Ask the Alchemist #181

Level: Novice

Reading time: 4 minutes

Have you ever tried tempering chocolate with a Sous Vide? 

I tried making cocoa butter silk in the sous vide like you showed.  This look right to you?  I did not stir. Cool at room temp.


I’m really glad you dove in and tried making your own.  I’m going to be writing a full how to article with all the ins and outs, plus troubleshooting, what ifs and variations you can try.  In the mean time I’ll just answer questions here.

In short, I can’t tell if you have silk there or not. In the solid form, there is no visual clue whether it worked or not.  To be 100% sure you have to test it.


As a reminder, just finely grate up 1% silk and add it to melted chocolate that is at 94 F.  Stir it in well and let it set for 1-2 minutes.  Give it another stir to make sure the specks of silk are melted and incorporated, and pour it into your prepared molds.

Most likely though, if you followed the directions of putting the cocoa butter into the water bath at 92.5 F AND at the end it had a thick opaque look and texture, then that is the sign it worked.

It should look like this.

You can either stir it or not stir it.  It does not really matter. You won’t mess it up by stirring.  And really, I prefer stirring it to verify it is smooth and creamy throughout.  It is a little chunky I would tend to put it back in the water bath another couple hours, maybe bumping the temperature up 0.2 F.

Nice and simple today.

Happy tempering.


Fiji – a new Direct trade origin.

Let’s start off with saying this bean ranks in my top 10 favorites ever.  It has virtually everything I love about chocolate rolled into one.

Just look how it pegs the chocolate category in the spider graph!  And sweet.  And fruity. And nutty.  The flavors just keep coming and coming.

Yeah, I’m that impressed.


Direct trade from Fiji.  I have a feeling I could eat this chocolate all day long without tiring of it.   But not because it is boring.  It’s just so present and full of flavor and intensity.  I’m really loving this chocolate.  Raisins, creme brule, vanilla and macadamia nuts weave a lovely and complex dance throughout the flavor profile.

And what is more, it is a Forastero.  Very possibly the best Forastero I’ve ever had.

Get back here!  No walking away because it isn’t Criollo.

Forestero beans get a bad rap from the cocoa “experts” who have probably never tried one.  They’re a personal favorite of mine, and you know I’ve tried a few different beans in my time.  Foresteros, with good genetics and most importantly good fermentation and drying, can be wonderfully flavorful.  They’ may not be as bright as Criollo or as dynamically fruity as Trinitario, but what you get is a deep, rich chocolate flavor.

Go check it out.  Both Retail and Wholesale.

Ask the Alchemist #180

Level: Apprentice

Reading time: 8 minutes

Have you ever tried tempering chocolate with a Sous Vide? 


Yes, I have.   In theory it seems like it should work perfect.  Super stable temperature settings.  A warm insulating water bath.  Hands off controls.   For those not familiar, this is an example of one.


It is basically a circulating water heater with both accurate and precise temperature control.  And can help you make utterly killer rare steak!


Unfortunately, in practice, it is rather inconvenient and downright causes problems in other ways with chocolate tempering.

But there are other uses for it chocolate making and I’ll explain those later one.

What went wrong?

Well, first off it is a water bath and working with it and chocolate together rather feels like working with a live electrical line.  If you are good and know what you are doing, you are mostly safe, but…..chocolate – water.  Rarely a good mix.

After getting over the fact that I could not seize my chocolate with the water present,  the main thing was that it took way too long to melt the chocolate.  It took 2 hours for me to melt 2 lbs of chocolate to 95 F.  The main issue was the water was 95 F.  And with the chocolate being  just a bit cooler at 75 F, the flow of heat is very slow.

Sure, I both could have mixed it by hand and turned up the heat, but in that case, there was no reason not to just get a bowl from the cupboard and melt the chocolate over a pot of hot water.  Either way I was controlling the heat myself and stirring manually.

After a couple hours, and some hand kneading (pst, don’t tell, but I turned it up to 98 F too) the chocolate was finally melted and flowing.   I considered tossing in a bit of seed but realized I had no good way to get it mixed 100% well and also had not good way to get it out of the bag it was in without both making a mess and causing so much edge sheer that I had a lot of bloom.

I settled on cutting the bottom edge off the bag and squeezing it out like frosting from a piping bag.  That worked well enough except for the loss of a perfectly good bag.  I then mixed in my seed and proceeded as normal.

I shudder to imaging if I had to temper 5-6 lbs of chocolate this way.  A sous vide may have great temperature control but the drawbacks are too severe for routine use of tempering your bulk chocolate.

Recall though I said there was another great use for a sous vide?

That use is making cocoa butter Silk.

What is Silk you ask?  I tossed out a Twitter poll  the other day (go vote, a couple hours left), and granted the response rate was low, over half the responders didn’t know what Silk was.

Silk is great and amazing and what you should be tempering your chocolate with.  I’ll tell you how to use it in a moment.

In short, it is really nothing more than tempered cocoa butter.

Some time ago I reviewed the EZTemper.  Its sole purpose is to create cocoa butter Silk.  It is basically an air incubator.   It holds your cocoa butter at 92.5 F where over the span of 24 hours crystallizes into extra hardy, super aggressive Type V seeding crystals.  Oh, and is like silky thick buttercream when you pull it out, hence the name.

It goes from this:


To this:


Note how it is opaque and thick.  Melted cocoa butter is clear.  That opaqueness at the right temperature (92.5 F) is the sign of successful Silk.

And a sous vide is nothing more than a water incubator.  You can set it for 92.5 F (or 122 F and make great steaks!!), put in a sealed jar (get rid of that plastic bag) of chopped up cocoa butter and come back 24 hours later to Silk.

What do you do with it?  You temper with it.  And it goes like this.

1)            Melt your chocolate to 92.5 or 94 F*

2)            Stir in 1% by weight Silk

3)            Pour your Silk seeded chocolate into your molds.


You will probably notice that you are tempering at a much higher than normal temperature.  This is because the Silk is pure seed crystal.  It gives a great scaffolding upon which the chocolate’s cocoa butter can and will crystalize around so the temperature can be hotter.  Being warmer also means the chocolate will be less viscous and so has less edge sheer, so inadvertent edge bloom is reduced.

*Oh, that range of temperature.  You can allow your Silk to set up.  If you do that, then you want your chocolate at 94 F so that it can melt the Silk and end up at about 92.5 F.  If you are using it fresh from the water bath and it is still creamy, then it’s at 92.5 and so you add it to chocolate at 92.5.

And a couple other things I discovered.  You can seed other cocoa butter and shorten your 24 hour incubation time.  I had one batch of cocoa butter that fully melted (I’ll be writing a full how-to of Silk making and will address this) so I added about 10% Silk to it and left it to incubate at 92.5 F for about 1 hour.  The seed propagated and made more Silk quickly and I’ve successfully tempered a couple batches of chocolate with it.  It may turn out that theory and practice will part company at some point, but in theory I cannot come up with any reason you could not continuous re-seed cocoa butter to make new Silk over and over in less than 24 hours.

So, with all that in mind, go get yourself a Sansaire Sous Vide.  I can’t recommend it enough.


And if you don’t want to do that, let me know either by email or comments below if you would be interested in purchasing a little Silk. I’m thinking of offering it over the winter months.


Ask the Alchemist #179

Level: Novice

Reading time: 4 minutes

I was just wondering, how important is a melanger is for this recipe of white chocolate? I know it’s important for grinding regular chocolate, to smooth the texture of the cocoa solids – but does separated cocoa butter need the same grinding, or is it already quite smooth? I’m sure it’s both useful and convenient, but I was curious if it is indispensable to this recipe or how much of a difference it would make to try making white chocolate without one.

If the use of the santha grinder in this recipe is grinding the powdery ingredients (sugar, milk powder, soy lecithin) into the cocoa butter, could pre-grinding those ingredients very fine (say, to maybe a powdered sugar texture) make a good white chocolate without needing the santha grinder?


A melanger is indispensable for any chocolate be it dark, milk or white as long as you are defining chocolate as modern chocolate with a smooth and silky texture.

Cocoa butter doesn’t need further grinding by a melanger, but everything else you add does.

Nothing available by the home chocolate maker can get chocolate as smooth as a melanger.  I’ve tried everything I could think of and they all fail to do the job.

The reason has to do with the vague term “fine” or “very fine”.  Those just fail to mean much of anything.  Sure, powdered sugar is fine compared to corn meal, but both are coarse compared to the particle size of the sugar once it has been refined in the melanger.

And that is worth noting.  It isn’t just, or even primarily, the cocoa solids that are getting refined down.  It is the sugar and milk powder.  Let’s get away from ‘fine’.

The sugar and any other solids in chocolate are in the 10-15 micron range.  That is 1/100 of a millimeter.  In contrast, granular sugar is somewhere around 500 um( microns).  Fine castor sugar can get down to half of that.   Now, if you go searching around you will find that 10x superfine sugar can reach 15 um.  Home free right?  Unfortunately not.

Commercial powdered sugar contains cornstarch and/or other anti-caking ingredients which can lead to a gummy chocolate.  As for powdering your own, I just tried it.  I was able to get down as low as 25 um, but there were still some pieces larger than 50 um.  And that size will be coarse in your mouth.

I even tried filtering it through a sieve, and what came out was in the 10-15 um range.  The problem though was that I could only get about 10% of the sugar through (less than 1 oz) before it started clogging and caking (hence the anti-caking in powdered sugar).

Really, it isn’t a viable method for anything more than just a couple ounces of chocolate.

Finally, that neglects the aeration and minor conching that occurs in the Melanger.  Non-refined white chocolate has to my tastes this odd, harsh taste  that goes away over the 12-18 hours needed to make white chocolate in your Melanger.

There you go.  There is no making modern chocolate without a Melanger at the minimum.


Ask the Alchemist #178

Level: Alchemist

Reading time: 20 minutes (if you are lucky)

Question: Time?
Things are considered tempered when you take a test strip cool it and it has the characteristics you want. My question is does this happen rapidly, say 95% of the fat is in “V” at 10 mins, or is “tempering” when say 50% of the crystals are in the correct form. Does extending the time at temperature to say a day or 2 get significantly closer to 100% in V? Does this make a difference? You probably reach a point of diminishing returns, just curious how much science has been applied to this voodoo…

Funny you should mention voodoo.  As I am going to take this into the exact opposite direction and define tempering in technical terms.

It’s worth noting that as I think of all I want to convey I feel like the philosopher who has attained enlightenment from the study of a butterfly wing and now wants to convey it to everyone….and takes page after page explaining it and ultimately fails because you usually can’t explain deep concepts quickly or easily.   Regardless….onward.

Chocolate is tempered properly when the inflection point of the of a temperature vs time cooling plot has a slope of zero.

And I suspect that doesn’t mean or explain anything to most of you.  If you have a look around the internet you will find this old school image pretty quickly.

old cooling curve

Digging a bit deeper and you can find something like this that shows real data in a form more of you can relate to.

modern cooling curves

In both cases they are showing plots of chocolate in different stages of temper, from untempered all the way to over tempered.

And I want you to read that last line again.  There is something very important there that takes many people many years to realize.  The first epiphany as it were.  Over tempered.  Chocolate can be over tempered.  Understandably a large number of people think you want 100% temper.  All Type V crystals.  But that isn’t the case.  You want a balance.

So that answers a part of your question.  Or more to the point, it sheds some light on some of the assumptions you have made about tempering.  That it is an end state.  Sort of like absolute zero.  And maybe it is. The key here is understanding that IF the perfect temper is analogous to absolute zero, then your goal is NOT absolute zero, but some temperature above that.

Try and let that sink in.  I’ll try and explain why that is at the end.

But before we get deep into all the revelations that those plots can give us, let’s take a few moments and talk about what you are seeing there.


Pretty much all of tempering is predicated on the concept of crystallization.

The following concept is one you need to wrap your head around.

Solidifying fat crystals give off heat in the same way dissolving salt crystals take in heat.   These are the two sides of the same coin or concept.

That doesn’t make sense?  This puts it into tangible terms.

If you make ice cream the old fashion way, you will recall you mix ice with salt.  Remember that?  Do you know why?  Solid salt is just sitting there.  It has low energy.  Salt in solution is moving around.  It has more energy.  That energy has to come from somewhere.  In the case of your ice cream and ice, it comes from the temperature of the system.  Ice cream, ice and salt separate are all at 32 F.  If the salt needs energy to dissolve, then it has to steal it from somewhere so it takes it from the only place it can; the temperature of the ice cream and ice.  The result is that those temperatures drop to something under 32 F as the salt dissolves and your ice cream solidifies.

Got that?  The whole point is to melt a crystal it has to take in heat.  Therefore the opposite is also true.  To form a crystal, heat is given off.   This heat is called the heat of crystallization.  To go all science and geeky on you:

“Heat of crystallization or enthalpy of crystallization is the heat evolved or absorbed when one mole of given substance crystallizes from a saturated solution of the same substance.”

Let’s bring this back to chocolate and set the stage.  You are in the process of tempering your chocolate.  You have either made or introduced seed to your untempered chocolate.  For the sake of discussion, let’s call it 31 F.  You pour it up into your mold and it starts to cool and eventually set up.

If we peek behind the curtain, and can monitor the temperature and crystals we are going to see the temperature start to drop.  That is just the natural cooling of the chocolate.  Energy is being given off to the atmosphere or maybe your refrigerator.  At the same time, the seed of Type V crystals are going to start propagating or growing.

And now the fun part (did I mention I’m a retired chemist who finds this fun?).

We can make a prediction.  As the crystals start to form we know (see above) that they are going to start giving off heat to the surround chocolate.  And what is that going to do?

Very good.  The temperature is going to rise.

And if we record those temperatures and the time, and then plot them, what is it going to look like?  It is going to be a decreasing line (the temperature is falling initially because it is in the refrigerator or whatever) then,  (oh, I’m so excited) since those crystals are giving off heat, (I’m virtually giddy here) the line is going to level off or maybe (shaking with geek excitement) even go back up!  Then, once all the crystals are formed and no more heat is being evolved (yep, pulled in a science word there) the temperature will continue to drop to whatever the ambient temperature is.

Do you have that image in your head?  Hopefully, it looks a LOT like this:

predicted cooling

Which, wow, looks pretty much identical to the plot at the beginning for properly tempered chocolate!

Science!!! (giddy again….calming down…. )

Okay, I’ve calmed down for the moment.  Hopefully you have the concepts down and we can talk about what they mean.

The first thing I want to address is that a zero slope (that flat spot) is nothing special.  It is empirical meaning that it is just lucky coincidence that the majority of we humans like our chocolate when it is tempered at a zero inflection.

If you go back to the top and have a look at the curve of untempered chocolate you will notice it is basically a straight line pointing down.

“But alchemist, even bloomed chocolate has crystals.  Type III, IV and V.  Don’t they have a heat of crystallization and wouldn’t they cause some heat rise?”

I am proud of you for making that connection.  It is 100% true.  IF…and this is where I didn’t play straight with you…we were truly measuring the temperature of your chocolate as it set up.  But that is not what those plots are from.  They are actually from a special setup that measures the degree of temper in a chocolate.  It basically looks like this:

Temper setup

This image and the text below on It’s workings is from Ticor systems

“Their operation is quite simple. A cup-like opening at one end of a long metallic (copper) tube is filled with a chocolate sample. The other end of the tube is inserted in a mixture of ice and water held in an insulated container. A temperature probe (thermocouple in early versions) is then inserted into the chocolate. Since the chocolate sample is above 85°F and the sample holder is attempting to reach the temperature of the ice bath (a questionable 32°F), the chocolate gives up heat to the holder and is cooled to solidification.”

The key difference here is the ice bath and that in a degree of temper analysis you are forcing the chocolate and temperature down quickly along a reproducible path (because is a constant temperature and the system is insulated).  The consequence of this is that you can see deviations easily and you are literally forcing the chocolate to solidify without crystallizing.  Because no crystallization is happening, no heat is given off and no rise in temperature is noted.

Got it?  Good!

And now we can talk about some of those bits of enlightenment that fall out of these graphs.

If you look at the 2nd graph above with all the overlaid plots you see a spectrum of non-tempered curves all the way to over tempered.  This means tempering is a continuum and what falls out of that is that tempering is not a discrete state but a process and because we can have a full range of tempers we can have variables that we can adjust in a predictable manner to give us those final degrees of temper.

What are those variables?  Well one big one should be obvious.  The amount of Type V seed you have present and the original question hints at that.  And that makes sense.  The more seed you have, the more energy that is given off in a set amount of time and the more the cool curve tips up.  Likewise, if you don’t have enough, it doesn’t tip up enough, the slope of the line doesn’t make it to zero, and you have under tempered chocolate, and if it is under tempered too much, it can bloom.

So, is time something you can manipulate?   Will more time (2 days?) give you a higher degree of temper because more seed is formed?   It certainly seems like it might be, and it can be, but it turns out that it isn’t practical.  And the key is understanding that time is only helpful if it is your only variable.  And in many cases it isn’t.

If you are tempering from scratch it is useless.  Why?  Because when you bring your chocolate down to 80 F or so and form seed, how much you form is varies with how fast you reduce the temperature and the ambient temperature.  Without being able to control those exactly, you will have different amounts of seed (which you have no way of knowing) and that basically means you are starting from a different point in the tempering process each time so you can’t get to the degree of temper by measuring time.

If that isn’t clear, think of it as getting a car up to 60 mph (perfect temper, zero slope inflection)  from a random unknown speed with only a stopwatch. It can’t be done.  There are too many variables.  How fast are you going (how much seed initially), how much are you accelerating and how do you measure it (what is the ambient temperature) and are there hills that you have to go up or down (how much heat loss do you have).

This is why hand tempering can be a series of failures until you both get a feel for how fast 60 mph is and you get used to the road (i.e. your techniques and conditions get VERY reproducible).

So what are you to do?  You use some form of seed.  And a tempering machine or water baths if you can.  Neither is magical.  They are nothing more and nothing less than variable control and management.

When you use seed or silk you starting with a known amount of seed, and better yet (analogy shift warning) your speed IS 60 mph and you just have to maintain it by watching the speedometer (your temperature).

If you want a lower degree of temper, you use less seed/silk.  If you want I higher degree of temper, you use more.   That simple.

So, it was probably hard to miss that I mentioned both seed and silk.  The distinction is that the former is tempered chocolate and the latter is tempered  cocoa butter.  And they produce different tempers.  Not just different degrees of temper, but actually different types of temper.

S. Beckett (The Science of Chocolate) notes this:

The temperature at which the inflection on the curve occurs is very important.  The higher the temperature the more mature the crystallization and the higher the temperature at which the chocolate can be used for moulding and enrobing.

Silk makes for a more mature crystallization and is my personal favorite way to temper (video of that coming up).  You can see this by how it is used.  You mix it in at around 93-94 F.  You use significantly less (0.5-1%) than you would tempered chocolate (20-30% many people recommend) and it propagates very fast through the chocolate, setting up quickly and with a particularly high resistance to blooming.  And if you were to run a cooling curve on it you would see it produces the inflection point at a higher temperature correlating with a more mature crystal.

Is this all helpful day to day?  I personally think it is since I wrote it.  How?  I think 90% of the help it gives is taking some of the mystery out of tempering (after you reread it a few times).  It is just variables and if you grasp that, you can start to look for variables in your process and eliminate them or at least identify them when something goes awry and you chocolate blooms.

Can your or should you set up your own temper meter?  If you find it fun and like the hard data, by all means do it.  It isn’t hard.  It is basically a thermometer and an insulated ice bath.  You will probably have to play around a little with your sample size to get a flat line for untempered chocolate but that is about it.  But of course you don’t have to.  Hell, I LOVE this stuff and have not done it. But you can.

Oh, one more thing.

Remember I said I would explain why you don’t want an absolute temper?  It’s really kind of simple. Mostly it is because you are a person eating chocolate and not a chemist striving for a perfect beautiful crystal.  You are not looking for perfection in structure.  You are looking for perfection in mouth feel.  You are looking for an experience.  You are looking for that perfect state where the chocolate is smooth and melts easily in your mouth.  That point of state that allows maximum release of flavor and enjoyment.  You are looking for the perfect tipping point where it is almost bloomed and almost too hard.

You are looking for balance.

I hope that was enough science to this voodoo we call tempering.

Welcome to the art AND science of chocolate making.

Ask the Alchemist #177

Level: Alchemist

Reading time: 13 min

Hi, John – I just watched your roasting video. I am one of those people (for the last 1.5 years since I moved to Seattle) who doesn’t currently have an oven. I hope to move in the next few months, but until then I’ve been taking my beans to my son’s house to roast them in his oven. After watching this video, I’d like your opinion.

The oven is a Wisco – 1300 Watts.

Somehow I made the assumption that using this for my beans wouldn’t be a good idea because the air circulation is so strong inside it; much stronger than a traditional convection oven. When using it for typical baking I need to drop the temp about 25* from what recipes recommend. Now I’m not so sure. This thing is small – about 15in wide, so these are the Pyrex dishes I have that will fit. Of course, I don’t want to take a chance on wrecking a batch of beans. Given what I’ve described, do you see any problem using this for cacao?


Let us get this out of the way early.

I am going to lie to you today.

That is a lie.

What I mean by that is that in a binary world, something is either the truth or a lie, and if I am not telling you the whole truth, I therefore must be lying to you.

This is basically I joke I tell to get the attention of a group of 8th graders when I talk about the science of chocolate making.  Go watch my youtube video ( ) where I tell the whole story.  Suffice it to say, I am NOT going to actually lie to you (on purpose) but I am going to leave a lot out since what I am going to talk about is full of maths and thermodynamics that are going to make many people’s eyes glaze over.  My goal is to get you to understand what is basically going on and why I am making the statements and assertions I make.


And it’s very possible many of you CAN handle the truth.

With that, hold tight, and let’s jump in.


First the answer.  Yes, you can use that oven.  For 1 to 2 lbs of beans.

Now I will tell you why I say that.  But I need you to be somewhat conversant in some basic terms and how I think.

From Google – “The British thermal unit (BTU or Btu) is a traditional unit of work equal to about 1055 joules. It is the amount of work needed to raise the temperature of one pound of water by one degree Fahrenheit.”

I am starting there because I know from empirical experience that my Royal #5 coffee roaster produces about 42000 btu/hour with propane.  How do I know that?  I measured the orifice of the propane outlet and looked up the BTU/hour connected to standard liquid propane.

Multiplying that out, that translates to 44310000 joules/hour.

I can roast 35 lbs in my Royal in about 20 minutes or one third of an hour.  That means I need  14770000 joules of energy for 35 lbs regardless of time it takes me to get it there.  Dividing by 35, that means 422000 joules per pound are required.

Part of this kind of number crunching is verifying I am in the ballpark.  I’m going to do that with checking my pre-heat requirements against how long I know it takes me to pre-heat my roaster.

Iron has a specific heat capacity of 0.45 j/g C.

I know my roaster weights about 300 lbs, but estimate the portion I heat up to 350 F is only about one third of it or 100 lbs.

100 lbs = 45 kg iron =45000 grams

350 F is a change in temperature of about 150 C.

0.45 x 45000 x 150 = 3037500 joules to pre-heat.  If I divide by the heat input (44310000 j/hr) and convert to minutes (multiply by 60)

3037500/44310000 * 60 = 4.11

4.1 minutes to pre-heat.  Yep, that is not a lie.  Some days it’s a touch longer, but it’s in the ballpark, so I am counting that as confirmation that my heat input and roasting requirements are about right.

Next, we can use those numbers to see what a 1300 watt convection oven should be able to do.  But we need to get everything in the same unit.

Again, from Google:

“One watt of power converted to joule per second equals to 1.00 J/s. How many joules per second of power are in 1 watt? The answer is: The change of 1 W ( watt ) unit of power measure equals = to 1.00 J/s ( joule per second ) as the equivalent measure for the same power type.”

That just means that 1300 watts = 1300 j/s

We know we need   422000 j/lb.  A little quick math canceling out joules and the minimum time needed in seconds falls out.

422000/1300 = 324.7 seconds.

Dividing by 60 seconds/min tells up how many minutes we need to roast a pound with perfect efficiency.

5.4 minutes per pound.

On the surface, that sounds great.  Except you really don’t want to roast that fast.  If you try, you are going to over roast the outside and under roast the interior.  So you need a slower roast.  No faster than 12 minutes for a roast is what my experience tells me.  But you don’t want to turn the heat down and not use the oven to its capability so that means you should put in more than 1 lb of beans.  How much?  Just divide 12 by the 5.4 minutes for a reasonable estimate.

12/5.4 = 2.22 lbs = 1 kg

Which amazingly enough is right what I said at the top of the article.

“First the answer.  Yes, you can use that oven.  For 1 to 2 lbs of beans.  “

But you will note I said 1-2 lbs.  Why 1 lb?

Well, that delves into modes of heat transfer.  That means when you add heat to a system, there are three ways for it to get from the source to the item you want to heat up.

Convection, conduction and radiation.

This is a convection oven.  That basically means air heating up by the heat source, circulating to the air to what you are roasting and that heat transfers to the cool items (cocoa beans).   It’s pretty efficient since hot air can surround the beans except where it is touch the pan or other beans.  In a thin layer (what I advocate, and why I advocate it) 70-80% of the surface of the bean can be exposed to the hot air.

Conduction happens with contact.  From the surface the beans are on to the beans.  It’s actually pretty inefficient for anything that isn’t perfect flat.  In the case of a cocoa bean, there is probably only 10-20% of the bean touching the surface of the pan.  That is why it doesn’t do well.

Radiation is basically direct line of sight.  When the sun comes out and shines on your skin and you feel warm, that is radiation.  You are not touching the sun and it isn’t because it caused air to move and warm you.  So if there are elements shining on the beans from above, then they are being heated that way too.  If they are heating from the bottom, then very little radiative heating is happening.  Instead the elements are heating the pan and the pan is conducting the heat (per conduction – above) and heating the beans.  In this case, it’s probably the least efficient way to heat.

Ok, deep calming breath.  I know that was a lot.  We are almost done.  And I can now use those terms to talk in a more efficient manner about why you might only be able to roast 1 pound.

Even though this is a convection oven it doesn’t mean it is efficient convection or convection as good as it can be.  Also, conduction is going to be very low due to the very low percentage of bean surface area actually touching the pan.  And where radiative heat might be effective in some cases, the convection in a way circumvents it by distributing the heat around the chamber.  In this case though, that is not a terrible thing and is actually pretty good or the top of the beans might get scorched.

After all is said and done there is probably only 50-60% efficiency going on here.  The rest of the energy is being lost.  Either through the non-insulated walls and glass door or through direct energy loss when you open up the door to stir the beans every 5 minutes or so.  Remember, you still have to stir. If you don’t, the top of the beans will be over roasted and the underside that is in contact with the pan will be under roasted.

And how do I know so much is being lost?  Again experience and puzzle solving.

Years ago I had a drum roaster that I built.  Over time I modified it for efficiency.   It started off at 2000 watts, with a slow 6 rpm motor and no insulation.

If we do the same calculations, recalling we need 422000 joules per pound  and have 2000 watts we find we, in theory, could roast  a pound of beans in 3.5 min.

422000 / 2000 * 60 = 3.5 min/lb.

The drum contained 5.5 lbs of beans.  So if this roaster was working as well as my Royal, I can apply this math:

3.5 (min/lb) x 5.5 (lb) = 19.25 min

And predict it should have taken me a touch over 19 minutes to roast 5.5 lbs of bean.  But the reality of the situation was that I could only roast about 3.5 lbs of beans in that time.  Doing that efficiency check :

3.5 lb / 5.5 lb = 63.6%

This showed me my system was inefficient.   A little over 35%.

It was not until my 6 rpm motor died and I replaced it with a 45 rpm motor did I discover how important REAL convection is.  As soon as I did it, my roast time dropped to 14 minutes. It was like a 35% boost in power.  Efficiency really.   Consequently I was able to add more beans to my roaster.  When I put in 5.5 lbs, my roast time went back to 19-20 minutes – exactly where a good efficient system should be.

See, it was not enough that the beans were tumbling.  Too many were touching and protecting each other from the heat.  Just like in a table top convection oven with beans on a try.  It was not until I got them lofting did real, full convection kick in.  And it is worth noting that after I insulated my roaster, the roast time dropped to about 17 minutes showing again how much heat gets wasted out the walls and over time.  Just like when you open the door to stir.

So, sure, it is a convection oven, but the beans are only partly benefiting from the moving air.  Sure, if it was not convection, then the roast times would go way out to 30 minutes like a classic oven.    But you really can’t have too much convection in a non-tumbling roasting situation.

That is where I get the 50% efficiency count from.  30% or so from non-ideal convection (no loft) and 20% loss from continuously having to open the oven to stir and there you go.

A bunch of lies.  Well, half truths of omission.  And it was STILL a ton of reading.

Yes, you can use that oven.  For 1 to 2 lbs of beans.

And  now , hopefully, you know why and how to work it out yourself if you need.

Go have some chocolate.  You deserve it.



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