peeps have a life.


And your stock *stays* sterile as it cools down? What do you add to
it, Clorox?

Sheldon is correct about repeatedly mixing the fat back into the broth. If
you don't mind finding globs of fat on the surface of everything you make
later with the broth, then stir away. As far as "sterile", why would you be
concerned about that? Nothing else in your world is sterile, except
bandages, until you open them.

"Doug Kanter" wrote:
I challenge the twit to produce a well recognized (if not authoritative)
reference condoning his method. Why not start with showing that the stock
is sterile. Most recipes recommend temperatures well below the boiling
point, and even cooking at the boiling point does not guarantee
sterility. Most recipes also recommend cooling NOT covered.

Why do you feel it needs to be sterile?

I don't.

It is Sheldon claiming that because it is sterile, therefore there are no
worries about organisms growing in it during a slow cooling process. I
believe in a prior thread Sheldon even proposed leaving the pot out on the
counter overnight. I don't believe the stock is sterile to begin with, and
any additional pathogens introduced by speeding up the cooling are not as
important as getting the stock out of the dangerous (fast growth)
temperature range as quickly as possible.

I have yet to see a good source condoning Sheldon's method. On the contrary,
I've come across numerous recognized and authoritative references advocating
quick cooling methods.

--
( #wff_ng_7# at #verizon# period #net# )

Doug Kanter wrote:
"ewdotson" wrote in message
ups.com...

Sheldon wrote:
[snip]

That's just dumb... then most of the fat will remain with the stock
instead of rising to the top to solidify. And 4 quarts is not stock,
that's child's tea set cooking. And all those manual mashinations
contaminated whatever was in that pot... it's ALWAYS best to leave
stock cool undisturbed. There's really no reason to concern oneself in
how rapidly *sterile* stock cools. As far as culinarilly-wise this
was an exercise in lunacy. Don't yoose peeps have a life.


And your stock *stays* sterile as it cools down? What do you add to
it, Clorox?

Sheldon is correct about repeatedly mixing the fat back into the broth. If
you don't mind finding globs of fat on the surface of everything you make
later with the broth, then stir away. As far as "sterile", why would you be
concerned about that? Nothing else in your world is sterile, except
bandages, until you open them.

It was Sheldon who brought up the sterility of his stock, not me. It
was that specific claim that I was addressing, as it struck me as
rather ludicrous.

--
Ernest