Cleaning and Seasoning New and Used Cast Iron

Cleaning and Seasoning New and Used Cast Iron

written by Glen Carman
and posted with approval

Get a group of people who use cast iron cookware together and bring up the subject of cleaning and it’s a good way to get a real lively discussion going.   It seems everyone has their own idea about it, most times they will work fine, and this is not to disagree with anyone, but to put out some facts and get rid of some myths and more important to give the new person some ideas.

We have two main types of cast iron cookware to get ready for cooking with, new cast iron which can be pre-seasoned or not, and cast iron that may be is new to you but has been used by someone.   Also we have the subject of what fat/oil to use in the seasoning that needs discussed.  I will start this section on the oils and fats used to season cast iron.   The best definition of fats and oils are that oils are liquid at room temperature (normally considered 68F-72F) fats are solid or semi-solid at that temperature.

The other terms that comes up on fats and oils is drying oil, semi-drying oil and non-drying oil, the best way to understand this is to think oil paints, a drying oil will oxidize and form a tough dry film, like paint, in fact oil paints use drying oils and will harden solid after a short time, examples are linseed oil (flax oil) and Tung oil, these sometimes have chemicals called driers added to speed up drying, but they will dry out on their own and are mostly useful for wood finishes and despite more modern types of paint, they are still used to make paint as well as other uses.

Semi-drying oils will oxidize enough to get gummy (if dryers are added they can be used to make paint) and can cause problems with cast iron cookware if used to wipe an oven after use to prevent rusting.   Common examples of these are Canola oil and soybean oil, both commonly used in kitchens and often the cause of gummy cast iron that has been stored for a period of time.

Non-drying oils are oils that do not oxidize with exposure to air; good examples are olive oil, coconut oil and animal fats such as lard.   These will not turn gummy with time, although animal fats such as lard can get rancid after a time, these are not good for long term storage.   The more unsaturated fatty acids in an oil, the more drying factor it has, it is measured by what is called Iodine Value, this is how many grams of Iodine will absorb, the higher the value the better the drying factor of the oil is.

Iodine values of oils over 130 are considered drying oils and a couple common ones are:

Tung Oil at around 165-175

Linseed oil at 135-180

These are true drying oils in their natural state, although Tung oil is not used in cooking, linseed oil is, but under its other name, Flax Seed Oil.  Other common oils ride the line on if they are drying oils or semi-drying oils, depending on the particular lot of oil,  a value of 115 to 130 are considered semi-drying oils,  these can include:

Sunflower at 125-145

Grape seed at 125-145

Walnut at 120-140

Soy Bean at 120-135

Wheat Germ Oil at 115-135

Canola Oil at 110-130

Corn Oil at 110-130

Non-drying oil is one with an iodine value below 115:

Cotton Seed at 100-115

Rice Bran Oil at 100-110

Olive Oil at 80-90

Lard at 60-70

Beef Tallow at 50-60

Palm Oil at 45-60

Palm Kernel Oil at 15-20

Coconut Oil at 5-15

(Values are based on several sources and averaged.)

(Palm Oil and Palm Kernel Oil are different oils from different palms)

Any oil will work fine for seasoning with a new or stripped oven; the true seasoning involves carbonizing the oils to form a strong but thin protective layer over the bare cast iron, this keeps the food from sticking, it works like the Teflon on a Teflon pan, but just gets better with use instead of deteriorating and if damaged can be fixed.

The problem often lies when a piece is used and when dry oil is wiped on it to stop rusting, a drying or semi-drying oil will get gummy in time, the time factor is based on the iodine value.

I have always preferred olive oil for wiping a piece that will be stored over a couple of weeks, just a thin layer put on with a rag works well, for short term I often use lard, this is one pieces that get used often, my most used kitchen pieces and my camp ovens when cleaning up to go home from a trip.  Then for storage I clean them up and use olive oil on them.

We can see that the 3 oils from the palm family (coconut is a palm) have a lower Iodine value, I can’t remember ever seeing palm oil or palm kernel oil other than on ingredients on things like chips, the coconut oil has the lowest value but the cost is very high and the olive oil always comes in under the wire as a non-drying oil.

No matter how the cast iron was cleaned, a thin coating of oil and the oven being heated for a period of time is the way to season it, the times and the temperatures vary with who ever is telling how, I long ago concluded that any where from a ½ hour on up and at 300F to 400F will work fine, I often just grease it up with lard and bake bread in it, it seems to work fine for me and I don’t waste heat on an empty oven.

With that information out there we will now get to how to prepare the cast iron cookware for use, I will cover all three types separately.

The simplest is the new and pre-seasoned, most new cast iron is sold this way, although it says pre-seasoned; it still could use a little work.  I just wash it with soapy water and start cooking with it, I avoid any acid foods till the seasoning gets built up a little better, in fact I fine the best thing to do is simply coat it with lard and bake bread in it the first time or for a couple times, as long as you are careful and don’t burn the bottom of the bread a simple wipe with a towel will clean it without disturbing the seasoning building up.

New but not pre-seasoned will have some sort of oil or wax to prevent it from rusting, often these can be removed with just soap and water, the simplest way is to try this first and dry the piece with heat and see if you truly have bare iron or if you need to do more, if so then just proceed as if dealing with used cast iron as follows.

Used cast iron often causes the most controversy as to how to get it ready for use, many say if the piece looks good and is well seasoned just use it, I don’t, I prefer to strip it and re-season it, others may not, it’s just what I prefer.

As for the method used, it’s like the old saying, “and that is when the fight began.”   There are several methods; all will work if they are used properly, they all can cause trouble if used improperly, and the methods I know of can be heat, chemical, mechanical, electrolysis or even a combination of all of them.

The one I like in most cases is heat, although when it is discussed it seems to be the most controversial method with many saying you will ruin the piece, well you can, over heat it and/or heat it very unevenly and you can warp it, you can crack it or form an oxide layer often called red scale that makes it hard to season (the red scale can be removed by mechanical methods because it’s just on the surface).    Use heat in a sensible manner and there is no problem, but I will add this disclaimer I would hesitate using it on a really old valuable piece for two reasons, one is if you do over heat it and warp or crack it, then that piece is lost forever because they are no longer made.

The other reason is depending on when it was made, the metallurgy of it is not the same as modern pieces, most made in the at least last 70 or so years are not really true cast iron as in what comes from the foundry right out of the blast furnace that is called pig iron, most are or at least Lodge is cast out of 75% pig iron and 25% scrap steel, this lowers the carbon content, making it less brittle and allowing to molten metal to flow easier in the moulds, meaning there is less chance of a hidden flaw in the metal.   In fact very little today made of cast iron is true pig iron, it is further refined by adding other metal to it (mostly scrap steel) to make a better product and the whole science of that is beyond what we need here.

Before using any of the methods, I like to clean it with dish soap and water to remove any fats and oils, the heat method will smoke less that way and it makes the other methods easier because there is less to remove.

As for cleaning it with heat, I most often just take the piece or pieces with me to one of my camps and in the evening when the cooking is done (and before it gets dark, the time people want to sit around the fire) I just let the fire burn down to low coals spread out evenly and place the piece or pieces on top of the coals and let the crud burn off, removing it when clean and before the piece gets that red glow to it.   I then set the piece aside to cool then take it home and finish it most times.

Others use a self-cleaning oven, very simple and easy, it might smoke the house up some, I have used it in the past but no longer have that type of stove.   Others use a outside gas grill and that keeps the smoke out of the house, no matter what the method of providing heat, the goal is to clean it only and by not turning it red hot or beyond and heating it evenly it has worked fine for me for a lot of years.   After it has cooled, I put it in the sink (or if too big for the sink I use our bath tub) and use warm water and dish soap on it and scrub it up well removing all the burnt material with a stainless steel pot scrubber, others just oil it, and heat it, (more on this after the rest of the methods) to season it.

Heat done right has the advantage of removing all the build up, oils and often all or most of the rust.

Chemical methods most often involve either an alkaline substance or an acid substance to remove rust and built up layers, the alkaline substance most often being lye, (sodium hydroxide or potassium hydroxide solution) it is often used in drain cleaners and oven cleaners, and it is caustic so some care has to be used with it.  One method often used is to simply buy spray on oven cleaner and to use it on the piece than put it in a garbage bag for several hours, then remove and rinse.

When using the acid method one of three acids are used, one being acetic acid the acid found in vinegar, citric acid found in citric fruits as well as molasses and phosphoric acid, which is often used as metal prep for cleaning new metal before painting, but is also used in soda pop to give it that bite, Coca Cola having what is said to be the highest recent.

Vinegar can be used straight or diluted, and any type can be used, I use white vinegar because most times it’s cheaper and I use the store brand.  Most vinegar is about 5% acidity so go with the cheapest.

I use the vinegar for cleaning ovens that have gotten a bit of rust in them and I just use it for the inside, I just put a cup or so in each oven, I do use a little squirt of Dawn dish washing soap and fill it with hot water, I let it soak a half hour or so and then scrub it with a stainless steel pot scrubber, this has always worked for me, I’ve never used it on heavy rust, I prefer to clean it with heat first and then use this if any rust remains.

The method recommended by many for a vinegar bath is a non-metal container big enough for the piece or pieces and fill it with ½ vinegar/1/2 water and submerge the piece in and let it soak.   Most suggest not letting it soak to long, the time period varies from a ½ hour to 24 hours or the acetic will start to dissolve the pan and pit it.  I’ve let pans soak a couple of days and never saw this, but I generally don’t use as strong a solution.  I will recommend checking it from time to time to be sure.

The citric acid method seems to most often use molasses as a cheap source of this acid, the recommended amount being 1 part molasses to 9 parts water, this method is said to take 2-4 weeks by those who use it and the animal supplement type found at farm stores is the cheapest.

The phosphoric acid is perhaps best used as Coca-Cola I have used this in the past as a cleaner for small steel and iron parts, having also used the higher strength metal prep in the past; I don’t recommend it for home use.  The Coca-Cola works well to remove rust but making a vinegar bath although perhaps slower is cheaper than the Coca-Cola by far.

Acids do a good job of removing the rust and the built up old seasoning.

The lye method involves adding 1 pound of lye to 5 gallons of water (make sure the lye is added to the water and not the water to the lye) and soaking the cast iron in this, the cast iron can stay in it a long period with out harm.   One must remember lye is caustic and one must keep it from contacting the skin and is best done in an area where children and pets can’t come in contact with it.

Lye does a good job of removing the old build up, but is not that good for removing rust, many recommend neutralizing the lye with vinegar after cleaning, but rinsing well should remove all the lye, one can do this to make yourself feel good, if there is lye left, there will be a bit of bubbling when the vinegar is added from the Carbon dioxide being formed as the lye is neutralized.

Mechanical can be as simple as a good scrub pad, sand paper, steel wool or other similar items, or it can involve using compressed air to force an abrasive material under pressure, this is called blasting, the abrasive can bee sand, steel shot, ground corn cobs or walnut shell or baking soda.   The baking soda uses the finest grit and is what I recommend if having pieces blasted.  The other can leave a very rough surface, depending on the coarseness of the grit, the pressure it’s blasted at and when it comes right down to it the operator using the equipment.   Soda blasting is used for a lot of delicate restoration work so it will be fine on cast iron although it will cost more than the do it yourself methods.

The mechanical means can do a good job with build up and rust, but other than the soda blasting do involve some hard work, the soda blasting although I have never really checked prices is expensive do to the hourly rate of shop labor and materials.

The electrolysis method uses an electrical currant to remove the rust, it is a process similar to plating with chrome or other metals, but the process is reversed.   The iron from the rust is deposited on another iron rod rather than the metal from a rod being deposited on the piece as in plating; in fact this method is used in restoration work to remove plating before prepping and replating.

The rusty iron and the so called sacrificial rod are immersed in a solution of washing soda (Sodium carbonate) available at most any grocery store along with the laundry detergent at a ratio of 1-2 tablespoons per gallon of water.  The sacrificial rod and the cast iron piece are hung in a non-metallic container so they are fully immersed.   A manual (not automatic) battery charger is hooked up with the negative (black) to the piece to be cleaned and the positive (red) to the sacrificial rod and the current turned on, the rust them flows to the sacrificial rod and the whole process only takes a few hours.   A battery can be added to the circuit if the battery charger is not a manual one, the current to the tank needs to come from the battery and the battery charge keeps the battery from being drained.

I have at this point not tried this method, I may in the future, what I have written is a simple description of the process, I recommend anyone wanting to try it do a internet search and look at several sites that tell how to do it and also look at the pictures of the set-ups.

This is a good method, but it does have a higher set up cost than the other “do it at home” methods.

As I have always thought, there is no one best method, in fact sometimes cleaning up and preparing cast iron for use can involve more than one method, I offer this as a basic guide to the different methods, the choice of which ones to use and which works better for your situation I leave up to you.   This should give one a good idea of why things don’t always work out the way you want.

Cleaning and Maintaining Seasoned Cast Iron

Once the cast iron is seasoned and is used to cook with, we come to having to properly clean it, this is another place where the methods differ between people, I have seen long internet discussions on this that have almost turned hostile.  I have no real specific method or rather I should say I do the minimum I have to clean it, this will depend on what was cooked in it and once in a while I still burn something in it that makes a mess.

Sometimes, a simple wiping with a dry towel is good enough, other times a little water and a dish rag is good enough, if things are a little stuck a light rubbing with a stainless steel pot scrubber is needed, sometimes some warm water and a bit of Dawn are added, the piece cleaned, rinsed and dried, I sometimes put water in the piece, put it on the fire and boil it to loosen things, I’m even known to use a bit of Dawn then also, if need be, when boiling it, adding Dawn and the pot scrubber come into play, then things have really went wrong and it has happened a few times over the years.   Some of this goes against what a lot of people think or more likely what they have been told, but this is what I have been doing for years and I have yet to ruin a piece of cast iron.

One of the biggest problems is people do not seem to know the difference between the “seasoning” and the oils/fats wiped on to protect the piece from rust.    The seasoning it the carbonized oils that form the surface between the bare cast iron and the foods, this keeps the food from sticking to the bare cast iron.   This layer is actually very tough and can be hard to remove once it is well established.    What are not hard to remove is any oils that are on the surface of the seasoning, these may have been put on to preserve the piece from rust or it may be left over from cooking (more on this later).

If you look at a piece of cast iron that is bare metal, (such as a new but not pre-seasoned one) it is grey, light silver grey.  Now look at a well seasoned and oiled piece, it is black from the carbon.  Now lets say I just made chili (an acid food)  in one and then cleaned it with dish soap, then dried it on the stove, yeah it’s got a funny dry look, till I grab a rag, put a little olive oil in it and wipe it down, then it’s black again, not that silver grey of a new piece, our seasoning is still there, we have just removed the protective oils, as long as we wipe it down after cleaning with an oil there is nothing damaged.

I see all the time not to use the stainless steel pot scrubbers because something that rough will remove the seasoning,  it can if you get down and work it very hard for a while, but when needing a little extra, do you need to work it hard enough to remove the seasoning?   Few people when getting a new/used piece that they want to re-season will grab a scrub pad and some water and just strip it down to bare metal in a few minutes, one can do it but it takes quite a while and any food stuck on will be gone before you remove the seasoning.   The worst cases is burning something sugary and having a big carbon mess in the bottom then you have to scrub it that hard to remove, but it has to be removed and pretty much any method used will require some re-seasoning.

The one that strikes fear in so many people is the mention of dish washing liquid, aka soap in many people’s minds.   Well the Dawn I use is not soap but a detergent and a very mild on at that, they use it to clean wild life after an oil spill, so it is mild.  I’m know to point that out when people state you should never use soap on cast iron cookware, I ask them “what about detergent?”   The typical answer is “they are the same” which is not true, soap is a fatty acid treated with an alkaline substance, detergents are more complicated compounds that are one several types, that do the same job as simple soaps.  Both are surfactants which simply mean they make water flow easier; water that flows easier cleans better, allowing it to remove dirt and grease easier.   The big difference is that detergents work better in “hard” water, (water that has dissolved minerals in it) than soap does, which has caused it to replace soap for washing clothes and dishes in most cases.

Now that we know what they are, then why or why not use them on cast iron cookware?  Well the some tell us they will remove the seasoning, but the seasoning is carbonized oils and as most have found are very hard to remove when we want to start over, a little soap/detergent will not remove the seasoning, it may thin it slightly, but we put it on in the first place we can build it back up if need be.

As an experiment a year or so back, I took my Lodge round griddle I use for pancakes and pancakes only that is right at 20 years old.  I bought it new and it had never been washes, just wiped with a dry paper towel and put away.   I put it in the sink in the morning while I was having my coffee, put in about a ¼ cup of Dawn and filled the sink with hot water.  I went to work and when I got it out and rinsed it almost 12 hours later it was still well seasoned, the next time I used it the griddle worked fine.

Another time when soap can be handy is when you have cooked something that leaves a lot of grease behind such as a pot roast or turkey; leaving grease in a dutch oven for a couple days can turn it rancid especially in hot weather and if it has not been stained and has food particles in it, the dish soap just makes it quicker and easier than using paper towels to wipe it out.

Many times I have been told to not use soap because the pores in the cast iron will soak it up and anything cooked in it will have soap in it.  Well the surface of the cast iron has some microscopic pores in it, true, although the carbonized oils are supposed to fill them, but what is more important is if these pores are not fully filled with the seasoning any soap that goes in them is so minute as to not be noticed, plus it will rinse out just fine, the cast iron is not as porous as many think, if it was the oil and anti-freeze would seep out of any cast iron engine block also.

Another item to use for those really tough to clean messes is washing soda (Sodium carbonate which is not the same as baking soda or Sodium Bicarbonate) available in the same area as laundry detergent in most stores.   This is not soap, but it does soften the water so it cleans better than plain water, also if one has to deal with hard water it will soften it so any soap or detergent will work better.

One item often said to be bad on cast iron is the dish washer, I do not having one of these devices so I can say I have never tried one with cast iron, but rather than the dish washer itself being the problem, my thoughts are it’s the piece sitting wet in that damp environment that causes the problem, wash a cast iron piece with any method using water and let it slowly dry in a damp environment and you will get rusting, not anything you can’t fix, but it will rust.

So we have the piece cleaned, the seasoning is still there, but it needs a wipe with oil to keep it from rusting, what oil/fat to use?

The problem often lies when a piece is used and when dry oil is wiped on it to stop rusting, a drying or semi-drying oil will get gummy in time, the time factor is based on the iodine value.

I have always preferred olive oil for wiping a piece that will be stored over a couple of weeks, just a thin layer put on with a rag works well, for short term I often use lard, this is one pieces that get used often, my most used kitchen pieces and my camp ovens when cleaning up to go home from a trip.  Then for storage I clean them up and use olive oil on them.

We can see that the 3 oils from the palm family (coconut is a palm) have a lower Iodine value, I can’t remember ever seeing palm oil or palm kernel oil other than on ingredients on things like chips, the coconut oil has the lowest value but the cost is very high and the olive oil always comes in under the wire as a non-drying oil.

No matter how the cast iron was cleaned, a thin coating of oil and the oven being heated for a period of time is the way to season it, the times and the temperatures vary with who ever is telling how, I long ago concluded that any where from a ½ hour on up and at 300F to 400F will work fine, I often just grease it up with lard and bake bread in it, it seems to work fine for me and I don’t waste heat on an empty oven.

I see mineral oil recommended at times for both seasoning and preserving cast iron; on the plus side it rates a 0 on the Iodine Value so it has no chance of getting gummy.  But to me the down side is it’s a refined petroleum distillate and although there is a food grade mineral oil, it is intended more as a lubricant for food processing machinery, its use in food products is very restricted by law.   One of the medical uses of mineral oil is a laxative and there are many cautions on its uses in that field, I just prefer to stay away from it although some who use it swear by it.

When it is all said and done, just about any food grade oil will work for preserving our cast iron after cleaning, but we can see the true non-drying oils are more forgiving when you get it on a little thick and animal fats do run a risk of turning rancid, to me it just makes sense to stick with a vegetable oil that always falls under the non-drying oil status.   Of these for me at least the olive oil gets the go, it is easy to find at almost any grocery store, it is something I generally keep in the groceries because it is correct to the 19th Century and has some uses for me in cooking.   For others some of the other non-drying oils may make more sense.

I am often in a hurry when I clean up my cast iron; I often cook for large groups and run 10 or more ovens, if I’m cleaning them myself I am often also getting another meal going and I end up hurrying, if I get too much oil on an oven and that one don’t get used for a couple days the soy bean can already be starting to get sticky in the summer heat.
Also often I have someone who is a camp helper who many not have any real skills with cast iron cooking but may be doing things like dishes and general camp chores, often this involves cleaning dutch ovens and re oiling them, I am sure not going to ride herd on someone, because most times the help is volunteer and I don’t want them to think I’m being picky,   A non-drying oil means if they get a bit too much oil on a cast iron and it doesn’t get used right away, then is not going to get sticky and gummy after a while.

Since most times all I carry in camp is lard, that is what gets used in camp, after the season is over I just use olive oil in a thing layer after cleaning the ovens to store, also I use olive oil at home most of the time, because I keep it stocked in the cupboard.

To vary from this requires I buy another item and in camp it means I have an extra item I have to take to camp, I just prefer to keep things as simple as possible.