Qs re dishwasher v. lye

[maloney108]

Yair,

You are exactly right - my explanation is only a hypothesis and it's nowhere solid enough to put in an FAQ.  I'll keep searching the literature for answers, but I think this subject is too limited, too complex and unprofitable for anyone to have studied in depth.  

I am glad I got the discussion going, because your points about the seasoning being too dry to make the oil rancid are good ones to consider and Steve's comments about how it builds up so badly are very interesting too.  However, iron-fatty acid bonds (mettalo-organic) are similar to the ester bonds that make up fats (fatty acid esters of glycerol) and these are fairly weak.  Lye breaks these bonds easily.  I don't think the seasoning is completely polymerized, rather I think polymerization is one of many components of the process.  As I said, if it were only a polymer stuck to the nooks and crannies of the iron, then I think (another hypothesis based on some experience) it would deteriorate with repeated heating rather than improve.  Lye is very good at hydrolysis and not necesarily good at reacting with polymers unless they are polyesters (Come to think of it, if the fats do polymerize into polyesters, maybe we could recycle it into liesure suits!).

You are right about the salt being a simple abrasive, but Kosher salt is less crystalline and therefore much softer than table salt and the oil acts as a lubricant.  I never have a problem with removing any of my seasoning.

By the way, Steve, I like your style with the dishwashers - you'd have really clean drains too!

On a more serious note, I'd be careful putting aluminum in a dishwasher.  Try a cheap piece first.  Typical dishwasher detergent is a lot stranger than standard hand washing stuff and diswashers run a lot hotter too.  This might dull the aluminum, I've put some non-vintage aluminum stuff in there and it comes out with a cloudy surface.  Magnalite and other aluminum alloys might be more resistant, but I'd do a test run first.

This is a fun discussion - keep the comments coming!

Cheers,

Jim

[Mitzi]

Okay, Jim's got me pulling out my textbooks.  Jane, I share your interest also in the "mechanism for seasoning" and I hope what I found is helpful.  Jim, Marvin, CB, Yair, please try to make sense of these passages and explain them to me!

I found this information in a book Alton Brown often holds during his show, titled On Food and Cooking, The Science and Lore of the Kitchen by Harold McGee.  (Jean, A.B. IS a God!)

"...In order to forestall rusting, cooks try to build up an artificial protective layer on cast-iron pans by "seasoning" them, or coating them with cooking oil and heating them up for several hours.  The oil penetrates into the pores and fissures of the metal, sealing it from the attack of air and water.  There may also be an effect analogous to the behavior of the drying oils, which are largely unsaturated, prone to oxidation, and which polymerize to form a dry, hard layer when exposed to air.  Since both heat and metallic ions accelerate fat oxidation, it may be that a similar layer is produced during seasoning with cooking oils....atmospheric oxygen ...is one of the major causes of flavor deterioration - rancidity - in foods containing fats.  How this fat oxidation occurs is not fully known.  It is thought that the electron-hungry oxygen replaces the hydrogen on a carbon adjacent to the double bond, thereby forming a very unstable complex which decomposes and produces various other reactive compounds...(Jim, help)...the more unsaturated the fat, the more prone it is to this sort of deterioration...it turns out that the tendency for highly unsaturated fats to be quickly oxidized can be very useful.  The so-called drying oils - linseed oil is a common one - are used in paints and furniture polishes precisely for this quality.  These materials oxidize so rapidly and completely on contact with the air that they form a dry, hard, protective film of hydrocarbon polymers."

I

[Steve_Stephens]

Wow, MItzi,
Tying all that info together to come up with a simple explainaton isn't that simple.

One thing, though, that I have wondered about for a long time is if cast iron REALLY does have pores in it.  What if it's not ground?  Are any pores sealed over but little holes inside the iron?  If ground any holes in the iron would become pores.  

Steve

[Mitzi]

Jim, do you have access to a scanning electron microscope?

[Steve_Stephens]

Jim, do you have access to a scanning electron microscope?

I did a long search on google for 'pores cast iron' and scanning electron microscope iron' etc. but no luck on seeing what I want to see.  The first search for pores cast iron was all about cookware.  It could be an old wives tale that cast iron has pores but maybe it really does.  I'd love to see some SEM photos of both as-cast iron and ground iron to see what the pores look like.  I would think any pores COULD be small enough that the oils would not get into them.  

Steve

[maloney108]

Mitzi,

I'll have to work on that electron microscope!  

One thing to understand is that cast iron is crystalline - it is molten and turns into solid  metal by crystallizing.  Forged or rolled iron like stainless steel cookware undergoes some milling first and that changes the crystal structure a lot.  I do think the raw cast iron crystal structure is somewhat porous, but I think it's the coarseness of the crystal structure and greater surface area that is different in cast iron.  I'm sticking to my "bonding" theory, from my posts above.

I thought of something that might shed some light if someone wants to try it.  I've seen some talk about seasoning chromed pieces being difficult - you get the blotchy yellow stuff.  Maybe the roughness of bare cast iron avoids this, but I think maybe the chrome doesn't react the same as the iron.  Here's my idea:  chromed pieces were made by first polishing the iron very smooth, then plating.  Some old pieces have lost their some of the plating but still have the smooth iron surface.  Has anyone seasoned a piece like this?  If the smoothness makes the blotchy yellows, it should do the same thing on the chrome parts as well as the smooth iron.  If it's the difference in reactivity of the iron vs chrome , then the smooth iron should season differently than the smooth chrome parts.

[Mitzi]

Jim, I can't quite figure the seasoning component out.  It just amazes me that pans have been seasoned since the Iron Age 1200 years ago, and all of these chemical reactions have been taking place.  I read that cast iron is alloyed with about 3% carbon to harden the metal.  Could your bonding theory work with carbon bonding to the fat, and not just iron?  Oxidized fat and carbon sounds like...crud!

[maloney108]

Mitzi,

The carbon in cast iron is unlikely to bond to anything, but it might attract and hold the fatty (oily) part of the fatty acids. In gray cast iron (I think this is what our pans are made of), the carbon is in the form of microscopic bits of graphite and graphite is nearly inert under normal conditions.

On another point of chemistry, not all oxidation is bad, our bodies carefully oxidize fat to obtain energy from it, but in uncontrolled conditions, yes, oxidized fat and carbon = crud!   If you want to learn a little more about fats and fatty acids, check this out (it's not too technical):

                  http://www.supplementquality.com/news/fatty_acid_structure.html

I looked for some microscope pictures of cast iron, but I realized they won't do us much good, since the metal is usually prepped by highly polishing it and then chemically etching it.  

Finally, The more I think about it, the more I think that iron is not very porous, after all, it's a liquid when they pour it, not a bunch of particles that melt together.