Temperature and time?

[Donna Manion]

Is there a specific link concerning the temperature and time at that temperature CI needs for fats (I use Crisco) to polymerize?  I have read various opinions--less than smoke point, at smoke point, higher than smokepoint-- but haven't been able to find a definitive answer.  I have looked on this website and other CI sites, as well as trying papers written by scientists but have not been able to nail down the science of it.

(Yes, I've seen the smoke point chart.)

Can someone point me in the right direction?  Thanks!

  :o

[Duke Gilleland]

I preheat at 250 for 30 minutes then take out and apply solid Crisco. WIPE OFF AS MUCH AS YOU CAN and put in oven at 400 for about an hour. Allow to cool in oven.
This is what works for me and has for over 10 years [smiley=thumbsup.gif]

[Donna Manion]

Duke, thanks for your reply.  Can you point me to anything that delineates whether polymerizing happens below, at, or above smokepoint?  If you are using Crisco and are going to400, you must be in the "above smoke point camp."     :)

[Lewis Downey]

Donna,

I think you are asking a fine question!

I am interested to know if there is any solid research or even a well-documented theory of what happens when iron is seasoned. Better would be to find something that is written such that a layman has a shot at understanding it.

Perhaps your CI could be seasoned for a period of time below smoke point then heated above smoke point for a similar period of time.  If the critical bond happened below the smoke point I would be surprised to learn that heating the iron above the smoke point reverses it. If it happened above smoke point, sez me, why would any harm be done by heating it to the lower temp.

There are people in WAGS whose academic and professional background include quite a bit of chemistry. Maybe someone can help the rest of us clue into what is actually happening when iron is seasoned.

Anecdotally I have seasoned between 200 and 300 pieces of cookware. My best results seem to occur when the temp is significantly above smoke point for a minimum of an hour - often more than two hours. Can't prove it, but it seems to be so.

Crisco shortening is my primary oil. It gives good results and washes out of my cleaning cloths more readily than some other oils. Cooking sprays in particular seem to permanently embed into the fibers of the cleaning cloths. Some people use paper towels and would not have that issue. Maybe other people are better at laundry :).

People on this board (and Lodge Manufacturing!) say to use melted Crisco (which I do). In addition to the baking temp, I wonder if there is a best temp for the oil. Why wouldn't there be?  I do not know what temperature causes Crisco to liquefy but say that it liquefies by 200F and smokes around 325F. Is it better to apply the oil closer to 325F or 200F?

100+ pans ago I used grapeseed oil quite a bit. I started with an expensive bottle from Whole Foods and got pretty darn good results. Just as that bottle of oil was depleting I bought a 1/2 gallon-sized bottle of grapeseed oil in Costco at a lower cost than the small bottle. I had consistently bad results with it - mostly spots from imperfect removal of the oil during wipe-down/degreasing. The Costco oil seems more viscous than the other oil -- which leads me to wonder if the viscosity of the oil matters. Even if there are other quantifiable differences between the two bottles of grapeseed oil, I wonder in a general way if viscosity matters. I expect less viscous oil more readily overcomes surface tension and flows into tiny nooks and crannies better than more viscous oil. I speculate that less viscous oil is also easier to wipe off before baking. My working theory is that the most critical part of seasoning is degreasing the oiled pan - although baking time and temp are also critical.

Increasing the temperature of the oil lowers its viscosity. Less viscous oil seems easier to remove. Therefore, sez me again, Crisco that is applied at a higher temp is both more effective at coating uneven surfaces (for example the textured surface of modern iron) and easier to remove. Can't prove it.

I am tempted to go on with more questions about the seasoning process, but I'll slow down for the moment. I hope you are able to find a solid answer to your question and  share it with us!

Can't help it, more seasoning questions... say you could apply oil in two ways:
[olist]

• dunk the pan into a deep fryer then wipe off all of the oil except the thinnest possible layer.
• mete out a minimum of oil, coat the pan with it then degrease down to the same thin layer as the deep fryer method
[/olist]
Do you get identical results? Is one result better than the other?  Somewhat related: could you season a pan in a deep fryer? Somehow I doubt it, but why not? Lack of oxygen? If it worked, I think you would probably be seasoning below smoke point. Unrelated: prevailing wisdom seems to suggest that oil should be applied then left to set for a few minutes before being removed. I do that and it seems to give good results, but why?

Seasoning is mysterious.

[Jeff McGrady]

[size=12]Good questions....I am subscribed to the thread, look forward to reading more![/size]

[Jim Fuchs]

 Two things happen when you season...polymerization and carbonization. First oil is polymerized (sticks to the surface), then, after reaching above the smoke point, it carbonizes (turns dark). The polymer layer gives it the slick surface, the carbon the color. At least that's what I have read and experienced. We do have chemists, and perhaps they could shed something further.  I was an engineer (Mechanical), but not a Chemist.  :)

[Lewis Downey]

Jim, thank you!

What has to happen for the oil to polymerize? Can you (or anyone) help structure my model of that elemental reaction a little more?

My simplistic understanding of polymers from high school chemistry is that a polymer is a long chain of molecules. I am not quite making the connection between the oil poymerizing (forming a long molecular chain) and it sticking/bonding to the surface.

[Cheryl Watson]

I'll post some links as I find them:

http://nfscfaculty.tamu.edu/talcott/courses/FSTC605/Class%20Presentation%20Papers-2015/Frying%20Oils.pdf

http://www.expresspolymlett.com/articles/EPL-0004054_article.pdf

http://file.scirp.org/pdf/OJPChem_2015080615333698.pdf

http://onlinelibrary.wiley.com/doi/10.1111/j.1541-4337.2006.00009.x/pdf

https://naldc.nal.usda.gov/download/2552/PDF

Happy Reading.... :D

[Jim Fuchs]

    From the Science of Cooking...

[Lewis Downey]

Jim, that is fantastic. Very helpful. Thank you!

This sentence in the Science Of Cooking article begins to address my question about connecting the polymerization of the oil to bonding with the cast iron.

When an unsaturated fat is heated to high temperatures, especially in the presence of a good catalyst like iron, it is broken down and oxidized, after which it polymerizes –joins into larger mega molecules the same way plastics do – and mixes with bits of carbon and other impurities. This tough, impermeable surface adheres to the pores and crevices in the cast iron as it is forming.

It reads as though some of the carbon in the polymer chain comes from the cast iron. Can a carbon atom belong to both the polymerized oil and still remain part of the cast iron? I'm hoping the short answer to that question is 'yes'.

Apologies in advance if I'm being a noodge with this next question. Your previous post seems to suggest that the oil polymerizes below smoke point.

Two things happen when you season...polymerization and carbonization. First oil is polymerized (sticks to the surface), then, after reaching above the smoke point, it carbonizes (turns dark).

The Science Of Cooking article says

Low temperatures do not completely polymerize and break down oil and will leave a brown, somewhat sticky pan instead of a black, nonstick one. 400-500 degrees F is the effective range for seasoning.

Both could be true if the oil had a smoke point above 400°F, but according to the Good Eats article linked as a sticky on this forum that oil would not be Crisco™.  The Good Eats article lists "shortening" as having a smoke point of 325°F. Do you have other documentation about polymerization occurring below smoke point or did I cross-wire something along the way? You did not mention Crisco™ but lots of us us it, and it works beautifully.

[Cheryl Watson]

Ingredients of Crisco Shortening are:

SOYBEAN OIL, FULLY HYDROGENATED PALM OIL, PALM OIL, MONO AND DIGLYCERIDES, TBHQ AND CITRIC ACID (ANTIOXIDANTS).

I would cross check against the  smoke point charts for both Soybean Oil and Palm Oil.

The last reformulation of PAM added Palm Oil as an ingredient.

However, I have not been seasoning for using much since that occurred, however, I expected it would have a positive effect.

I have used high heat seasoning from the beginning (500°) and see no reason to change, regardless of the type of oil.  :)

[Jim Fuchs]

   Think this gets over analyzed at times.  An oil with enough saturated fat to carbonize, and enough unsaturated fat to polymerize is ideal ( so I have read) . What happens first, I am not sure, and don't get concerned about it at all.  Here's what I do...if I season...I clean the iron, and then I cook with it (being careful of sugar content). I don't season my iron for looks..(maybe one out of one-hundred-maybe).

[Mark R. Smith]

After the reformulation of both Crisco and Pam to include Palm oil I started looking for another oil to use since palm oil farming is not good for the environment. I also looked at what Lodge uses for their preseasoning. It is soy based vegetable oil. You can get soy based vegatable oil very cheap. It is GMO but I'm not eating it I'm seasoning with it. Also I looked at seasoning with Pam in the past that gives a great slick seasoning. Walmart sell their brand of cooking spray that is soy and the soy lecithin. It is really cheap compared to Pam. Works great. I do a couple of squirts on a pan at about 250 degrees. Then do the usual wipe it all over and then wipe it off. Crank up the heat to 450 and run for one to two hours depending let it cool and it is slick and dark. After use just one squirt to cooking surface wipe and heat on stove top till smokes. Every time it just gets better. Slicker than a non-stick.

[Donna Manion]

I really appreciate all the science that you guys have shared.  I have read so many anecdotes about different techniques on different websites, it's good to read some facts.  What I have gleaned from the posts here is that:

Polymerization may or may not happen above smoke point; I didn't read that was ever stated conclusively as below, at, or above smoke point.

Carbonization happens above smoke point. 

400-500 is the effective range for seasoning.

I wonder if laying down the layer of carbon is protective or merely attractive.  That wasn't addressed in the posted literature.

Thanks for everyone's input!

[Lewis Downey]

Donna,

There is a discussion on the ths.gardenweb.com site that is an especially good start for digging deeper into seasoning - at least it is for me. It happened about 10 years ago (2007).

A ex-marine/fig lover/retired chemist whose screen name is Danab_z9_la posted extensively in the comment section and responded to questions from other users. The comment section is what you want.


http://ths.gardenweb.com/discussions/2337724/cooking-with-cast-iron

Here are snippets from a couple of his comments in that thread:

March 7, 2007 at 5:17PM
...
Patina development on cast iron is a two part process. The first part involves developing a thin layer of polymerized oil on the cast iron. This is accomplished by applying a thin coat of oil to the cast iron surface and heating it in an oven until it dries to the surface. When done properly this layer of polymerized oil CANNOT be removed by either soap or dish washing liquid. The only way to removed this layer is by vigorous mechanical scrubbing (i.e. brillo pad), by caustics (lye, draino, or oven cleaner), or by burning it off at temperatures greater than 500 deg F (on BBQ pit or in Self Cleaning oven).

The second part to true Patina development on cast iron involves the actual lay down of carbon on the cast iron surface. This happens at temperatures slightly above the smoke point of the seasoning oil. You MUST heat cast iron above the smoke point to get actual carbon black into the patina matrix. If you do not heat to the smoke point you will only have polymerized oil in the coating........this is a protective coating but it is not as slick a surface as a mixture of both carbon and poly molecules.
...

March 24, 2007 at 2:05AM
Paul,
As I stated above patina development is a two part process. Part 1 involves the polymerization of the unsaturated oils/fats in the curing oil. Part 2 involves the thermal cracking of the oil/fat and actual carbon laydown into the matrix.

These two patina developing mechanisms can take place independently of each other or can occur almost at the same time........it just depends on the conditions at the time of the curing process. Factors affecting rates of patina development reactions include
[olist]

• concentration of unsaturated fats
• concentration of saturated fats
• temperature
• pressure
• pot metal metallurgy (catalyst affects)
• Conradson carbon residue content of the curing oil or fat.
[/olist]
It can get rather complicated (boring?) if I try to go into too many details. However, the seasoning process itself is not complicated at all if you follow good procedures. More on that later.........

Regarding Polymerization: Polymerization simply is a chemical reaction whereby molecules contained in unstable unsaturated (double bonded carbon atoms) oils or fats combine or crosslink with other molecules to form other more stable compounds with very different chemical and physical properties. Our goal in the curing process is to control these polymerization reactions in such a manner that they produce polymers with physical properties that are good for cooking purposes (i.e. a non-stick, hard, durable patina).

[olist]

• The rate of these polymerization reactions are very much dependent on type of oil, curing temperature, and the chemical composition of the metal surface.
• The chemical and physical properties of the polymer formed is also very much dependent on type of oil, temperature, and metal surface.
[/olist]
...

Over a period of months he invested close 7000 words in the comment section for that topic. Some of those words are just ordinary back-and-forth between users but there is a lot of good information in there too. It is the best discussion of the chemistry involved that I have seen and written such that a layman can understand or at least dig into it. There is enough information there to get a toehold for further research.

He posted comments on other gardenweb threads related to cast iron. Here are links to two. There may be more.

• http://ths.gardenweb.com/discussions/2423779/thanks-to-dcarch-danab-lou-and
  
• http://ths.gardenweb.com/discussions/2481844/cast-iron-question
  

Combining his comments for the three posts linked here, a couple of times he promises to post general procedures for seasoning CI. He sort of does at one point but not quite. Somewhere along the line he recommends only heating a little bit above the smokepoint of the oil being used. I did not notice any way to quantify 'a little bit'. He also kinda-seemingly contradicts himself whether to lay down the carbon first then polymerize or vice versa. I suspect that is the sort of process he planned to detail but did not get around posting.

[Jeff McGrady]

[size=12]Good stuff!![/size]

He also kinda-seemingly contradicts himself whether to lay down the carbon first then polymerize or vice versa. I suspect that is the sort of process he planned to detail but did not get around posting.

[size=12]This part is interesting, Lewis.
Jim already remarked about what occurs first, but I will echo:

One can definitely achieve polymerization without carbonization by using notably lower temps than is involved in the normal 'full seasoning' process.

My own experimentation has shown that I can begin to achieve polymerization---- depending upon the oil being used---- at oven temps of only around 225-250 degrees held over a period of as little as an hour.
(I have also played around with just heating a skillet treated with a thin, wiped layer of oil on the eye of my stove at only a range/dial setting of 4-5, and watched as the oil begin to polymerize.)

Not sure how such a thing might be useful, tho, unless one was simply wishing to cover an existing season that already had carbonization with an extra layer.....but the quality of that layer would be questionable, and why do that and not go on and heat to a higher level and achieve both a solid poly layer and carbonization (?)

Anyhow, I digress: Based on the chemistry/physics the guy over on gardenweb remarks upon, as well what I have seen evidenced with my own experimentation, polymerization has to occur prior to carbonization.

(To wit: I have an old gate-marked skillet that I stripped and ran through about 10 cycles in the oven, never going above about 350 degrees.....made for a strange looking skillet! It has a decent non-stick coating due to polymerization of the oil I was using (It was flaxseed....please don't throw that #14 Griswold at me, Cheryl !   ;)  ), but has no dark color to speak of: just slightly darker than the bare metal of the skillet after it was fully stripped.)
[/size]

[Lewis Downey]

Here is the unexpected part about laying down the carbon  before the polymerization. From a comment posted June 22, 2007 at 2:12AM on this gardenweb thread.

I'm having problems with Internet explorer on my computer and can't seem to get around a major freezing screen problem. For now here's a quick GENERAL procedure

Although I prefer lard, bacon grease or Crisco is fine. Your problem is: you're not heating your pans hot enough. You need to heat them UP TO the point of where you see them smoke.....don't heat too much past this point. Make sure you only have a LIGHT coating of oil on the pan.....no puddles allowed. Do this coating/baking multiple times until the pan is evenly coated with carbon black.

Then you need to bond it tightly together with the polymer reactions. You do this by coating the pan inside and out with VEGETABLE oil (preferable oil which was used to fry potatoes or fish). Apply a very THIN coating of oil and bake in the oven slightly BELOW the smoke point of the vegetable oil.......say around 450 degrees. Bake it until the coating feels dry and not sticky. Do this multiple times as well.......the more the better.

I'll try it to see what happens... a couple of bakes with Crisco (a few degrees above smoke point) followed by a couple of baking cycles just below the smoke point of a vegetable oil -- perhaps grapeseed oil.  According to Wikipedia Crisco was reformulated in 2007 and again by 2012. The author of the comments can be very specific. Maybe the reformulated Crisco is a no-go, but as a vegetarian I am not going to season with lard or bacon grease under any circumstance that comes to mind.

Polymerization may or may not happen above smoke point; I didn't read that was ever stated conclusively as below, at, or above smoke point.

Donna,  a piece of your inquiry seems to be addressed now. According others in this thread and the retired chemist who posted at gardenweb 10 years ago, polymerization does happen below smoke point. 

Another element of Donna's question is whether polymerization will happen above the smoke point. If the second part of the seasoning process is carbonization, which happens above smoke point, is it an either-or situation (either you're polymerizing or you're carbonizing) or can both happen simultaneously (above smoke point)?

Suppose you had a laboratory oven and could season *at* smoke point. Would you get polymerization, carbonization, both, neither? 

[Lewis Downey]

My own experimentation has shown that I can begin to achieve polymerization---- depending upon the oil being used---- at oven temps of only around 225-250 degrees held over a period of as little as an hour.

Jeff,

How do you know if you have achieved polymerization? I'm very curious as it sounds like a useful tool to have in the toolbox.

[Russell Ware]

How do you know if you have achieved polymerization?

Oil is liquid. If you can't wipe or wash it off after heating, and if it isn't gummy or sticky, I'd say it was polymerized. Depending on the heat setting of the oven and the smoking point of the oil, any excess would eventually carbonize if the heating continues.

[Jeff McGrady]

Jeff,

How do you know if you have achieved polymerization? I'm very curious as it sounds like a useful tool to have in the toolbox.

[size=12]Russell nailed it: once the oil is heated to a high enough temp, it begins to bond with the iron. It will no longer be a liquid and can no longer be 'wiped.'
Also agree with the 'sticky' remark, which would indicate a lack of full polymerization having been achieved, likely due to too low a temp, too short a bake, or both.

If you've ever coated your iron with a bit too much oil before heating, you'll note the little raised bubbles of polymerized oil which can no longer be wiped off, or which will take a good deal of elbow-grease to remove.

I've learned this the hard way, and have ended up having to re-strip items because I got into too great a rush and didn't keep the coating of oil thin/wiped well enough....  :-[ [/size]