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This propellant got its name because it has the appearance and
characteristics of caramel candy. It is made with table sugar, it is
heated, and though we all would (at least I would) like it to be pure white,
it usually ends up the color of caramel. It is thick and gooey like
the candy in the making, too. The difference, of course is the real
candy won't burn like a propellant and the real propellant doesn't taste
like candy, and of course isn't to be eaten. It is also known as
R-candy or rcandy rocket propellant or fuel. It should be obvious that
the "R" stands for rocket.
The basic formula is made from just two components, an oxidizer and a fuel.
The oxidizer is potassium nitrate. Its chemical formula is KNO3.
(note: "K" is the official chemical designation for potassium).
You will often see in rocketry web sites "KN" used for potassium nitrate. The fuel is table sugar -- sucrose. Its chemical
formula is C12H22O11. Like KN,
a shortened designation Su will often be used on rocketry web sites
like those related to homemade rocket engines (motors) or homemade rocket
fuel or propellant. The
fuel on these web sites will often be referred to as KNSu rocket fuel
Sucrose, or table sugar, was the first sugar to be used. Dextrose is a better choice as
it has a little lower melting point. Sorbitol is quickly becoming the
most serious sugar used because of its lower melting point and slower curing
time (and so longer pot life). It is also less prone to cracking in
larger motors. Sucrose when used with corn syrup such as Karo can also be
made less brittle and is becoming more popular primarily through the efforts
of Jimmy Yawn (the originator of using corn syrup in propellant???) and Dan
Pollino who has made J & K motors with it. Examples of other sugars and sugar
substitutes that have been experimented with are: fructose, maltose,
lactose, erythritol and xylitol. Scott Fintel successfully launched an
"O" motor rocket using erythritol as the sugar. Discussions on this page refer only
to sucrose unless specified otherwise but much on this page is applicable to
any sugar/potassium nitrate propellant.
Propellant formulas (as are all chemical formulas) are determined by weight.
The theoretical best performance is 66% KN, 34% Su. However, the
standard formulation that most everybody uses (including myself), is 65%
KN, 35% Su. According to Richard Nakka, a formula of 60% KN, 40%
Su, can be used and he suggests people new to the propellant should start
with this ratio. This lower KN percentage formula is thinner and so
easier to load into grain forms and also has less tendency to caramelize.
I haven't experimented with the lower KN percentage formula yet ( as of
9-9-06) but it is on my to-do list.
When searching the internet you will find a variety of slight variations to
the percentages of Potassium Nitrate and Sugar. You will also find additional components
Corn syrup used in sugar propellant could (and may in the future) have its
own dedicated web page. It is a bit mysterious but definitely has an
interesting effect when used as an ingredient in sugar propellants.
Corn syrup is used in baking in place of sugar to make the baked item softer
where sugar would make the product more crisp. The reason is that corn
syrup resists crystallizing. When propellant is made, crystallizing is
part of the process. It is heated either with water or dry but either
way, the sugar becomes molten or dissolved and is in an uncrystallized
state. If water is used, the water is first driven off. Then in
either case, when it cools, the propellant recrystallizes. When Jimmy
Yawn talks about his recrystallization process, it is not something unique
to his method. All heated sugar propellants uncrystallize, then are
cast, and at that point recrystallize.
The fact that corn syrup does not crystallize in the normal state is the
very reason it is used in sugar propellants. The grains need to be
solid but the undesirable aspect is their brittleness which comes about
because both the sugar and potassium nitrate are crystalline at
normal temperatures. By introducing corn syrup which at normal
temperatures is not only not crystalline but not solid, the brittleness is
One note is that sucrose and dextrose both start the caramelization process
at 320°F so to prevent loosing the
advantages of corn syrup, temperatures during processing should be held
below that temperature. Caramelization is a process that breaks down sugar
into other chemicals and turns a darker yellow-brown color.
Caramelization somewhat degrades the power of the propellant. See my
caramelization page for more details.
What is corn syrup?
If the answer to that was easy, it might eliminate some experimentation.
You would think that you could just look it up somewhere and find that it
was composed of certain ingredients in certain amounts but that isn't the
case. It isn't made in a chemistry lab from specific ingredients, it is derived from an organic source (corn is only one possibility) and its
exact makeup can vary between manufacturers and products. Essentially,
it is a combination of dextrin, maltose, and dextrose. Glucose and
dextrose are the same thing, just different names. As a matter of
fact, corn syrup is sometimes called glucose syrup, especially outside the
USA. Dextrin is not the same as dextrose, it has one less water
molecule in the formula. There are also different kinds of dextrose
depending on how the molecules are arranged. Corn syrup can have
sucrose added to it. Corn syrup can be processed further to create
fructose (which has the same chemical formula as dextrose but with a
different arrangement of the atoms) and then that can be added to regular
corn syrup. Other sugars like maltose are also found in lesser amounts
in corn syrup. So, how much dextrose, how much dextrin, how much
sucrose, and how much fructose is in the corn syrup you are using? You
will never know. My Karo© light corn syrup has as ingredients: light corn syrup, high fructose
corn syrup (there are several types ranging from 90% fructose, 10% dextrose
down to 45% fructose), salt, vanilla. How much of each? Who
knows. The salt and vanilla can probably be ignored because the
quantity would be very small. Oh, and by the way, don't bother trying
to get any information out of Karo or other manufacturers as to what the
quantities of ingredients are in their product. A number of us have
asked and they won't say. So though straight corn syrup is 93% to 96%
dextrose, which itself makes an excellent sugar propellant, it is impossible
to know what exactly is in any specific corn syrup product. That is
why a certain amount of experimentation will be required when using corn
syrup. In reality, the results probably will not vary much from one
corn syrup to another.
Corn syrup also contains water. It can be
dried commercially to form a crystalline substance. This should be
kept in mind when deriving formulas because that portion that is water adds
to the weight but does not contribute as a fuel. The formula for the
propellant when using corn syrup should have a higher percentage by weight
of corn syrup to account for the moisture in it.
I did an experiment to see if heating would drive off the water in the corn
syrup. I weighed a Pyrex container, added a weighed amount of corn
syrup, then put it in the oven
at 300 degrees. By the time it quit loosing weight four hours later,
the corn syrup had lost 20% of its weight so I conclude that Karo©
Light Corn Syrup is 20% water. This can also be derived by determining the specific weight and the grams/serving of carbohydrates (see
explanation below in "Corn Starch Content?"). A formula for
sucrose propellant that would use the
standard 65:35 ratio and split up the sugar half and half with corn syrup
would calculate like this:
Not accounting for the water in the corn syrup:
65% potassium nitrate
17.5% corn syrup
Accounting for the water in the corn syrup:
62.2% potassium nitrate
21% corn syrup
When the water is boiled off, these
initial percentages will end up with 65% KNO3 17.5% sucrose,
17.5% corn syrup without water, which is what you want.
Corn Starch Content?
It is interesting that when looking at the "nutrition facts" on the Karo©
Light Corn Syrup bottle I see the following: Serving size 2 Tbsp
(1/8 cup, 1 liquid oz), amount per serving: total carbohydrates 31g,
sugars 12g. I did some weighing and calculations and found that the
specific weight (weight compared to water) of the corn syrup is 1.37. One
ounce = 28.35 grams so one fluid ounce of corn syrup would weigh 28.35 *
1.37 = 38.8 grams. So if only 31 grams are carbohydrates, that means
only 79.9% is carbohydrate. That means the rest, or 20.1% is water --
almost exactly what I found when I drove off the water in the oven.
However, if only 12 grams are sugars, then what is the other 19 grams of
carbohydrates? What seems obvious to me is that it is corn starch.
Corn syrup is made by processing corn starch and they can stop at any point
they want to get whatever amount of conversion they want with some ratio of
corn starch and dextrose and a few other sugars in small amounts. It
appears to me that corn syrup (this brand) is probably the following:
49% corn starch
* The sugars would be a mixture of dextrose and fructose depending on what
type of high fructose corn syrup was in the mix and what percentage was
added to the light corn syrup. There is no way short of an organic
chemistry lab and chemist to find out what the sugar ratios are.
By comparison, Western Family© Light Corn Syrup Contains
only: corn syrup, water, potassium sorbate (preservative), vanilla and
citric acid. It contains no high fructose corn syrup. It still
has a similar ratio of total carbohydrate grams and sugar grams. The
serving size is twice as much, 1/4 cup. The specific weight is the
same but for that quantity, it has 61g carbohydrates and 21g sugar.
Since this is two fluid ounces, there is 28.35 * 1.37 * 2 = 77.7g total
leaving 16.7g of water. This corn syrup would figure out to be the
51.5% corn starch
* In this case, we could assume the "sugars" are primarily dextrose since
there is no high fructose corn syrup listed as an ingredient.. There
is about 4% less sugars in this corn syrup and just slightly more water but
the ratios look very similar.
If this is the case, that corn syrup has a large percentage of corn starch
in it, the effects become a bigger unknown and trying to figure out the best
formula mathematically becomes impossible. I experimented with a fuel
with corn starch, dextrose, and water in the same ratios as has been
calculated. The result was a mixture that would not sustain burning at
atmospheric pressure. It was worse than using corn syrup the same
I also am curious what effect corn starch has on the brittleness of cured
sugar propellant. Is it the corn starch that makes the propellant less
brittle, the water left in or the specific combination of compounds in the
corn syrup? Sucrose syrup will crystallize over time. Would
similar syrup made with dextrose crystallize over time or would it be like
corn syrup and not crystallize?
The only difference in the two is the Western Family, to my taste buds,
tastes slightly sweeter and is amber in color where the Karo is lighter with
less amber color.
James Yawn was probably the first to use corn syrup as an additive.
Others that also use it probably got the idea from his web site. The
corn syrup (such as Karo®) may decrease
the performance but only very slightly since it too is a mixture of sugars.
The decrease in performance will depend on the final ratio of sugars (fuel)
to KN (oxidizer). Actually, his formulas are fairly fuel rich and so
you should expect performance several percent below the optimal 64-36 (or
65-35) formula. Currently, you will find quite a number of ratio
variations on various pages of his web site. Here is one of his formulas:
10.7% light corn syrup
To this he adds 47.6 % water (figured as a percentage of the total of the
The numbers don't end up in whole percentages because I converted his
actual formula which is given in specific gram quantities and tablespoons of
water. Here is his specific formula:
18g light corn syrup
5 tablespoons water
His formula is used with his "recrystallization" method (a form of wet
mixing). The corn syrup makes the mix more pliable and workable for
his method. It remains soft at a lower temperature than without it.
I have tried this formula and it has merit.
In my own experiments with Jimmy's formulas, when I made it, it would barely burn when made into test strands.
(maybe I did something wrong). This is obviously at
atmospheric pressure and at operating pressures, it burns better but still,
in my tests,
below normal expected specific impulse values. I tried varying the ratios to more standard ratios
with better results myself. That being said, "the proof is in the
pudding" -- he has been flying these in rockets for a long time.
Dan Pollino and "Flexible" Sugar Propellant
"flexible" propellant is just a variation of Jimmy's propellant but he mixes
it differently. Where Jimmy's formulas are a little fuel rich, Dan's
"flexible" sugar propellant is a little oxidizer rich when you take into
account the amount of water in Corn syrup. His formula is:
65% Potassium Nitrate
15% Sucrose (Powdered Sugar)
19% Corn Syrup
His mixing method
is: First mix thoroughly the potassium nitrate (ground fine) and
powdered sugar. Next, heat up the Corn Syrup to 180°
F, then stir in the potassium nitrate and powdered sugar. Stir
constantly. When the mix is at 210 degrees, it is ready for casting.
It is interesting
that Dan's process never heats the propellant or components above 212, the
boiling point of water, so little of the water in his mix is driven off.
The effect could be similar to leaving some water in a standard formula.
I tried that in the process of my caramelization experiment. As would
be expected, it burned slower and the specific impulse was less.
However, when plugging the numbers from Dans K450 PVC rocket engine into
FPRED motor design software and using a straight 65/30 KNO3/sugar
fuel the total impulse was nearly identical to Dan's listed value.
Fuel behaves differently under operating pressures and there his fuel allows
a grain to case bond and be cast in one shot in a 24" long motor, it
doesn't crack as a large grain, and it has carried at least one of Dan's
rockets supersonic so as with Jimmy's, "the proof is in the pudding."
Glycerine has a similar affect as corn syrup but I think may reduce
performance a little more. The place I ran into it was on Dan Pollino's "Inverse Engineering" web site. He was using corn syrup in
his J300 (J size motor) but was having a problem with what is called
"chuffing" (oscillations in the thrust) and a pressure (and so thrust) spike
where he figured the propellant grain cracked. Richard Nakka suggested he
try glycerine in place of the corn syrup. That solved his problem.
Dan's formula is:
This works out to:
when you ignore the water which boils out anyway.
Richard Nakka experimented with a number of other ingredients as "burn rate
modifiers." Jimmy Yawn uses red iron oxide to increase the burn rate
and effectively uses it in a motor the same size as the standard A to C size
commercial black powder motors. It appears that red iron oxide
increases the burn rate somewhat uniformly at all pressures (increases the
burn rate coefficient) and with brown iron oxide the burn rate increases
more at higher pressures (increases the burn rate exponent). I am
currently (9-9-06) experimenting with iron oxides to make end burners. See
& End Burners.
Richard's experiments added 1% iron oxide. For example for 100 grams of
propellant, he added 1 gram of iron oxide.
A person could use other ingredients to slow the burn rate but this is
seldom a requirement and this could be done by increasing the nozzle throat
diameter and so decreasing the pressure and it would accomplish the same
There are a number of different methods for preparing sugar propellant but
the most variation is in the heating method. Other than the dry
compressed method which is not used by serious experimenters, all methods
require heating the propellant. The temperatures used range from
around 180° F to 400° F
This method is mentioned also on the general
propellant page. As stated above,
this method is not used by serious experimenters though it can be a novel
experiment to compare the repeatability and impulse to other methods.
The sugar and KN are ground as fine as possible and then mixed thoroughly in
a ball mill or tumbler of some kind to make sure the ingredients are mixed
completely and uniformly. This mixture is then compressed into the
motor tube in the same way as black powder is done. See the
1979 manual for details (pay attention to
Note: this paragraph is included here only for a complete coverage of all
methods. Dry heated or dissolved and heated methods should be used for
This is the most common method that has been used for caramel candy
propellant for decades and is still the preferred method by many. At
the writing of this, it is the method still used by Richard Nakka and other
well known people to the AER sugar propellant community.
The KN is ground or
milled to a fine powder if it is not already that way which it seldom is
unless it is a higher priced and higher quality such as lab grade or as
purchased from pvconly.com.
It should then be thoroughly mixed with powdered sugar. See a diagram
of Richard Nakka's mixer he made on
This mixture does not melt both the KN and sugar. KN melts at 631
degrees. What this method actually does is melt the sugar and then
with lots of stirring, it coats the KN grains with the melted sugar.
So the finer the KN is ground, the more intimate contact the sugar will have
with the KN and the better the propellant will be.
Just enough water is added to dissolve completely the KN and sugar.
Actually, you can use more and it doesn't take that much longer. I
heat the water first, then dissolve the KN and then add the sugar but it
doesn't really matter. You could do either first or both together.
The mixture is brought to a boil and the water quickly evaporates off.
it goes through several stages that are distinctive. First it boils
like boiling water, then as most of the water is driven off, it starts
bubbling and spitting. Then that stops and it just hisses a little.
At last it turns to a mashed potato consistency. The mixture should be
stirred a lot after the fist boiling stage. The more it is stirred,
the faster it comes up to temperature and reaches completion. The
temperature first stays around 212 until most of the water is driven off.
Once it gets to the hissing stage where the last of the water is being
driven off, the temperature starts to climb and you are getting close.
When it gets to around 350 degrees it is ready to cast.
In contrast to the dry heated method which coats the KN particles with
sugar, the dissolved and heated method actually dissolves both ingredients
which then mix intimately together. When the water is driven off, the
two stay in intimate contact and then as they cool, they both recrystallize
together providing a better mixture. In reality, if in the dry mix
method, the KN is ground to a fine talc-like powder and mixed very
before heating, the resulting grains will be comparable in performance.
Dissolving the sugar and KN in water first
and then heating the mixture has
The KN and sugar do not have to be
finely powdered. They both dissolve in water completely. You
don't have to use powdered sugar, you can use granulated sugar which is
cheaper and less messy. My KN was a 100 pound sack that sat for
years and turned into one solid chunk. All I have to do is chip off
small enough pieces to weigh and it dissolves in the water. If you
heat them dry, they must be finely powdered and thoroughly mixed before
You don't have to pre mix the
components. Once they are dissolved in water, they mix easily and
The mixture heats very rapidly and
thoroughly because it is in complete contact with the bottom of the
container and the heat is transferred efficiently through the mixture.
The mixture heats much, much more rapidly than dry ingredients. The
dry ingredients particles are not in intimate contact with each other
because there is air space between them. Air does not conduct heat
well. Imagine a jar full of marbles and all the air between them.
The same is true of the dry material but at a much smaller scale.
The finer it is ground, the better the contact but it is still
considerably less efficient than with water. Similar batches (250
grams) in my deep fryer took more than an hour to heat dry and only 20
minutes to heat to completion with water.
Lower temperature. Because of
the above effect, the dry mixture needs a higher temperature at the bottom
to transfer the heat through the mixture and this ends up causing the
whole mix to be at a higher temperature to get to the same consistency.
The dry heated method needs to be about 380 degrees. When the
mixture is heated dry, you have to get it hot enough to turn one of the
ingredients to liquid. KN has a very high melting temperature, 631°F, sucrose melts between 320°F and 367°F. So 380°F will melt the
sucrose and then the KN will dissolve into the liquid sucrose. Actually,
the sucrose isn't really liquid, it is more like putty and that is why
both must be finely ground and intimately mixed before heating. When
you dissolve the components in water, they are thoroughly mixed even
before they are heated or at least soon after. Then all you have to
do is drive off the water and what is left is good propellant. The
temperature is not critical, the higher the temperature, the faster the
water will be driven off, but a lower temperature works fine. To
start with, even 250°F is enough to boil the mix. The thermostat
causes the element to either be on or off so as long as the mixture is
below the thermostat set point, the element will be on. Until the
majority of the water is boiled off, the temperature will not go much
above 212°F anyway. Once the majority of the water is boiled off,
the temperature will start rising. Then it is just a matter of
bringing the temperature up to the point where the mixture is the least
viscous (thinnest) which will be 300°F to 350°F.
Longer pot life. Because the
mixture is ready quicker, you actually have longer to cast the mixture
into propellant grains than with the dry heated method. Caramelization will occur with either method but it is a function of
temperature and time. You have already used up a larger portion of
your pot life with the dry heat method simply because it has taken longer
to reach temperature and has actually already started to caramelize some
before it reaches that temperature. The higher temperature of the
dry mix method also decreases the pot life. The dry heat method also
requires a higher temperature on the bottom to get the temperature up on
the top of the mixture so this causes a quicker caramelization.
Less stirring. Although the
more you stir the mixture in either method, the faster it is ready, you
actually don't have to stir any where near as much with the dissolved
method. You can just let it cook until it is into the "blurping"
stage past the boiling stage before you start stirring it. With the
dry heat method, you have to stir it almost constantly and from the very
beginning. If you don't, it will just burn on the bottom before it
melts the top of the mix.
One possible negative to this method
is that the resultant propellant is a little thicker (more viscous).
It is not a pourable mixture no mater how you prepare it. It must be
scooped and packed either way, especially with smaller molds. The
more finely the sugar and KN are ground in the dry mix method, the thicker
the mixture. The dissolved method makes a thicker mix because you
really can't get a better and more thoroughly mixed propellant no matter
how fine they are ground in the dry heat method.
You may find various people claiming to
have come up with the method of using the dissolved method first but it
would be like claiming to be the first person to think of mixing up a cake
using a liquid as one or more of the ingredients. All you have to
do is be in a kitchen and the idea is so obvious as to be ridiculous not to
use water. If you took high school chemistry, you will also be very
familiar with dissolving chemicals in water to mix them and then driving off
Jimmy Yawn came up with a variation of
this and has been using his method for many years. You can see his
method on his website at
http://www.jamesyawn.com/rcandy/index.htm. His method is more
novel in his use of corn syrup and a kitchen oven to bake the liquid.
More recently, he has gone to the more common method of using a skillet or
Sorbitol -- dissolved and heated
method. Using sorbitol with this requires special methods and if
done improperly will result in a propellant that retains water and will
never cure properly nor burn properly. 500 grams of sorbitol
propellant will take over an hour to "cook" compared to 20 to 40 minutes for
sucrose. Scott Fintel uses 500 ml of water, 50 ml of distilled white
vinegar for pH balancing, 325 grams KNO3 and 175 grams of sorbitol. He
starts at 300 F and as it thickens, turns it down to 250 F, and finally to
200 F to finish it. The grains can then be cast and after casting
should be put in a desiccator for a couple days to remove any residual
A variety of method have been used to heat caramel candy propellant.
The concept of dissolving in water first is more important than the method
of heating. The main thing to consider when heating propellant is that
you don't want exposure it to a high temperature source or a flame so a kitchen
stove is not the best method. It is easy to spill a little propellant
and it will readily ignite on a kitchen burner. It also can splatter
during one phase of the preparation driving off the water. You don't
want an entire batch catching fire because there is no way to put it out.
It just has to finish burning and then the job is to put out what it caught
on fire. This is not even a remote option. You must use safety
procedures the prevents ANY possibility of this happening.
This is the least desirable method. If this is the way
it is going to be
done, it must be done outside away from all burnable material and using
protective clothing and a face shield (if you are smart). You must use
a double boiler.
A double boiler means that you have one pan that heats oil (any
kitchen oil like corn oil, safflower, etc.) or wax (paraffin which is what
candle wax is) and another pan that sits down inside the first pan.
The second must have a lip that extends over the lip of the first pan so
that it cannot go all the way down inside but is held up off the bottom of
the first. Many sets of kitchen pans include pans that can be used
this way. See additional details under the deep fryer section.
Jimmy Yawns original "recrystalized" propellant was done using a kitchen
oven for the last step. He dissolves his ingredients, heats them up to
boiling, then pours them into pie pans and puts them into the oven to
finish. It takes a lot longer and I see no advantage in using an oven
with a standard recipe for caramel candy propellant.
A Toaster Oven is even a worse choice. Because of its small size, the
temperature variation in it makes it very unreliable. I tried using
one and all I managed to do was burn it. You don't have access to stir
it and stirring is very important.
This is the second best choice. A used electric skillet or wok can
often be found very cheap at yard sales, estate sales, or thrift stores.
They actually aren't that expensive new. The advantage is that they
have a thermostat and you can control the temperature... sort of. Why
"sort of?" Any thermostatically controlled kitchen heating device (fry
pan, wok, deep fryer, etc.) control the heating element by just turning it
off or on. The thermostat probe is in contact with a portion of the
bottom of the pan and is actuated by the temperature of the metal in that
vicinity. The actual heating element is embedded into the bottom of
the pan and when the thermostat turns it on, it heats up. The portion
of the pan directly above the heating element gets hot. That heat has
to move out through the rest of the pan so it will be a lot higher
temperature at the element than it is at the thermostat probe location.
So what you have is a ring that alternately gets much hotter, then the rest
of the pan, and then cools in a cycling process. The actual variation
of temperature of the different areas of the pan is considerable.
Constant stirring of either the dry heat or dissolved heating method is
absolutely critical and even then, you will end up caramelizing some of the
mixture. In the early heating stages of the dissolved heating method,
it isn't important because the liquid will distribute the heat but as the
water is driven off, constant stirring is required.
Trying to use an electric skillet or wok in a double boiler arrangement is
not practical. You'll slop the oil or wax all over.
This is the best method. I use a double boiler arrangement with a deep
pan that sits down inside the deep fryer. I found a Presto deep fryer
at Kmart that was inexpensive and has worked excellently. Any double boiler
arrangement is a little more complex and a little more trouble because of
the extra heating fluid and extra pan, though, so using an electric frying
pan with constant stirring in the last stages may still be the most
The deep fryer has a similar heating arrangement as an electric fryer but
has the advantage of being deep and readily adaptable to a deep fryer
configuration. It can be used without the deep fryer arrangement in
the same way as the electric fry pan above and has the same requirements for
stirring and the same handicaps, plus being deeper. The advantage of the deep fryer
arrangement is that the wax or oil (wax is shown below and is what I use) is
in contact with the entire bottom and lower sides of the inner pan and so
the whole inner pan is at the same temperature. The wax or oil stays
at a constant temperature and so does the inner pan as a result.
Because it is all at the same temperature, you don't have the problem with
the propellant caramelizing or scorching over the element. You will
find that your propellant will not heat up to as high a temperature as what
the thermostat is set to, however. Because the propellant is
constantly loosing heat to the air as it is getting heat from the pan, there
will be a small temperature differential.
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