Turning Grease and Trimmings into Lard, Cracklins, and Soap

NOTE: This is a long post and is way too technical at times.  We should have probably broken it up into two posts--how to render lard/tallow and then how to make soap out of it.  But we wanted to keep the whole process in the same place, as a single reference.  Hopefully some of our readers will appreciate the thoroughness.  If you are not one of those readers, apologies in advance.

Last weekend, we wrote about saving our bread crumbs in the freezer to turn into schnitzel.  We do a similar thing with our meat trimmings and leftover frying grease, and bacon drippings.  Except we don't make schnitzel out of them.  We make cracklins and soap.  Very little goes to waste, and if we had dogs, none of it would!  It's a many-step process, so let's get started.

We started collecting meat trimmings and leftover grease in canning jars in the freezer.  When we decided we had enough for a good batch of soap (which was this weekend), we thawed them out.

We sped up the thawing process in the microwave.

After two minutes or so, the trimmings are liquidy enough to scoop out of the jars and into a single bowl.

We added a few cups of water to the mix.  The idea is to get everything liquid, and impurities in the fat will settle down into the water layer.  Another five minutes in the microwave and a lot of the fat is melted, but a good portion of the trimmings are still solid.  That's ok for now, it just means that they had a lot of either very high-melting fats or non-fatty material.

A second five-minute stint melts quite a bit more of the fat, and with that, we'll set it in the fridge and let it cool down.  With the light shining from the top, it's easy to see that most of the impurities have gone into the water layer and the fat left on top is nice and clear.  Yay, we're rendering!

After a few hours the fat is what amateur scientists might call 'recrystallized'.  It's pretty white, but there are still some brown things in the fat. 

So we'll scoop most of the fat into another bowl (left) and discard the water (gasp!).  If we had a dog, we'd give it the water as a treat.

We switched the fat back to the other bowl, added more water to the scooped out fat and microwave it again for 5-10 minutes.

More of it is melting, and some solid specks are visible at the bottom of the bowl.

Then we take it out of the microwave and scoop out any big pieces of solids that haven't melted yet.  These must be things mostly not fat (or really high-melting fat).

Now we've got one bowl of slightly-less-fatty solids and one bowl of clean fat on top of dirty meat-water.  The second bowl goes back into the fridge to solidify the fat again.  After that, we'll get rid of another batch of water.  What a lucky imaginary dog we have!

The first bowl goes into the frying pan to make cracklins!

We let them cook down for a few hours.  Some additional fat will melt, and the rest will fry down into a tasty toasty batch of delicious.  Some folks recommend not making cracklins in the indoor kitchen because the whole house will smell like cracklins and they will splatter oil everywhere.  We're not sure why the first reason is bad, but we went with a low heat and didn't have much splattering or odor.

Here they are cooked down, stewing in a delicious bath of their own making.

We drained off the fat into the other bowl and stirred it up a little bit to make sure any non-fat parts of the cracklin grease get extracted into the water layer.  (If upon solidifying, impurities in the fat layer are still visible, you can do another step of removing the water, adding clean water, melting everything again, and removing the water.  Hopefully your dog has been really good.)  Then we seasoned the cracklins (a few sprinkles each of salt, pepper, garlic powder, cayenne pepper, and Tabasco sauce), then took the spoon and broke up the cracklins into small pieces (after trying a few, of course).  We use the pieces like bacon bits.  We're eating ours on chili this week. They are not healthy, but they are good.   Everything in moderation.  Mmmmm.

We'll need to know the weight of our purified grease, so we're going to start by weighing our now-empty bowl.

...And now with the fat in it.  Some folks use this grease (mostly lard for us) as a foodstuff largely equivalent to modern-day vegetable shortening (after it solidifies).  Lard has gotten a bad rap as being unhealthy, but actually has a healthier lipid profile (less saturated and more unsaturated fat) and lower cholesterol than butter.  (According to Google anyway.  How does Google know this stuff?)  It's certainly not a health food, but to dismiss it as less healthy than shortening or butter isn't fair, either.  (Keep in mind that lard rendered this way is likely better than store-bought lard, which has often been hydrogenated just like shortening.)  Anyway, we've got more of a need for soap than pie crusts for the time being, so we're going to turn our lard into soap.  The following process is what's described as cold-process soap.

At this point it's probably a good idea to review the soap-making process.

<chemistry-dense section>
Lipids such as vegetable oils, beef tallow, and lard, are made up of triglycerides, or TGs.  TGs are made up of a glycerol 'backbone' and three fatty acid tails (the tails are often abbreviated R or R' or R'' by lazy organic chemists).  Saponification breaks the tails off the glycerol backbone using a basic reagent (normally NaOH or KOH), which forms glycerol and a fatty acid sodium (or potassium) salt (i.e., soap).  Each type of lipid (and even the same type of lipid from different sources!) has a different fatty acid profile in its makeup (some of the tails will be longer or shorter, or have different numbers of double bonds (which makes them 'unsaturated').  Because the the oil and base react on a number basis and not on a mass basis, therefore, an ounce of different oils will require different amounts of base to react fully into soap.  This feature is reflected in a characteristic called the saponification number, or SAP number for short, which is formally defined as the mass of potassium hydroxide (KOH) in milligrams (mg) required to fully saponify one gram of a given oil.  These numbers will typically be in the 100-200 range.  Many times, however, SAP numbers are reported as 'grams per gram' or 'ounces per ounce', which are different by a factor of 1000 (they'll be in the 0.100 to 0.200 range).  SAP numbers are tabulated in many places, including online (of course), and many tables give a range, or give values that differ from other tables because of the inherent variability of an oil type's chemistry.
</chemistry-dense section>

An example of how a SAP number is calculated from an oil's composition is given in the spreadsheet linked here.  The spreadsheet also shows how to use the SAP number to make a soap recipe for a given fat composition.

Anyway, we estimated that our fat was about 70% lard, 15% beef/venison tallow, and 15% olive oil, and we had 21 oz. total.  That means we had 14.7 oz. lard and 3.15 oz. each of tallow and olive oil.  The SAP values for those are 0.138, 0.140, and 0.134 for NaOH, respectively (it would be different for KOH), which works out to 2.89 oz. of lye to fully saponify the fats (multiply the amount of fat by the corresponding SAP value and add them together).  Normally, a 'lye discount' is used to leave a little bit of the fat intact.  That makes the soap less harsh.  We took a lye discount of 9.5% (requiring 2.62 oz. lye), which is pretty high.  But we know that the cooking process itself will start to break up the triglycerides, and used cooking oil will often contain ~5% free fatty acids (i.e. material that doesn't need lye to become soap).  So we eased off on the lye to account for those as well.

Where do we get our lye from?  We found what we were looking for in a certain type of drain cleaner, but we had to be careful that it says 100% lye or 100% sodium hydroxide on it and is white in color.  Other ingredients might interfere with the saponification, and might be dangerous to clean yourself with.  (Unless you're a drain pipe.  If you can read this, you're not a drain pipe.)  Soapmaking and biodiesel sites can also be good resources for where to find good-purity lye (or make your own!).  It's important to have a good soap recipe.  There are plenty of good links on the internets, but we like a ratio of about 6 oz. water per 16 oz. fat, and lye according to the saponification (SAP) number, minus the lye discount.  Also, for our lye, which is in granulated form, we found that one ounce of the granules equals 1.814 tablespoons (by weighing a half cup and dividing by eight).  The small amounts are easier to measure by volume in a tablespoon than by weight on our mechanical kitchen scale.  The density used to be less than that--this lye is a couple years old and lye in general is hygroscopic, which means it will take on water from the atmosphere.  That can affect your measurements, so make sure to keep your lye tightly sealed.  In effect, we're actually taking a larger lye discount than we calculated above because some of the 'lye' we're weighing out is really water.  But in our case the water content hasn't changed too much, so our calculation will still work.  So our final recipe is 21 oz. rendered fat, ~1 cup water, and 2.62 oz lye.  SAFETY NOTE: All steps with lye should be done wearing rubber gloves and goggles!  If any lye or lye solution gets on your skin, rinse it off right away with lots of water.  Don't let any get in your eyes.  That would be very bad.  If it does, flush with lots and lots of water and get to a doctor.

We mixed the lye and water.  Add lye to water, not the other way around, or the first water you add could get superheated and pop, sending caustic ooze flying around the kitchen.  Caustic ooze makes Katie unhappy, especially in the kitchen.

It will get hot.  Normally hotter than this.

When it cools down a little (to ~110 °F or so), we added the lye solution to the fats and stir.

We keep stirring until the soap 'traces.'  That means the spoon stirring through the liquid will leave a visible trace (or something like that).  Anyway, when it's the consistency of warm molasses, it's traced.  In chemistry terms, that means the saponification reaction has gone far enough that the fat and the water we mixed together won't phase-separate anymore, and we can pour it into our soap mold. (Oh yah...we need to build one of those...)  Before we do that, though, we add any other ingredients we might be thinking about--little pumice scrubber things, girly herbal things, or something to make the soap lather better, because standard soap molecules by themselves don't make much for bubbles.  Castor oil is commonly added to increase lather, but we didn't have any on hand.  Why does castor oil work well?  Because the fatty acid chains have hydroxyl groups on them, which interfere with water's surface tension.  (A bubble's film needs an optimal viscosity-to-surface tension ratio and a slow water evaporation rate to be stable, and the hydroxyl groups in castor oil move the soapy water's properties closer to that optimum, mainly by reducing water's surface tension via disruption of it's hydrogen bonding network.)  So, what if we added something else with hydroxyl groups?  Like sugar or honey--it will work!  We added about 1.5 tablespoons of honey at trace.  Katie likes bubbles.

A glass dish like this functions ok as a makeshift soap mold.  This will be the final shape from which we cut our soap bars, so we have to make sure it's nice and smooth.

That's better.

After sitting for a few days, and it will become nice and solid.  After a week or so, we'll take it out of the pan (hopefully in one piece), and cut it into bars.  It will need to cure for another month or two before it will make good soap.

UPDATE 10/4/2013: We cut it into bars and it's now curing.  Here's some pictures:

After a few days, the soap should be solid enough to take out of the mold and cut into bars.  We used a flipper/spatula thing (the device used for flipping hamburgers or removing cookies from a cookie sheet post-bake).  We got lucky this time and the soap all came out in one big, chic-looking piece.

Then we cut it into bars and spread it out on a plate so it will cure faster.  Also, to teach a lesson to any hungry burglars thinking we have a plate of cheesecake bars or something on top of the fridge.  Don't forget to brand the bars, if you're into that kind of thing.  We'll leave it like this for 6+ weeks, though others say it would be fine to use sooner.

Then we washed the soap mold.  Guess what!  We didn't even need to add soap!  That must be the cleanest dish ever.

Do you have other soap-making tricks?  Have you ever done it with wood ashes as your lye source?  What else do you do with scraps from your meat-trimming operations?  Let us know in the comments section below!