Dealing with spent cooking fats

I was just hand washing a mountain of dishes and got to thinking of something I've wondered about often: what's the best way to deal with spent cooking fats?  I did several searches here on Permies to see if I could find an existing thread, and nothing came up.

Once in the past I took a pot of spent frying oil (peanut, probably) out into the yard and dumped it onto a small patch of out of the way lawn.  This idea came from a cooking show I had seen about deep-frying a turkey.  This resulted in a dead patch of lawn for several years.

In my household, we'll have a deep-fry dutch oven going maybe 2 or 3 times per year.  Once I deem it spent (as in, the fat has broken down too much after multiple heatings, and is no longer safe to use, no longer smells ok, and the fried food doesn't taste as good, or get as crisp), what's the best way to deal with it?  I currently live in a place where used cooking oil drop off points are widespread, and so I've been doing that with store-bought oils.  But, about every third time I start a deep fry pot, it's home-rendered animal fat.  I assume this would not be accepted at the recycling points.  So, I've frozen it, and discard the solid block.

I'm wondering what would/should be done with either of these fats on the homestead?  Can you compost it?

I'm not on a homestead, but I do end up with cooking fats that I certainly don't want to go down the drain. I have a few strategies.

I may find a place away from foot traffic in a corner of a garden, and pour the grease there on the ground. The local bacteria will eventually take care of it.

Another option is to collect and freeze it. During the winter, I may plop a glop of the fat in an area where the birds frequent, and they will nibble it down over the course of a few days. Some people tuck the fat into a pine cone and hang it up in a tree. Fat is hard to get in the winter, and they'll be happy to get it. The cold keeps it solid, or nearly so, and noticeable to the birds.

My other strategy is to either pour or glop a chunk of the fat in a corner of my worm bin, buried a few inches down to discourage smells. Yes, worms will eat the fat. Worms will eat nearly anything biodegradable. I put it in a corner so that they can go get it if they want, and stay away if they don't. Also, being limited to a corner, they can lead in mouth first and back away if they want to keep the fat off of their bodies.

This is almost the question I am looking for an answer to I need to get rid of liquid oils, (no collection points here)  I've seen suggestions about giving it to chickens mixed with their grain, but the body condition of my chickens is fine so they do not need the extra fat, I cannot consider dumping it somewhere on the ground because I have two dogs, they would soon be eating every little bit of soil that had any on it. I wondered about burying it.

Now I also have 5 gallons of palm oil (solid!) I was gifted for soap making, not even made a dent on that and won't before it goes off, so another thing to figure out.

Would there be some way to turn it into firestarting? hmm maybe I could use the liquid stuff to start this winters bonfires.

Fire and chickens. Soak the chickens feed,soak the fuel.

I second feeding it to the chickens.  I often give my used cooking oil and accumulated grease/fat to the chickens.  Usually mix it in with some grains, old bread, or whatever other scraps I might have around to soak up the oil.  The birds love it.  l sometimes mix a batch of grease with grains to make suet cakes.  You can throw them in the freezer and then feed out as treats though out the winter.  

If the oil is really old or gone rancid then I'm not sure if it would be ok for chickens or birds.  In that case I like the idea of soaking wood or cardboard in it to make fire starters.  

I had the same experience with a dog. They will not leave that spot alone. I have some serious rock piles that could have fat dumped into them. Rocks are too heavy for dogs to rip apart. I suppose it's possible that a bear could rip the pile apart. The only issue then, would be that vermin might live on the fat.

During the heating season it's quite simple. Put it in a big roasting pan or something and soak the kindling. Before burning it, I would first offer it to chickens, pigs and wild birds. In winter, wild birds really want to eat fat.

When I lived in the northeast, to offset the cost of natural gas I built a veggie-oil burner and heated my house for several years that way.  I bought used vegetable oil from a gentleman who  converted his Mercedes diesel to run on vegetable oil.  So having hundreds of gallons of used oil on hand I experimented and made soap.  Wonderful unscented soap.  It doesn't matter if the oil smells like fish and onions.  It won't after being converted to soap.  You could also use your oil in a home made oil lamp such as these:
https://modernsurvivalblog.com/alternative-energy/do-it-yourself-olive-oil-lamp/

One permie solution is to give away or share your excess. Around my area there are public bulletin boards (at food stores) where I can post a note about free stuff I want to give away. I can safely meet a person at the store to exchange items. Another location I use to make exchanges is our local farmers market. There are lots of people there so it is a safe spot.

When it comes to used cooking oil, I'm the recipient of the exchange. I use the oil/grease for my chickens and pigs. And soaking a rag in grease makes a nifty fire starter.

When we use our deep fat fryer we pour the oil back into the container and put it in the freezer to re use it next time.

When my frying pan get to much oil in it, I make chicken fried steak and gravy.

Another method is to use the oil for baking.  Use it in pie crust and other recipes calling for oil.

Growing up I was taught that frying potatoes purifies the oil so it does not need to be thrown out.

If you must throw it out then freeze it in a container then on trash day make sure the container is well sealed and put the frozen container into your trash.

Here is a great article on what to do with old cooking oil:

http://www.seriouseats.com/2013/09/ask-the-food-lab-how-many-times-can-i-reuse-fry-oil.html

"Good News A: You don't have to throw out used oil. Often you can reuse it many, many times!

Bad News: There's no hard and fast rule for how many time you can reuse that oil. Distrust any source that gives a firm answer on the number times you can reuse oil, including this site.

Good News B: It's easy to tell when you'll need to replace your oil, and more importantly, there are some great steps you can take to increase the useful lifespan of your oil!"

There is also a section on "How to Clean Oil"  and a test:

" If you have some gelatin on hand, you can also give this gelatin-clarification technique a shot. It works like a charm and gives you crystal clear oil overnight."

I have heard of several restaurants that are well know for their 100 year old deep fat fryers or other cooking methods, they never change their oil.

This is the only one that a quick search found.

http://www.dyersonbeale.com/

" Over the years, this famous cooking grease has been transported to our various Memphis locations under the watchful protection of armed police escorts"

This thread makes bizarre reading for me because I go through maybe a tablespoon of olive oil a week. There’s not a lot of spent fats to dispose of on that grease budget! Just another reminder of how differently we all do things.

But if I had them, I’d mix them in rolled oats and feed them to the birds. I don’t keep a bird feeder because of the expense, but wild birds do come in to the outside dogfood dishes, and I don’t begrudge them the calories.

I would add it to our compost heap with plenty of extra woodchips mixed.

Dan, I'm with you. I never deep fry food, nor do I use hardly any oil for pan frying. But if I did, I'd most likely save the oil to feed the birds during the winter....if I lived in a cold climate, that is. But where I am, it's too warm to give it to the wild birds.

Permies are the BEST!  Thank you, all, for so many wonderful responses!

I was going to link the very same article, Anne!  I love that site, and that author in particular.  He mentions Japanese tempura restaurants that say they put a portion of old fry oil into a new batch (the article explains the benefit of this).  I think this must be what Dyer's restaurant is be referring to.  Kinda like an old sourdough starter.  I don't think it's possible to actually use the same oil for 100 years because of the fact that it becomes unstable after multiple heatings.  Unstable means many things, but most importantly for continuing to cook with it, it means that it becomes far more flammable.

One thing the article doesn't mention is that once spent/unstable/oxidized, the fat is very unhealthy to consume, and so, like you, Chris, I would NOT want to feed it to animals whose products (chickens' eggs), or flesh (chickens and pigs) I will eventually consume.  The unhealthy diet of the animals is one of the big reasons I'm not keen on grocery store meat.  If I were on a homestead, I'd pride myself on raising healthy, happy animals.  And, because I know it's unhealthy, I would not want to feed it to wild birds, either (I have made them seed blocks with fresh suet, though.  They love it!  And watching the birds out the window is such a pleasant winter activity).

I'm almost looking at it like a toxic substance that needs to be scrubbed clean by Mother Nature.  So, I'm thinking further down the chain.  Worms!  Good to know, thank you, Ronnie! ...bacteria...?  But, as I said, when I dumped it on the lawn, it visibly killed the grass, and prevented it from growing for a few years.  I assume it killed anything alive in the soil below it, too.  And, so I would also assume that a Dutch oven-worth would create a big "dead zone" in a compost pile, and that wouldn't be good.  So, maybe freezing it into small lumps and scattering it through the compost pile?  I remember reading that Joel Salatin composts all the leftover bits from processing chickens on his farm (must be some fats in there), and I know that composting flesh and fats is smelly..."Extra wood chips," Micheal?  How do the wood chips help?

Soaking fire starters sounds like a good use, too.  I could see my future homesteading self possibly going through those 2-3 Dutch ovens worth of spent fats on that, OUTSIDE, as I wouldn't necessarily want the smelly fat burned in the house.  Again, the broken down oil is more flammable, so this makes sense.  Also makes sense to use it for light, although I would definitely want to know more about that before attempting.  Wouldn't want the lamp to explode.  I was watching an episode of Tudor Monastery Farm on YouTube the other day, and the female host made fat soaked rushes (the water plant) to use as light.  The end result was like holding a stiff candle wick with a flame at the end...a candle without the wax.  Plus smelly smoke.  

I just went back to re-watch that moment, and she describes animal fats as being used as axle grease.  How about this idea?  Anyone have experience with well "used" fat as axle grease?

Back to the fire starter idea.  Maybe a fat-soaked rag or two in a small jar would be a good addition to an emergency kit.

Also great to know that spent oil is fine for making soap!  Thanks, Chris!  That's another thing I can see my future homesteading self doing.

We are very fortunate to be able to afford to almost exclusively eat pastured meats.  I consider the fat from these animals as valuable nutrition, and so we typically consume the fat.  But, as a treat now and then we'll deep fry.  French fries top our list, and next would be homemade tortilla chips.  Anyone ever tried tortilla chips fried in duck fat?!  Oh, BABY!

Again, thanks for the input, everyone!

I'm continuing to think about this...

I guess what I'm wanting to know is, is there a place to use it or put it on the homestead that helps/improves that place?  After the fat has functioned as a cooking medium for me, what is its best next function(s) on the Permaculture homestead?

It killed the patch of grass...could it be used to kill plants that are not desired in a certain area?  Again, though, does it kill the life in the soil, too?

We raise chickens, ducks and geese for food, so I regularly have to deal with the drippings, and my goal is to keep them as useful as possible. The pan drippings go into a glass jar which is cooled so the fat can be removed from the top. I will use it for baking or pastry. Any leftover parts of the bird - bones, sinew, skin - go into a basket in the pressure cooker for 20-25 minutes with water in the bottom, then a glass jar for cooling. The juice makes soup and the fat, again goes for baking. I don't worry about fancy "rendering" and no-one's complained! The remains in the basket go into our woodstove for burning- it's sealed so there's no smell in the house. I'm not sure if you could wrap them in a tube of newspaper to use to feed an already lit RMH - any thoughts anyone? Since the ashes end up on the land, the potassium and phosphorous in the bones will also make it to the land. I have read that the Terra Preta contained bone remnants, so I'm hoping this will have the same effect even if it takes decades or longer. I have also buried bones and fat, but it does attract unwanted visitors, so when possible, I freeze it until we need another fire, or start a fire just for the purpose if necessary even though that seems a waste.

I don't see any reason not to add "home grown/home harvested" fat to an existing fat collection program. Yes, there are differences in different fats from the chemical standpoint (and especially from the health standpoint), but once they've been thoroughly cooked I see no moral reason not to treat them the same as bacon fat. Do you have any idea how your region deals with the collected fat? Is it being burned, turned into bio-diesel, or just land-filled? I admit we do everything we can to keep "useful" or biodegradable things out of the landfill. I agree with the idea of breaking up the fat into smaller bits if composting it. In the past, I've had concentrated fat (from a buried animal) saponify in our wet environment. I've also read that mushrooms (Oyster for one) can deal with oils, so that might also be an option. A permie recently posted pictures of mushrooms raised on coffee grounds. Does anyone know if mixing fat/oil in with their mushroom substrate would work?

From what I understand, fungal processes tend toward the cooler bottom of a compost pile and eat mostly carbon... while bacterial processes favor the thermophilic zone (near the top)  to do they business; Which seems to include eating oils.

After slaughtering a pig, Im in the same boat. Her butchery yielded plenty of fat, which we rendered and are now playing with soaps and lotions and... other ways to smell like biscuits.
However, given that I was a vegetarian until killing this pig; Im not terribly appetized by all the fats and lumps and goops Ive rendered.... and obviously it cant be allowed to waste. Rendering ghee has also yielded a few jars of..... concentrated salt and milkfat. Gross.

The rendered fats are baking bound, and the odd trickles and remnants are chicken bound..... But what can I do with extremely salty milkfat? Feels like giving it to anyone would be sortof toxic, and with so much salt, even my compost pile seems like a potential victim.

Good question

If Belgium has a national fast food it's french fries.

First, slightly of topic but i have to ask. The explanation i heared for the 'french' in french fries is that US soldiers during WWI got to know this food in the French speaking parts of Europe hence french fries. Does anybody know if that's correct ? I've been curious about that since the whole 'freedom' fries thing.


So we produce a lot of used cooking and frying fat. Most of that is recuperated to process it into biodiesel, oleochemicals (soap, paint, cosmetics, ....) and for energy production.
Many major shops have a collection point, every local authority has a least one public collection point. Firms specialising in it haul it away. I put in a link (in dutch) for a firm which does that - no chance that they get to the US but you get the idea.
Besides they support my favorite green charity They have no english website but you can get the drift of their business model with google translate.


The energy production is either by biodigesting (into methane) or direct burning. The residu of the methane production is composted.


Feeding it to poultry, pigs or cattle is mostly no longer allowed after a big food scandal in 1999 brought down our federal government in Belgium. We have much stricter food inspection since - which is not a bad thing - China lacks such regulation and chinese love to import our food. Also people are much more aware about food - permiesculture got a big boost from it.

There are very strict rules here about regularly renewing the oil or fat being used. Partly because of the acrylamide risk. So i'm kind of surprised that one would want to use oil for a long time.

Most of these grenish solutions are not easily applicable for solitary househoulds. Making bio diesel and methane is just about possible on a small scale but it requires chemical and or biochemical expertise that makes it problematic and unsafe.
A locally centralised biodiesel setup could make sense for a farmers coop providing farm vehicles with biodiesel fuel.


https://en.wikipedia.org/wiki/Dioxin_affair
https://en.wikipedia.org/wiki/Dioxins_and_dioxin-like_compounds#Controversy
https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/acrylamide-fact-sheet
https://www.quatra.com/nl


Biological fats and oils break down in soil BUT it takes water, oxygen and 'minerals'.

I once had to investigate a leaking soye oil setup from which several thousand littres seeped into the sandy soil. I could hardly find any residu. Of course the outside conditions where nearly ideal. Medium (grainsize) sand with a forest (mostly coarse pine) litter soil on top - groundwater ~ 1,5m depth, relatively hot summer. For what it's worth. That soil looked positively vibrantly healthy but for a faint rancid mayonaise smell and a fatty feel.

Fat solidifies in the soil and locks out most air and water - so biological breakdown of the fat is limited to the outside surface of the fat. So Corrie that is probably the reason why the grass died of for a couple of years. It effectively blocks out the soil life.

Used oil can contain potentially dangerous chemicals so there is no 100% guaranteed environmentaly safe way to apply used oil/fat in a permies setup. If low in salt (chlorine) burning it at a really high Temperature should produce no to much dioxine.



The situation, i had to investigate was utterly ridiculous as emulsified soy oil is used to stimulate biological break down of chlorinated solvents in soil and groundwater. Unusual situation not covered under standard practice at the time.

The 'minerals' are needed by the bacteria (and fungi?) to help metabolise grease and oil. That is supposedly the reason why oilspills near (horse?) manure piles break down faster. I cannot vouch for that last anecdote. I never found a scientific paper on the subject

Corrie Snell - since you are currently in SF, you could pop over to the Bio-Fuel Oasis in Berkeley and donate it. Other than that you have received lots of good ideas - I will likely in the future use it in fire starting, soap making and oil lamps.

Ian Rule wrote:From what I understand, fungal processes tend toward the cooler bottom of a compost pile and eat mostly carbon... while bacterial processes favor the thermophilic zone (near the top)  to do they business; Which seems to include eating oils.

Rendering ghee has also yielded a few jars of..... concentrated salt and milkfat. Gross.

The rendered fats are baking bound, and the odd trickles and remnants are chicken bound..... But what can I do with extremely salty milkfat? Feels like giving it to anyone would be sortof toxic, and with so much salt, even my compost pile seems like a potential victim.

Unless I am misunderstanding the process, ghee making usually leaves behind milk solids. Traditionally they are used in a dessert dish.
The saltyness of your leftovers suggest you started with salted butter.
 I would bake with this. Cornbread in particular, but any bread that  contains salt might be improved by these solids.

My ellipses betrayed my true confidence in what I was saying

Wound up making a mountain of (yes, salted) ghee to preserve some old garlic-stinky butter for a neighbor, so your suggestion sounds particularly wise.

What is this dessert? Promise I wont use stinky, salty old ghee for it!

I save our cooking grease to make soap. I "filter" out the crispies with paper towel. Then use it to make my soap. I do this before it goes rancid, of course.

Two things you could do with used fat on a homestead that haven't been mentioned; First, pour it into an old stump that you want removed (far from the house) and let a local bear tear out the stump for you while it hunts down the fat. Maybe you are ethically opposed to passing off your rancid fats on a bear but it's an option that I have personally witnessed have fairly spectacular results. The other option I have only heard about and don't fully understand but supposedly you can use fat rubbed all over a fresh cut log to cure it for lumber. I guess it slows the drying process which would avoid any cracking and perhaps help to preserve the wood better. Not sure on that one but I think I read it in Sepp Holzer's permaculture book, so you know it's authentic old timey looniness :). Even for a small homestead though this could be a good use of excess fat and could allow you to insist you're going to get into homestead furniture making once your fat covered logs are finally cured.

Could a drip feed oil system be integrated into a rocket mass heater design to supplement the wood burning? or even design a dual-fuel rmh? The wood-and-or-oil model.

Hate to sideline things but this thread is giving me mighty ruminations - how much is too much salt for chickens and pigs?

The pigs get restaurant slop a'plenty, chickens get their share of scraps, but when I have a mason jar filled with milk solids and salt, or a (used, salted) wad of fat to recycle, is that OK to pour onto the food?

I figure the pigs wouldnt notice given their BMI and current gravy intake, but the chickens strikes me as less able to withstand a mainline of salt.

I pour it on the compost pile.  Done.  The bacteria will make quick work of it.

If you have old stumps that you want to burn, you can drill a couple of holes down into the stump and pour the oil into the holes, or pour the oil into a can with a couple of holes in the bottom and let it slowly leak out onto the stump.  You can drill a deep hole into a stump, fill it with oil, feed a cotton or hemp rope down into the hole as a wick, and light it on fire.  It'll burn for a long time and eventually burn a hole down into the stump.

You could pour the oils on a giant pile of newly anerobic wood chips and cardboard (soaked 2-3 weeks in an IBC tote full of water, maybe don't soak the cardboard though).  Then (now that it's "sterile") colonize it with oyster mushroom mycelium or turkey tail, or whatever.  You should get a helluva crop!  They do this for bioremediation of soil, but in this case, it's non-toxic so you could eat them.  Mushrooms will eat pretty much anything including rocks!  

May be worth mentioning in the vein of burning out old stumps with oil and fire - underground fires arent unheard of around here, and they tend to start either underground or from campers doing Dakota fires or trench burns near roots.

Somebody above already reported positive experiences disposing of fats in a worm composter.  Same-same, I would dispose of any such excess fats, if I ever had any, in my black soldier fly digester.

You're in San Francisco? Surely someone near you is refining biodiesel. I have a neighbor who does that, and that's what my truck runs on. If I have grease he can use, he turns it into motor fuel for me

If you are talking about rancid but otherwise clean oil, use it to lubricate things.  It is my preferred oil in my shop.  Oil your hinges, any little machines you have around, the bottom of planes, guns, prevent rust on tools, or anything else that needs some oil.  I also use it on my oil stones for sharpening.  If it is a polyunsaturated fat that does not harden in cold weather and really clean, then you could also use it as bar oil on a chain saw.

Dirty cooking oil from frying is probably better to feed to animals as other people mentioned.  You could also use it to make or feed an oil lamp though it will smell like cooking oil.  Soldier flies would certainly get rid of it quickly in warm weather.

But what can I do with extremely salty milk fat? Feels like giving it to anyone would be sort of toxic, and with so much salt, even my compost pile seems like a potential victim.

With the intention of making gjetost I would simmer down the whey from my cheese making but discovered it was too salty but the cheese was to bland lacking salt so I mixed the still hot reduction back into the cottage cheese and the results was perfect balance of salt and caramelized flavor.
Inedible oil would be the ideal fuel to get a RMH up to temperature because it makes a relatively clean creosote free flame. I personally start my fires with the paraffin soaked boxes from the produce department at the big box store. They are happy to give it to you because it can't be recycled.

I have a gazillion pine cones from several happy donor trees. I use the best for crafts and the less than perfects get soaked in the fat... let to sit and drip onto old paper or cardboard, and used as firestarters. Both the cones and the soaked cardboard.

I think the one of the main reason why oil kills grass/weeds is because it causes an explosion of fungal life and they out compete the roots of plants when they dont have to depend on the plants for a slow and steady supply of carbon.  https://phys.org/news/2014-05-fungi-oil-polluted-soil.html

Hans Quistorff wrote:[I personally start my fires with the paraffin soaked boxes from the produce department at the big box store. They are happy to give it to you because it can't be recycled.

That's exactly what I do. I never again have to bother with kindling.

The paraffin boxes are how we started fires in the wood burning pizza oven. We would fill the box with wood, lite it on fire and then push it to the back before the box burned completely. Some restaurants would dump sterno fuel on the wood, but that seems so wasteful. I don't think it ever occurred to restaurants to get kindling.

Stacy Witscher wrote:Corrie Snell - since you are currently in SF, you could pop over to the Bio-Fuel Oasis in Berkeley and donate it. Other than that you have received lots of good ideas - I will likely in the future use it in fire starting, soap making and oil lamps.

It's not even necessary to cross the bridge!  There are oil drop-off points at my neighborhood Whole Foods and Rainbow Grocery, and I've used those for the vegetable oils.  I did go to Bio-Fuel Oasis's website, and it says that their fuel is made from "recycled vegetable oil," so I imagine they'd reject spent animal fats.

Thank you!

Thinking of this as an upcycling/downcycling issue... and trying to get the best value, maybe even get something better in return (like human food).

After a human use, it becomes a food by-product and if it hasn't spoiled or degraded, it could be used as animal food (wild or domestic).
Next, the oil/fat is a fuel source, first as an engine fuel (WVO, biodiesel) then as a heating/lighting? fuel (oil furnace, fire starters, other pyromaniacal ends) or lubrication.
Then, insect food (BSF) to convert to animal feed.
Followed by, composting.
Last resort, garbage.

So, would one discontinue cooking with an oil sooner to maintain it's food value for animals? Maybe, if you don't have a need for a fuel...
Or maybe you use it longer, with the knowledge that you're going to make it into fuel, since you don't feed any animals anyway...
Or maybe you share with someone who CAN use it for something higher on the list than you would have used it for, maybe you trade it for a pie!

I'm overwhelmed with great information.  Thank you, Permies!

As I'd said, I'm looking for best next function for the fat in a Permaculture setting.

Feeding it to the bacteria and fungi in the compost pile, or to worms or soldier flies seems simple and perfect.  Feeding it to fungi that will eventually grace my table sounds delicious.  Greasing tools is another good one (thinking of Laura Ingalls Wilder's Pa and his bear grease!).  Soap-making, awesome.  All ways to keep the fat on the land.

On the wood preserving idea (from Sepp, via Stephen Lowe!), that brought to mind a thing I'd just learned about from another daily-dish, the Japanese method called "shou sugi ban," as featured in this video.  I wonder about using, again, "spent" fat, and, again, animal fat in this application.

Wow, Erwin Decoene!  Incredibly interesting information from Belgium!  To answer your question, yes, I've heard the same thing about "French Fries."  And, from your post, the idea of feeding the oil to a methane digester is quite intriguing.  I've been fascinated by that process, and it's possible use on my future homestead for years.  It seems that there are several options out there now for individuals interested in trying this out, but who aren't interested in building their own system.  For example, the product mentioned in this thread.  On their website, they say one can add fats and oils to the unit.

I'm no longer seeing a problem...only the solutions!

I use it to paint fence posts (especially the tops) and boards. And paint the boards of the utility trailer a couple times a year. If I had enough, I'd paint it on the t1-11 siding across the back of my shop...