Eggshell (Calcium Carbonate) Leavening, Part 2

If you've been following this blog lately, you know that we're engaged in a multi-week battle of wits with a pile of eggshells.  Specifically, we're trying to figure out a way to isolate calcium carbonate from eggshells to use as a leavening agent.  The calcium carbonate is bound up in a matrix of protein that makes it less accessible for leavening action, so for maximum leavening effect, we have to either dissolve away the protein or dissolve away the calcium carbonate and then regenerate it.  Last week, we tried boiling ground-up eggshells in lye to dissolve away the protein.  (It didn't work very well, but at least the biscuits were tasty.) Today, we take a look at the other option--dissolving the calcium carbonate and regenerating it.

The first thought we had was that the CaCO₃ in the eggshells can be dissolved by the acetic acid in vinegar to make calcium acetate (Ca(Ac)₂), which can be decomposed to CaCO₃ around 400 °C.

Unfortunately, some of the eggshell proteins are also apparently soluble in vinegar, and when we made calcium acetate by dissolving eggshells in vinegar and evaporating all the liquid, we ended up with a light-brown colored solid, which yielded a gray powder after a clean cycle in the oven (which gets close to 500 °C).  We got a similar looking powder when we put ground whole eggshells through the oven clean cycle.

The product from calcining eggshells in the rocket silo was actually a little darker colored.  As a point of reference, we're looking for CaCO₃ as a fine, white powder.

This is actually a problem that's bothered us since we wrote about grinding up eggshells way back when this blog was just an infant.  While it's usually possible to burn organic matter (e.g., proteins) off of inorganic residue (e.g., wood ash, glass, stainless steel) at 400-500 °C (750-930 °F), eggshells hold on to the organic matter from their protein until 900 °C (1650 °F).  Unfortunately, at that temperature, our desired CaCO₃ has transformed into lime (calcium oxide, CaO).  Thus, it's no surprise that when we put a pile of eggshells in our oven and set it to the clean cycle, our pile came back grayish-colored instead of the white color of pure CaCO₃. (Although, we were surprised at the time since we hadn't done much reading on the topic!)

So, we're 0-for-2 on getting our pure CaCO₃ out of the eggshells at this point, but it's worth noting two things.  First, while we haven't been able to get pure CaCO₃ from eggshells, the gray powders from either the decomposed eggshells or the decomposed calcium acetate react much more vigorously with vinegar than the raw eggshells.  Still not as vigorously as baking soda as the video below shows, but bubbles abound nonetheless.  So, maybe the gray powders are worth trying as leavening.

Second, can we approximate a best-case scenario for obtaining pure CaCO₃ from eggshells?  Yes! We can get a bag of pure CaCO₃ for a couple bucks at the local homebrew store.  So while our blog post declaring victory on purifying CaCO₃ from eggshells will have to wait until another day, we can still see what a best-case scenario for eggshell-based leavening would look like. Biscuit baking time!

Same recipe as last time, but only four sets this time: no leavening, gray CaCO₃ from eggshells, white CaCO₃ from the homebrew store, and NaHCO₃ (baking soda).  Very similar results as last time, too.  The gray CaCO₃ biscuits are definitely more risen than the no leavening control, and similar to the biscuits we baked last week from raw and lye-boiled eggshells.  The white CaCO₃ biscuits were noticeably more risen than the gray CaCO₃ biscuits, but still couldn't hold a candle to the baking soda biscuits.

The textures of both sets of CaCO₃ biscuits were similar to last week's results, too. Not completely cooked through at the 20 min mark, while the baking soda biscuits were definitely done. 

The effect is more pronounced for banana bread.  Can you guess which loaf used gray CaCO₃ from eggshells as leavening? (Hint: it's not the one on the right--that one had baking soda.) The grand conclusion from all these experiments?  Even though the CaCO₃ releases carbon dioxide gas when mixed with an acid (same action as baking soda), the slower reaction kinetics mean that eggshell-based leavening can't get the job done.

Have you ever baked with eggshells or tried to isolate CaCO₃ from them?  How did it turn out?

EDIT: After going through our wood ash leavening experiments and realizing that we could get good leavening effect by incorporating more of the leavening agent, we came back and baked another set of biscuits with 1 tsp of the finely-ground eggshells (i.e., with quadruple the amount of eggshells of our recipe).  The biscuits were definitely still not as light and fluffy as the baking soda-leavened biscuits, but were better than anything we had achieved so far, and actually, not too bad on texture.  So, if you do any experimenting on your own, start with at least four times the volume of ground eggshells as the recipe calls for in baking soda (e.g., if the recipe calls for 1 tsp baking soda, use at least 4 tsp ground eggshells).

Homestead Happiness, February Week 3

We're still fine-tuning some of the experimental details on our eggshell leavening, but it was otherwise a productive week around the homestead (thanks to some unseasonably warm weather!).  Here's what made us happy this week.

We got another batch of wine started, this one from frozen black raspberries.  They had been in the freezer since July of 2004!  They say a fine wine improves with age, guess we'll find out if that applies to aging before fermentation, too.  At least, the berries still tasted good!  Also, starting the wine meant Jake could clean up the mess that the berries made in the fridge while they were thawing.  That made Katie extra happy.

Outside, highs in the 50s and 60s (°F) made for happy playing in the dirt, including playing musical berries.  We transplanted dormant strawberries out to the garden where we can protect them with the motion detector sprinklers, and dormant raspberries to the place vacated by the strawberries since they weren't thriving in their original location.  Also, 'Musical Berries' is going to be the name of our new family band.

Also on the yard work list was chopping out the remaining stump from the tree of heaven, filling the hole with dirt, and planting another tree in it's place.  Some of the old stump pieces had termites, which the chickens liked a lot.  In fact, they were willing to brave a battlefield of flying wood chips to get to them, and with 100% survival rate.  We've got ninja chickens! (Never mind, we're going to call our band 'Ninja Chickens.')

In the process of our eggshell leavening experiments, we also made a big pile of wood ashes, which we'll use in a future set of leavening experiments.  The connection between these two will become apparent in the near future.

The rhubarb is alive!

The chives are also alive!  It's always nice to know the plants are starting to think springly thoughts, too.  The weather, on the other hand, is very ambivalent--after highs in the 60s on Saturday, we got a nice blanket of snow last night!

The chickens are also revving up their egg production--four eggs in four of the last five days.  Keep up the good work, ladies!

What made your homestead happy this week?

Eggshell (Calcium Carbonate) Leavening, Part 1

A few weeks ago, we were reading a 5 Acres and a Dream blog post about making homemade leavening from wood ashes (i.e., from potassium carbonate, K₂CO₃), and a reader in the comments section asked if calcium carbonate (CaCO₃) from eggshells, which also reacts with acid to release CO₂ gas (reaction below), could be used as a leavening agent.  We had been wondering the same thing for quite a while, and the realization that other folks were wondering the same thing provided the motivation we needed to finally get up and do some experiments.

Calcium carbonate (CaCO₃) reacts with acetic acid in vinegar to make calcium acetate, carbon dioxide gas (CO₂), and water (H₂O).

First, some eggshell chemistry.  Eggshells are about 95% CaCO₃, but the CaCO₃ is bound in a matrix of protein, with a proteinaceous membrane also attached. Thus, one might expect that eggshells would make a better leavening agent if the CaCO₃ could be isolated from the protein (and/or ground very finely) so that it would be more accessible to the acid during baking.  The question is, how to get rid of the protein?  We'll have to either dissolve the protein away from the CaCO₃ or dissolve the CaCO₃ away from the protein and then regenerate it somehow.  Today we'll try the former.

There's quite a bit of precedent for dissolving away the eggshell protein (or at least, most of it) with a strong base, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), but specific recipes are hard to come by.  Several articles refer to this original gem, the most useful being this one, which allows us to deduce that those guys boiled their eggshells in a 2.5 wt% NaOH solution for 5 minutes, which easily removed the membrane and part of the protein matrix.  They then increased the lye concentration to 10 wt% and boiled for a long time, finding that all the protein that could be removed was gone by about 7 hours.  They didn't give a lye-to-eggshell ratio, though.  Additionally, this patent references another patent (we couldn't track down the original) claiming that boiling eggshells in 3 wt% NaOH would reduce the protein content of the shells to < 0.1%, although the boiling time and lye-to-eggshell ratio wasn't specified.

A protein content of < 0.1 wt% sounds good enough to us, so we decided to follow that route most closely.  Having to guess on the time and lye-to-eggshell ratio, we decided that if we had to boil for more than half an hour and use more than a 1:1 ratio, that it wouldn't be worth our trouble. (In that case, we'd just use Leigh's ash-based leavening instead!)  Alright, experiment planned; let's do this!

Here's our recipe: 15 g NaOH, dissolved in 500 g tap water, with 15 g coarse-ground eggshells (1-2 mm particles) added.   Boiled for 30 min.  Wear safety glasses and gloves until everything is neutralized later on (see below).

As the mixture simmered, the lye water turned a cloudy yellow.  A good sign that we're dissolving protein.

After boiling, we poured the liquid through a coffee filter (supported by a polypropylene funnel) into a quart jar.  The eggshells don't look that much different than before, except maybe slightly darker.  The pigment (they were brown shells) is still there.  The coffee filter is really slow, so something like an old t-shirt or terrycloth towel might be better.

The filtrate is still highly caustic, so be careful with it!  We wanted to neutralize it before doing anything else, so we added a couple tablespoons of our good ol' red cabbage pH indicator, causing the filtrate to go from yellow to slightly-darker-yellow.  Note if you're following along at home--dumping the filtrate down the drain without neutralizing might kill some of your friendly septic system bugs, so please neutralize!

Then we added vinegar until it turned green, then blue, then finally purple, indicating a neutral pH.  (We had to add a few more tablespoons of pH indicator as it got more and more dilute, because the color changes started to get hard to see.) Now it can go down the drain or into the compost.

The next step is to repeatedly rinse the boiled eggshells to wash all the lye off.  These are the rinses (plus pH indicator), showing steadily decreasing alkalinity.  After the fourth rinse (which was with vinegar), the filtrate is neutral, the eggshells should be substantially free of lye (and hopefully protein!), and we're good to move on (and take off our safety glasses and gloves).  We also neutralized the second and third filtrates with vinegar, too.  Safety note: working with lye on something you're planning to eat has the potential to cause some serious damage if you don't neutralize properly.  Be careful and only do this if you're comfortable with the chemistry! Also, make sure you're using pure lye, and not some cleaner that has lye combined with other chemicals.

Drying the lye-boiled eggshells makes them easier to work with. In the oven at 300 °F for 15-20 min ought to do the trick!

Time to make some experimental biscuits!  Five sets of three biscuits each.  Recipe per set: 0.5 cups all purpose flour, 0.25 teaspoon leavening, 0.125 (1/8) teaspoon salt, 1 tablespoon butter (in the bowls), 1 teaspoon apple cider vinegar plus milk (2%) to bring the volume up to 0.25 cups to make a faux buttermilk (in the glasses).  We processed the bowl contents in a food processor for about 5 seconds to cut in the butter, then added the "buttermilk" and processed for another 5 seconds to mix everything up, scooped the dough/batter into drop biscuits and baked at 400 °F for about 20 min.  The five sets differ only in their leavening: no leavening, lye-boiled coarse-ground eggshells, coarse-ground eggshells, fine-ground eggshells, and baking soda.

After baking, there' a clear difference between the No Leavening control and the rest, but also between the baking soda and the rest.  Between the eggshell sets, the lye-boiled and the finely-ground are about equal, and slightly more risen than the coarse-ground.  However, all the eggshell sets are very close to each other, and closer to the control than to the baking soda.  Also, we didn't have enough room for all fifteen biscuits on this sheet, so we baked the third biscuit of the last three sets separately.  Their appearance was consistent with the biscuits here.  Hooray for reproducibility!

The textures are consistent with the appearance, but it's hard to tell from the photos.  Also, the biscuits other than the baking soda set weren't cooked all the way through after 20 min.  We put them back in the oven; after another 15 minutes they were no longer doughy, but they didn't rise any more.  The flavor of all the sets is decent, so the control set and the eggshell sets would make decent dumplings if you're into that sort of thing.  Overall, the conclusion from these experiments is that the eggshells provide some leavening effect, but not much.  For us, the ground eggshells don't really get the job done, and it's definitely not worth the effort of boiling them in lye water to dissolve off the protein.

But we're not done with these experiments yet!  Stay tuned for Part 2, where we dissolve and regenerate the calcium carbonate part, and see how that works as leavening!

Syrup Update

Of the eight taps we have in our yard sugar bush, only a couple have been flowing significantly.  The Tree of Heaven, both Bradford pears, and one of the Siberian elms haven't even made a drip, the other elm has about a cup of sap, and the Lombardy poplar has about half a cup.  But the other two, the box elders, have been running like a gazelle.  By early Saturday morning, we had collected 38.4 lbs of sap, which means it was time to start boilin' it down!

First: a measurement.  Our sap is starting off at about 2.5 wt% sugar, according to our hydrometer. Not bad for a box elder, pretty much in line with a study from St. John's University in Minnesota.  But more importantly, with that number, we can calculate all sorts of expectations for this batch of syrup.  Allow us to momentarily digress!

This is the sugar content of the box elder sap on the Balling scale, which is essentially the same as the Brix scale more commonly used for sap measurements. (Using the same hydrometer we use for brewing wine.)

For example, knowing the wt% sugar, we can use the tables here to calculate the density of the sap and the resulting syrup (because syrup is normally 66 wt% sugar, which is very close to the solubility limit at room temperature), which will give us the volume of the sap and the resulting syrup, and our expected ratio.  Those calculations are detailed in this spreadsheet, if you want to plug in the numbers from your own sap. For us, our 38.4 lbs of sap at 2.5 wt% sugar works out to about 4.6 gallons, from which we should be able to expect just over two cups of finished syrup. (But note the caveat below.) 

38.4 lbs of sap at 2.5 wt% sugar should yield about 2.1 cups of syrup, which would be a ratio of 34.6:1.  That would be pretty good for a box elder.

We can also use other tables in that document to calculate what the boiling point of the finished syrup should be.  It would normally be 4 °C (7 °F) above the boiling point of pure water wherever we are, but that depends a little bit on what the boiling point of pure water is.  We're in the suburban Denver, where water boils at about 95 °C (203 °F) due to about 18% lower absolute atmospheric pressure. (Don't worry, we used NIST data for the Antoine equation to calculate the vapor pressure of water at that temperature, and everything checks out.  Well played, Universe.)  As it turns out, the difference in boiling point increase for syrup at our elevation is within the precision of our thermocouple reader.  Or, long story short, we're looking for a final temperature on our syrup of about 210 °F.  Time to light the fire!

We added a wind break to our Dakota Rocket Silo and started out using the widest-diameter pot we have.

As we started to build up a bed of embers, the air flow through the chimney part dropped off quite a bit, and we weren't getting much 'rocket' effect.  So, we widened out the pit, raked some of the coals to the back part, and added a second pot on top.  The direct contact of the pot on the coals got that pot boiling a lot faster than the one on top of the chimney, even when the rocket effect was strong.  Conductive heat transfer beats convective heat transfer (with air) every time!  If you go this route, though, be careful not to get ashes, etc. in the lower pot.

As a side note, if you're trying to use a lot of small-diameter wood (e.g., thumb-size branches from an unsightly, rabbit-attracting brush pile), breaking the sticks by hand might start to get old after the 50th or 60th one.  At that point, a loppers will become your best friend.

With the volume decreasing by about half, some of the minerals ("sugar sand") started to precipitate out.

Eventually, the volume got low enough to combine everything into one pot.  Time to make some pancakes!  We ended up adding one more layer of blocks back onto the wind break.

Pancakes done, sap still boiling.  We might have to modify our evaporator design for the next batch.  In the meantime, let's make bacon, too!

Bacon done, sap at ~35% sugar.  Daylight running out.  Time to bring it inside to finish on the stove.

And.....the finished product in a pint jar.  It's delicious.

Ok, so the finished product looks much closer to one cup in volume than the two we expected.  Why the difference? (Here's the caveat we mentioned above.)  There are a number of potential contributions.  The equations above are for solutions of sucrose in water, so the initial 2.5 wt% reading we took didn't account for other dissolved solids (e.g., the sugar sand that precipitated out during cooking).  That is, we might have started out with lower than 2.5 wt% sugar.  Also, there were some losses on transferring between buckets and pans, filtering, and what we took out for testing along the way.  We were also physically unable to resist trying some of the 35% stuff on the pancakes, which probably accounted for at least 1/4 cup (don't judge!).  Finally, we also ended up going a little bit over 66% sugar (closer to 70%, based on our honey refractometer's scale, which had store-bought maple syrup right at 66%), which would decrease the volume, in theory, by about another 1/6 cup.   Overall, even if we got one cup syrup instead of two, our sap-to-syrup volume ratio was still a respectable 70:1.  In general, it looks like the calculations above should get you to at least within a factor of two.

How is your syrup season going?

Butcher Block Counter From Reclaimed 2 x 4 Lumber

A few weeks ago, we mentioned that one of our main goals this year was to finish the butcher block counter (and corresponding cabinets) we built to give our kitchen some extra horizontal work space and culinary device storage capacity.  Finally, after more than a year of testing it in-place, we slapped some doors on it and put a water-resistant finish on the top.  There are a couple naggly things to finish up yet, like deciding whether we also want to finish the cabinet doors, but by and large, we think the project is ready for blog-reader eyes.

This is what it looked like a year ago.  We made the top out of reclaimed 2 x 4s (yep, pine!) that we planed clean and glued together.  The end-to-end length is about eight feet, so we made each row out of a six-footer and a two-footer, alternating the two-foot ends (i.e., one row was 6-2, the next was 2-6, and so on).  It's about 16 inches front to back. Despite our best efforts, there was a stretch in the middle where they didn't line up perfectly.  It took us about a year to acquire a belt sander, which made the job of blending the slabs tolerable.

We also needed the sawdust from sanding to make some wood putty, of which a significant amount was required to fill in all the imperfections in the wood.

For example, there were a lot of nail holes like these.

After filling with putty and sanding, the same holes looked like this.  There's a bit of discoloration around the nail holes yet, but they almost look like tiny knots.

Viewed from the angle of a typical adult human walking by, the now-filled holes look downright acceptable.  However, with a lot of board-to-board color variation like this, the sawdust used to make the putty doesn't actually match any of the wood colors perfectly.

Back in place in the kitchen, it's time to add some water resistant coating.  We could have maybe foregone the finish, but Jake does a lot of drooling when Katie's cooking.  Better not to risk it.

We used the Howard's butcher block conditioner, which is a mix of mineral oil, beeswax, and Carnauba wax.  It definitely enhanced the wood color and soaked in pretty quickly.

Finished top.  Katie approves.

There's a bit of a sheen to it, but not too bad.

Add some rustic-looking doors, and this thing is starting to get some personality!  Of course, if you build the doors while the top is off, they might not fit perfectly.

There, that's better.

Oh yeah, forgot to mention the shelves.  They're reclaimed pallet wood from the two best pallets we've ever acquired.  The top was hardwood (aspen, judging by the scent when cutting it), the bottom had some nice blue-stain pine.

Finally, seal the edge with some silicone caulk to prevent water from getting back there and to prevent potential admirers from noticing the uneven ends.

Done! (as long as we decide not to coat the doors...)

Non-Maple Syrups on Tap

It's tree-tapping season!  Since we're huge pancake lovers, we've been keen on tapping trees for quite a while.  Two potential problems, though, are that we live in suburban Denver (is there enough of a cold period to generate a significant sap flow?), and we've got exactly one maple tree in our yard, which isn't big enough to tap. (It's not even an actual sugar maple--it's a silver maple!)

We do, however, have several non-maple trees that are big enough.  And since the process is pretty much the same, we figured we'd tap what we've got and see what we get!  Several places note anecdotally (e.g., here) that other tree species can be tapped (with tempered expectations because the sugar content and/or sap volume is lower than for sugar maples), and some even talk about tapping coniferous trees!  But with few exceptions (mostly for other types of maples, birches, or walnuts), these sources don't give much in the way of what to expect in terms of yields or flavor.  Looks like a data gap waiting to be filled!  We ordered up a set of 10 taps from the internets, scored some free buckets from the local grocery store bakery, and set 'em up yesterday.

We went around the yard and measured tree circumferences at about chest height.  The diameter is the circumference divided by pi (d = c/π); and a general recommendation is to tap trees no smaller than 10 inches in diameter.  Looks like we've got two each of box elders, Bradford pears, Siberian elms, and Colorado blue spruces, along with a Lombardy poplar and an invasive Tree of Heaven that qualify.  We'll probably pass on the spruces this year.  The tapping process is not supposed to hurt the tree or affect its longevity, but the elms and the Tree of Heaven would surprise us if they lasted beyond this year anyway.

The buckets are 3.5 gallons and used to have "donut glaze" in them.  We washed them out in the bath tub, although if we had thought ahead a little, washing them outside with the hose last summer would have been a lot easier.

The taps came with two-foot sections of tubing attached, the ends of which we warmed up with hot water to make them easier to push onto the barbs of the taps.

We connected the tubing to the taps in the kitchen, before we went outside.

One last bit of prep (heh) was to add a duct tape stopper about 1.75" up the drill bit so we don't go too far into the tree.  We also drilled holes in the bucket lids; the tubing said 5/16", but it needed a hole a little larger than 3/8" to fit through.

First hole in the boxelder, and it started dripping immediately.  That's a good sign!

The two box elders that were big enough to tap are actually two trunks on the same tree.  It's also right on the property line, so we don't have access to the south side, which is the side most preferentially tapped.  The East side will have to do!

Here are the other three trees we tapped with out first five buckets.  None of them had sap running right away.  We scored three more buckets the next day, so the two elms and the other Bradford pear are next in line.  Woo hoo!  Visions of pancakes are dancing through our heads.

What kinds of trees are you tapping this year?