Cast Iron Cleaning With Lye

Notice: Lye is a caustic substance. It can cause skin burns, and blindness if it gets in your eyes. Undiluted, or if handled improperly, it can be quite hazardous. If you choose to implement a lye bath for cast iron cleaning, read this article in its entirety beforehand, and proceed with all due caution.

Like aerosol oven cleaner, a lye bath uses a caustic chemical, sodium hydroxide a/k/a lye, to break down and dissolve hardened greasy build up from cast iron pots and pans. Compared to spray oven cleaner, a lye bath can be very cost effective in that it can be re-used over and over, and can also clean multiple pans at once. Another benefit is you can clean pieces according to your own convenience, leaving them in the bath as little or as long as necessary, or even longer.

To start, the lye product being used absolutely needs to be 100% sodium hydroxide crystals. Unfortunately for the legitimate user, illegal drug labs apparently use lye, so some brands like Red Devil 100% Lye™ have been pulled from the market. Crystal Drano™ has lye in it, but it also has other stuff you don't want. Rooto™ Household Drain Opener and Roebic™ Crystal Drain Opener, however, still sold at Ace Hardware and Lowe's, respectively, are 100% lye. Similar products which expressly state a composition of 100% lye (sodium hydroxide) can also be used. Other sources of lye include suppliers of soap making ingredients.

One pound of lye crystals per five gallons of water is the formula. Always add the lye to the water, never the reverse-- it will create a thermal reaction which can cause it to boil up and splash on you. Even when mixing and using lye properly, always use skin and eye protection, and protect clothing or wear clothes that it won't matter if some might drip on them.

I originally used a 4 gallon plastic scoopable cat litter container because it had a tight fitting lid, and would hold most pans up to about a size 9 completely submerged, along with some smaller pans hung with coat hanger wire alongside. I later replaced it with a 20 gallon Brute™ trash can with a locking lid. Any similar, sturdy container capable of holding its volume in water, with a secure cover to keep out inquisitive children or pets will also suffice. Over time, plastic containers not made of UV resistant material, if used outdoors, will become brittle and need to be replaced before they crack and leak.

Depending on how thick the build-up on the piece is, it will take from a few to several days for the lye to soften and dissolve the crud. Be sure to rinse the piece well before proceeding with initial seasoning.

Other things to know about lye:

  • The warmer the lye solution is, the faster it works, so in a sunny spot is best.
  • Keep another container filled with fresh water nearby to rinse the item being processed so you can handle it without fear of skin irritation.
  • Even after rinsing, residual lye solution will make the piece slippery, so handle carefully.
  • You can leave a cast iron pan in the lye bath virtually indefinitely without concern; the high pH of the solution actually works as a rust inhibitor.
  • Even when the solution over time becomes black as coffee from removed crud, it will still be quite effective. I have used the same batch of lye for more than a year to clean dozens of pieces.
  • Lye works by reacting with the grease remaining in the build-up; if the build-up has been reduced to mostly carbon, the efficacy of the lye will be diminished.
  • Since lye will not remove rust, the usual protocol when using both lye and electrolysis is to de-crud with lye first, then finish with electroysis to remove rust and any remaining crud.

A word about the use of lye: I have had at least one person tell me that lye should not be used because it is "toxic" and environmentally irresponsible. I do not believe either to be the case when used and disposed of properly.

Lye is a caustic substance, meaning it has a pH that is extremely alkaline. To be toxic to humans or animals, it would need to be ingested. Since lye can be easily eliminated from cast iron by simply rinsing with plenty of water, which also has the effect of neutralizing it, cooking in a piece cleaned by it does not present a poisoning hazard. Properly diluted for disposal, a lye solution will not even kill lawn grass.

Lye (sodium hydroxide) is a naturally occuring substance leached from wood ashes. It has been used for centuries in the making of soap. It is said without lye, there is no soap.

There is such a thing as food grade lye. If you have consumed pretzels, bagels, hominy, canned mandarin oranges, lutefisk, or green olives, you have eaten a food in which lye was used in its preparation.

This is not to say that lye is not dangerous. It can be, under various circumstances, if mishandled. At the strength used to clear clogged drains, lye is absolutely hazardous to anything organic it contacts. At the concentration recommended for cast iron cleaning, it is still a skin irritant and potentially damaging to the eyes. But, if handled appropriately, carefully, and with due respect, it is a perfectly acceptable means of cleaning cast iron cookware.

Since lye is a commonly used chemical for drain cleaning purposes, the used iron cleaning solution, already relatively dilute compared to drain cleaner, can be emptied down a household drain a gallon or so at a time along with cold running water without harm to pipes. Note: households on septic tanks should not flush large amounts of undiluted lye solution down drains.

Some believe the lye solution should be neutralized with an acid before disposal, recommending the use of household vinegar to counteract the alkali. This is unnecessary, as simple dilution with plenty of tap water will easily drop the pH to non-hazardous levels. Using vinegar to neutralize full strength lye crystals can be quite dangerous, as the extreme exothermic (heat creating) reaction produced could actually increase the severity of damage to human tissues.

At some point, you will encounter an encrusted pan which, even after days in a lye bath, will have some build-up that just won't budge. Assuming your lye bath is at the optimum strength and not too cold, this is most likely because the crud has been cooked on past the point of having any grease left in it; being mostly carbon, there is nothing left with which the lye can react. In such a case, the options are either a lot of elbow grease scrubbing or wire brushing, or electrolysis.

Lye can safely be used to clean nickel or chrome plated pieces. Lye should not be used to clean enameled cast iron pieces; it will dull the finish. Lye should not be used to clean cast aluminum ware as it will dissolve it.