Oil Amount and Measurements for Original KFC Pots
Nov 11, 2022 16:07:38 GMT
Ken_Griffiths, viper1431, and 1 more like this
Post by jwoz on Nov 11, 2022 16:07:38 GMT
I’ve made some interesting discoveries (or rediscoveries) about pressure cookers that I wanted to share.
Right up front I want to thank cascader for helping with this. His encouragement and help working through these details were the essential ingredients in pushing this forward.
Although I’m posting this mainly for posterity, this may also help some people currently.
This research involves the original KFC pressure cooker pots that were used by KFC restaurants before the “automatic” Collectramatic fryers were introduced. I have three of those original pots and I use them for my chicken experiments. However, I had never really analyzed them in detail. Once I did, a few interesting things were revealed.
I’ll give the two big findings right up front, then I’ll give some more detailed information.
First, the amount of oil that the patent says to use is almost certainly “wrong” insofar as it almost certainly doesn’t match the actual amount of oil that was used in the restaurants.
Second, although these pots are nominally called 16 quart pots, they really are 15 quart pots, by volume.
The “amount of oil” issue may have some relevance to how people are pressure cooking regardless of what type of pot they are using. The patent indicates that 7.5 to 8.0 quarts of oil are to be used for 5 pounds of chicken. This 8 quart number seemed off to me because when I used 8 quarts of oil with 5 pounds of chicken the pot was almost overflowing, and I couldn’t see how that would have worked in a restaurant environment. Therefore, I have almost always been using 7.5 quarts of oil, but I still wasn’t entirely happy with the temperatures that I was measuring.
To try to run this to ground, and at Cascader’s encouragement, I did a whole lot of measurements and a series of calculations. I also pulled out my original KFC thermometers that were used with the pots and measured the distance of the hash marks on them from the bottom of the pot (instructions with respect to these thermometers say that these hash marks have to be below the surface of the oil for an accurate temperature reading), I and looked at a bunch of pictures to try to figure out the actual oil level that was being used in the restaurants.
Cascader referenced that in the distant past swamprocker had indicated that he used 5.5 quarts of oil in his original KFC pot, but I hadn’t seen any other support for this amount.
One thing that kept bothering me, though, was a lack of understanding as to how these pots would have been filled to a specific level in the early restaurants.
We all know that KFC’s cooking process has gone through a whole lot of iterations.
To start with, in the very early days of KFC, it isn’t clear exactly how the cooks were getting the chicken out of the pots at the end of the cook. (Were they using slotted spoons, “spiders,” etc.?)
However, at some relatively early point, we know that KFC introduced “dump tables” where the contents of the pots would be dumped onto a wire rack, below which was an oil collector, like a funnel.
Then at some point there was an iteration of this concept where the oil would be kept warm and pumped back up into the pots which would be automatically filled to a certain pre-determined level. But before this auto-fill system was introduced, how would the cooks have known how much oil to put back into the pots after they dumped them? They couldn’t just have been eyeballing this. There had to be some kind of guide, but nobody has found any kind of measuring stick, measuring bucket or other container, etc., except for possibly the hash marks on the thermometers.
Well, without giving the entire blow by blow, when I closely examined the inside of two of my pots I found that an actual line was scribed in the aluminum. That has to be the fill line for the oil. This line appears at essentially the same place in both pots – an average of 7.275 mm from the bottom (there is a millimeter or so difference in the height of the line between the pots). When I did the math, and then when I measured the volume using water as a cross-check, I found that this line is at a level that would require 5.5 quarts of oil (really 5.6 quarts, but close enough). If I am able, I will post a picture of the line in one of my pots so you can see what I am talking about.
This line does not appear in my third pot, and this third pot is the pot that I have used for 90+% of my cooks, which is the only explanation I have for not noticing it sooner (but still, I am kicking myself). I don’t know why it doesn’t appear in my third pot, but possible explanations could be that it was polished out or that this third pot was produced only after the autofill system came into use, so the line marking wasn’t necessary.
In any event, I also confirmed that putting oil into the pots up to the fill line is more than sufficient to submerge the stem of my thermometers beyond their hash marks (which are in slightly different places on both thermometers, but the differences are minor), if the top of the thermometers were flush with the top of the pot.
On this basis, I think that these pots were generally used with approx.. 5.5 quarts of oil, which would weigh about 10.57 pounds. In contrast, the 7.5 quarts of oil I have been using weighs close to 14.5 pounds, which is a lot heavier (38% heavier).
Using 5.5 quarts – 10.57 pounds – of oil to cook 5 pounds of chicken gives us a clear ratio of right at 2 pounds of oil for every 1 pound of chicken.
Using this much less oil will definitely affect the temperature gradient of the oil during the cook, and could have a significant effect on the recipe’s aroma and flavor. This lesser amount of oil will cause the temperature of the oil to fall more quickly, so the chicken will spend less time at higher temperatures, and it is likely that the oil will spend more time at 250F than previously. But how dramatic the effect will be on the finished product will remain unknown until I cook some batches using this “new” oil amount.
This information could be useful to others in figuring out how much oil to use, although the thermal characteristics of various pots, pressure, etc., will certainly vary.
The best information regarding cooking times using these pots is that once the chicken goes in and the pots are capped, then the cooking time is 8 minutes before uncapping. This is the majority position and it generally comports with the offset hands on most of the three handed clocks that were used in the restaurants to time the cooking process, but it doesn’t actually comport with the three handed clock I have (which is set at 11 minutes) or a few others that I have seen which contemplate a longer cooking time. There are possible explanations for this that I won’t get into here.
Now, on to the volume of the pots.
Here are the basic measurements: Diameter, 12 inches, Radius, 6 inches, Height, 7.7 inches (30.48cm, 15.24cm, 19.558cm, respectively).
If you calculate the volume of the pot from these measurements you get 15.08 quarts. I was expecting 16 quarts, so to confirm the calculated result I also measured the volume using water, and when adding the 60th cup of water (15 quarts) the water was up to the rim and starting to overflow. So, although these pots are nominally “16 quarts” they really only hold 15 quarts of liquid.
Why? I don’t know. Maybe that’s the way that all of the “Mirro” 16 quart pots were built, or maybe these pots were tweaked for KFC. These pots are very big and heavy. The walls of the pots are 4.0mm thick with respect to two of them, and 4.4mm thick with respect to the third. One theory would be that because these pots were used in a commercial setting perhaps they were made with somewhat thicker walls, thus reducing the interior volume. But we wouldn’t know that for sure unless we also tested a non-KFC Mirro 16 quart pressure cooker from that era. (One other measurement for anyone who may care about this in the future – I measured the circumference of the pots as 39.175 inches (99.5cm)).
Finally, one interesting thing about the pots that I’ll point out is that the sidewalls are black from use, but there are bands at both the bottom and top of the inside of the pot that remain silver. This is hard to explain in words so I’ll try to post a picture in a separate post (since there is a limit of one picture per post).
At the bottom of the pot, under the level of the oil, the black starts at about 6.7cm from the bottom. As mentioned above, the fill line for the oil is at about 7.275 cm, so the black starts at a level that is about 0.5 cm below the oil fill line.
At the top of the pot, the width of the silver band is about 3.25 cm.
It might be interesting to consider what turned the sidewalls of the aluminum pot black, and to also consider that the culprit can’t simply be “the oil” since there is a significant area at the very bottom of the pot that is always in contact with the oil and that remains silver.
Here are some links to pictures and documents that people may find interesting (courtesy of Cascader):
Picture of and information regarding the “autofill” system that was used with the pots, including a picture of the pots in use and the associated oil level:
www.flickr.com/photos/craptoy/26673502812/in/album-72157664773065445/
Flickr album that, if you click through it, will show pictures of the pots, thermometers, the “three handed clock (with an offset of 8 minutes), and other equipment used by early KFC.
www.flickr.com/photos/craptoy/27363828140/in/album-72157664773065445/
Right up front I want to thank cascader for helping with this. His encouragement and help working through these details were the essential ingredients in pushing this forward.
Although I’m posting this mainly for posterity, this may also help some people currently.
This research involves the original KFC pressure cooker pots that were used by KFC restaurants before the “automatic” Collectramatic fryers were introduced. I have three of those original pots and I use them for my chicken experiments. However, I had never really analyzed them in detail. Once I did, a few interesting things were revealed.
I’ll give the two big findings right up front, then I’ll give some more detailed information.
First, the amount of oil that the patent says to use is almost certainly “wrong” insofar as it almost certainly doesn’t match the actual amount of oil that was used in the restaurants.
Second, although these pots are nominally called 16 quart pots, they really are 15 quart pots, by volume.
The “amount of oil” issue may have some relevance to how people are pressure cooking regardless of what type of pot they are using. The patent indicates that 7.5 to 8.0 quarts of oil are to be used for 5 pounds of chicken. This 8 quart number seemed off to me because when I used 8 quarts of oil with 5 pounds of chicken the pot was almost overflowing, and I couldn’t see how that would have worked in a restaurant environment. Therefore, I have almost always been using 7.5 quarts of oil, but I still wasn’t entirely happy with the temperatures that I was measuring.
To try to run this to ground, and at Cascader’s encouragement, I did a whole lot of measurements and a series of calculations. I also pulled out my original KFC thermometers that were used with the pots and measured the distance of the hash marks on them from the bottom of the pot (instructions with respect to these thermometers say that these hash marks have to be below the surface of the oil for an accurate temperature reading), I and looked at a bunch of pictures to try to figure out the actual oil level that was being used in the restaurants.
Cascader referenced that in the distant past swamprocker had indicated that he used 5.5 quarts of oil in his original KFC pot, but I hadn’t seen any other support for this amount.
One thing that kept bothering me, though, was a lack of understanding as to how these pots would have been filled to a specific level in the early restaurants.
We all know that KFC’s cooking process has gone through a whole lot of iterations.
To start with, in the very early days of KFC, it isn’t clear exactly how the cooks were getting the chicken out of the pots at the end of the cook. (Were they using slotted spoons, “spiders,” etc.?)
However, at some relatively early point, we know that KFC introduced “dump tables” where the contents of the pots would be dumped onto a wire rack, below which was an oil collector, like a funnel.
Then at some point there was an iteration of this concept where the oil would be kept warm and pumped back up into the pots which would be automatically filled to a certain pre-determined level. But before this auto-fill system was introduced, how would the cooks have known how much oil to put back into the pots after they dumped them? They couldn’t just have been eyeballing this. There had to be some kind of guide, but nobody has found any kind of measuring stick, measuring bucket or other container, etc., except for possibly the hash marks on the thermometers.
Well, without giving the entire blow by blow, when I closely examined the inside of two of my pots I found that an actual line was scribed in the aluminum. That has to be the fill line for the oil. This line appears at essentially the same place in both pots – an average of 7.275 mm from the bottom (there is a millimeter or so difference in the height of the line between the pots). When I did the math, and then when I measured the volume using water as a cross-check, I found that this line is at a level that would require 5.5 quarts of oil (really 5.6 quarts, but close enough). If I am able, I will post a picture of the line in one of my pots so you can see what I am talking about.
This line does not appear in my third pot, and this third pot is the pot that I have used for 90+% of my cooks, which is the only explanation I have for not noticing it sooner (but still, I am kicking myself). I don’t know why it doesn’t appear in my third pot, but possible explanations could be that it was polished out or that this third pot was produced only after the autofill system came into use, so the line marking wasn’t necessary.
In any event, I also confirmed that putting oil into the pots up to the fill line is more than sufficient to submerge the stem of my thermometers beyond their hash marks (which are in slightly different places on both thermometers, but the differences are minor), if the top of the thermometers were flush with the top of the pot.
On this basis, I think that these pots were generally used with approx.. 5.5 quarts of oil, which would weigh about 10.57 pounds. In contrast, the 7.5 quarts of oil I have been using weighs close to 14.5 pounds, which is a lot heavier (38% heavier).
Using 5.5 quarts – 10.57 pounds – of oil to cook 5 pounds of chicken gives us a clear ratio of right at 2 pounds of oil for every 1 pound of chicken.
Using this much less oil will definitely affect the temperature gradient of the oil during the cook, and could have a significant effect on the recipe’s aroma and flavor. This lesser amount of oil will cause the temperature of the oil to fall more quickly, so the chicken will spend less time at higher temperatures, and it is likely that the oil will spend more time at 250F than previously. But how dramatic the effect will be on the finished product will remain unknown until I cook some batches using this “new” oil amount.
This information could be useful to others in figuring out how much oil to use, although the thermal characteristics of various pots, pressure, etc., will certainly vary.
The best information regarding cooking times using these pots is that once the chicken goes in and the pots are capped, then the cooking time is 8 minutes before uncapping. This is the majority position and it generally comports with the offset hands on most of the three handed clocks that were used in the restaurants to time the cooking process, but it doesn’t actually comport with the three handed clock I have (which is set at 11 minutes) or a few others that I have seen which contemplate a longer cooking time. There are possible explanations for this that I won’t get into here.
Now, on to the volume of the pots.
Here are the basic measurements: Diameter, 12 inches, Radius, 6 inches, Height, 7.7 inches (30.48cm, 15.24cm, 19.558cm, respectively).
If you calculate the volume of the pot from these measurements you get 15.08 quarts. I was expecting 16 quarts, so to confirm the calculated result I also measured the volume using water, and when adding the 60th cup of water (15 quarts) the water was up to the rim and starting to overflow. So, although these pots are nominally “16 quarts” they really only hold 15 quarts of liquid.
Why? I don’t know. Maybe that’s the way that all of the “Mirro” 16 quart pots were built, or maybe these pots were tweaked for KFC. These pots are very big and heavy. The walls of the pots are 4.0mm thick with respect to two of them, and 4.4mm thick with respect to the third. One theory would be that because these pots were used in a commercial setting perhaps they were made with somewhat thicker walls, thus reducing the interior volume. But we wouldn’t know that for sure unless we also tested a non-KFC Mirro 16 quart pressure cooker from that era. (One other measurement for anyone who may care about this in the future – I measured the circumference of the pots as 39.175 inches (99.5cm)).
Finally, one interesting thing about the pots that I’ll point out is that the sidewalls are black from use, but there are bands at both the bottom and top of the inside of the pot that remain silver. This is hard to explain in words so I’ll try to post a picture in a separate post (since there is a limit of one picture per post).
At the bottom of the pot, under the level of the oil, the black starts at about 6.7cm from the bottom. As mentioned above, the fill line for the oil is at about 7.275 cm, so the black starts at a level that is about 0.5 cm below the oil fill line.
At the top of the pot, the width of the silver band is about 3.25 cm.
It might be interesting to consider what turned the sidewalls of the aluminum pot black, and to also consider that the culprit can’t simply be “the oil” since there is a significant area at the very bottom of the pot that is always in contact with the oil and that remains silver.
Here are some links to pictures and documents that people may find interesting (courtesy of Cascader):
Picture of and information regarding the “autofill” system that was used with the pots, including a picture of the pots in use and the associated oil level:
www.flickr.com/photos/craptoy/26673502812/in/album-72157664773065445/
Flickr album that, if you click through it, will show pictures of the pots, thermometers, the “three handed clock (with an offset of 8 minutes), and other equipment used by early KFC.
www.flickr.com/photos/craptoy/27363828140/in/album-72157664773065445/
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