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Building a Vanilla Sweat Box

This arti­cle is an addi­tion to the 2‑part How to Cure Vanilla Beans article. 

A crit­i­cal stage in the cur­ing of vanil­la is the “sweat,” where the enzy­mat­ic process that devel­ops the vanillin takes place. The sweat box cre­ates an envi­ron­ment that holds the beans at the opti­mal tem­per­a­ture for this process.

In the How to Cure Vanilla Beans arti­cle, I describe how to put togeth­er an ad hoc sweat box using a cool­er and hot water bot­tles. In this arti­cle, I will describe how I built the elec­tri­cal­ly heat­ed sweat box used to han­dle larg­er quan­ti­ties of vanil­la pods.

Not Just for Vanilla

For the fer­men­ta­tion do-it-your­selfer, a box like this has many uses. Basically, what this is is an incu­ba­tor. You can set it up to hold any tem­per­a­ture above ambi­ent, so any process that requires a con­stant warm tem­per­a­ture is some­thing this box will be use­ful for.

In our house, this box gets used a lot for fer­ment­ing cacao. We have a few cacao trees, so we’re often fer­ment­ing small batch­es of beans for our own use. You could also use this box for mak­ing tem­peh or yogurt.

A Brief Disclaimer

I am not a licensed elec­tri­cian, the build instruc­tions I pro­vide here are offered on an at-your-own-risk basis if you decide to fol­low them. I’ve been using a box of this design, with the same elec­tron­ics I describe for 4 years with no prob­lems. My expe­ri­ence is that this is a safe design. Be aware of the risks of elec­tri­cal shock and fire that are always present with a project like this.

This is a very detailed arti­cle, there’s a lot of instruc­tions to fol­low. I strong­ly urge you to read it over first so you under­stand what you’re pos­si­bly get­ting your­self in to. There are a num­ber of things in the project that can be or need to be impro­vised, so going over the arti­cle will help you get some ideas for what might work using stuff you may have just lying around.

Stuff You’ll Need to Get Started

The sweat box has 3 main com­po­nents: the box itself, a rack for hold­ing the beans, and the ther­mo­sta­t­i­cal­ly-con­trolled heater.

The Box

For the box, I used a 50-quart Igloo MaxCold cool­er. This cool­er is the per­fect size, and it’s well insu­lat­ed. That will run you about $60 new, but I just used an old one I had sit­ting around. A trip to the thrift store is prob­a­bly a good way to get a cheap one.

The inter­nal dimen­sions are about 20″ x 10″ x 11″ deep, in case you’re look­ing for a sim­i­lar-sized sub­sti­tute. It’s no big deal to make a small­er one, we had a 25-quart one for a while at first.

The Rack

The almost-fin­ished rack on the workbench

The pur­pose of what I am call­ing the rack is to hold the beans away from the heat­ing ele­ments and allow air to cir­cu­late around the beans. The heat­ing ele­ments are hot enough (about 200℉) to burn if touched or melt plas­tic bags, so you will want to make sure there is some kind of bar­ri­er between the heater and the stuff you’re keep­ing warm.

Air cir­cu­la­tion helps the whole set­up be more effi­cient and pre­vents cold pockets.

I don’t go into a lot of detail on how I built the rack, it’s made out of stock alu­minum of the kind eas­i­ly found in a hard­ware store. It’s fas­tened togeth­er with pop riv­ets. I don’t real­ly expect you to go to this much trouble…you can, with some imag­i­na­tion, come up with a ready-made alter­na­tive. A plas­tic rec­tan­gu­lar stor­age bas­ket that you can find in a hard­ware store, for example.

Anything that fits into the box and keeps the beans away from the heat­ing ele­ment while allow­ing air cir­cu­la­tion will work fine. The size you’re look­ing for is about 15″ x 9 1/2″ x 10″ deep or smaller.

The Heater

This is undoubt­ed­ly the most com­plex part of the whole thing, and maybe a lit­tle daunt­ing for those who haven’t worked with elec­tron­ics before, but I’ll try to make it clear how it all goes together.

These are the parts you’ll need to build the heater (these link to a prod­uct page so you can see exact­ly what it is and pos­si­bly where to get it):

The exten­sion cords can be sal­vaged from broken/unused elec­tri­cal items: this is what I have done. The pop­si­cle sticks/tongue depres­sors are to pro­vide a thin insu­la­tor for mount­ing things that might get warm.

For tools, you’ll need a sharp util­i­ty knife, wire cut­ter and wire strip­per, and a pow­er drill with 3/8″ and 1/8″ bits.

The Container

this is a 6″ x 6″ x 4″ con­tain­er I got at a dis­count store

The plas­tic food con­tain­er is going to be our elec­tron­ic project box. The con­tain­er needs to have inter­nal dimen­sions of at least 5″ x 5″ x 4″ deep. The kind I like have snap-on sides to the lid, but any one with a secure top will do. Don’t try to use a “dis­pos­able” one, you need the heav­ier weight ones.

What we’re going to do first is drill a hole on one side of the con­tain­er, and 2 on the oppo­site side. These will be for the pow­er cord, the heater cable, and the tem­per­a­ture probe. On the 3rd side, we need to drill 2 1/8″ holes, 2″ apart for mount­ing the relay.

drilling dia­gram for the container
detail of the con­troller mount­ed into the lid of the container

On the lid of the con­tain­er, we’re going to cut a 1 3/4″ x 1 3/4″ square hole for the con­troller. Use the bot­tom of the con­troller mod­ule to draw the square on the lid with a sharpie and then cut it out with the util­i­ty knife. Use light pres­sure with mul­ti­ple pass­es to safe­ly and accu­rate­ly cut through the plas­tic. Be sure to cut on the inside of the line you drew, you don’t want the hole too big! A met­al straight edge is not a bad idea here.

Unbox the con­troller unit and insert it into the square hole so the face is on the out­side. There are two plas­tic spring clips to hold it in place.

Wiring it Up

OK, you have your con­tain­er drilled and the con­troller unit is mount­ed into the lid. Next, we wire it up. This first dia­gram gives you a big-pic­ture view of how the whole thing is wired up, so you know where all this is going.

General dia­gram of the con­trol box con­nect­ed to the cooler

Wiring the Control Box

Start by cut­ting an 12″ piece of wire off the 6′ exten­sion cord. Cut the recep­ta­cle end off, you won’t be using it.

In the wiring dia­gram (brown wire), this is the wire that con­nects the con­troller to the con­trol inputs on the relay. Split and strip the ends and con­sult­ing the cir­cuit dia­gram to see which ter­mi­nals to use, con­nect the con­troller to the relay.

Controller Box Wiring Diagram

Now thread the ther­mo­cou­ple tem­per­a­ture probe wire through it’s hole in the side of the con­tain­er. Connect the probe to the con­troller accord­ing to the cir­cuit dia­gram below.

Wiring in the Heater Power

To wire in the pow­er, take the 10′ out­door exten­sion cord and cut it so that the plug (male) end has 7′ of cord (for the pow­er cord) and the recep­ta­cle (female) end has the remain­ing 3′ of cord…this is your heater cord.

Using the util­i­ty knife, care­ful­ly strip off about 10″ of the out­er sheath of the end of each cord to expose the wires inside. Avoid cut­ting into the wires when strip­ping off the out­er sheath. How I do this is I set the util­i­ty blade to just bare­ly pro­trude from the han­dle, then make a cut along the length of the sheath, cut­ting just deep enough to go through it. Peel it back and cut it off.

Take the heater cord and cut about 6″ off of both wires, leav­ing 4″ of wire on the cord. This will give you the 2 wires you need to con­nect the pow­er to the con­troller unit.

Thread the pow­er cord and the heater cord through their respec­tive holes in the con­tain­er. Use the wire strip­per to strip 1/2″ of insu­la­tion off all the wires you just exposed, then use the wiring dia­gram and cir­cuit dia­gram to con­nect every­thing togeth­er. When insert­ing wires into the ter­mi­nals, take care to get all the wire strands into the ter­mi­nal. Use the wire nuts to con­nect the pow­er to the con­troller unit as shown in the wiring dia­gram. Pull on all the wires you just con­nect­ed to make sure they are not going to come out. Note: the pow­er con­nec­tions to the relay switch are not polar­ized, so it does­n’t mat­ter which ter­mi­nals you use.

Once you’ve got it wired, dou­ble-check all the con­nec­tions against the cir­cuit diagram. 

Using zip ties, anchor the 3 cords that go through holes in the con­tain­er: dou­ble-wrap and cinch a zip tie around the cord on the inside of the con­tain­er right where it goes through the hole. This is to keep some­thing pulling on the cord on the out­side from pulling on any­thing on the inside. The zip tie should pre­vent the cord from pulling out.

The Circuit Diagram

Mounting the Relay

The relay is mount­ed to the side of the con­tain­er. The pop­si­cle sticks (or tongue depres­sors) are used to pro­vide an insu­lat­ing pad between the relay’s met­al bot­tom and the side of the container.

The relay will build up some warmth, but not a lot, cer­tain­ly not enough to ignite wood. The wood keeps the plas­tic from pos­si­bly melting.

Cut the wood down to the width of the relay. Place the wood on the side of the con­tain­er, between the holes, then put the relay on top of that, lin­ing up the holes. If the wood cov­ers the holes, drill through the wood so the zip tie can go through the wood too. 

Use the zip tie to go though the holes in the relay and the side of the con­tain­er to anchor the relay in place with the wood sand­wiched between the relay and the side of the con­tain­er. You can see how it’s mount­ed in the pho­to below.

View of the inte­ri­or of the elec­tron­ics box. You’ll note the pow­er cord con­nec­tions do not match the instruc­tions, this is anoth­er way to do it using butt splices instead of wire nuts. The cir­cuit is exact­ly the same in both cases.

Finishing the Control Box

Now put the box togeth­er, arrang­ing the wires so that every­thing has some room in there. The wires should be loose, but if you can’t tame them, you can use some tape to hold them so they’re out of the way. Do it so that there is still enough slack in the wires so you can still open and close the box. You’ll be glad you did that lat­er. I like to put the lit­tle instruc­tion book­let for the con­troller unit in there to so that I can find it lat­er when I’ve for­got­ten how to pro­gram it.

Setting Up the Sweat Box

Now we’re going to set up the wiring in the sweat box itself.

You’ll need 4 wire nuts and the rest of the 6′ exten­sion cord for this. The cord will have more than enough length to con­nect the heat­ing ele­ments and then make it out to the con­trol box.If it seems like too much, you can cut it down.

First, you’ll need to remove the drain plug from the cool­er. On the inside, there will be a big plas­tic nut. Loosen and remove that nut: you’ll prob­a­bly need a medi­um sized pair of slip-jaw pli­ers to loosen it at first. Once the nut is off, hit the remain­ing part of the drain plug that is still pro­trud­ing into the inside of the cool­er with some­thing like a ham­mer to pop it out. It’s just held in place with a rub­ber gas­ket, there’s no glue or any­thing like that.

Now run the cut end of the exten­sion cord through the drain hole into the box so the plug end is on the out­side. Also thread the sen­sor end of the tem­per­a­ture probe into the cooler.

Use the alu­minum repair tape to tape the tem­per­a­ture probe to the inside wall of the cool­er above and to one side of the drain hole. It should be about mid­way up the side. The idea is that the heater ele­ment will be on the oth­er side so the probe is not direct­ly above the heater element.

Wiring in the Heating Elements

Connect the heat­ing ele­ments accord­ing to the dia­gram below. You will need to make a tricky lit­tle cut into the exten­sion cord about 2′ from the end: cut only one of the two wires, then tear them apart, giv­ing you two 3″ wires on one side, with the oth­er side uncut. This gives you a way to splice a heater ele­ment into the cord.

Wiring dia­gram for the inside of the sweat box

About the Heater Element Wiring

This is a side note about sup­ply­ing pow­er to the heat­ing ele­ments. In this cir­cuit, the two heat­ing ele­ments are wired in series. If you look at sim­i­lar cir­cuits, you’ll often find the heat­ing ele­ments are wired in par­al­lel. The key dif­fer­ence between the two is the volt­age that the ele­ments will get. 

If the ele­ments are wired in par­al­lel, each will get the full line volt­age. If you wire in series (you’d only do this with two iden­ti­cal ele­ments!) the volt­age will drop by half, so in this cir­cuit, each heater will get half the volt­age, or about 55 volts. 

The rea­son we’re doing this is these heat­ing ele­ments will get up to 300℉ or more at full volt­age. We don’t need that high a tem­per­a­ture, so for safe­ty, we’re run­ning the ele­ments at a low­er volt­age. At that volt­age, the ele­ments will only get to about 200℉, which is pret­ty safe as far as a con­tact burn or fire haz­ard is concerned.

The down­side is that if in the unlike­ly event one of the ele­ments blows its fuse (these ele­ments have a safe­ty fuse), the oth­er one will stop get­ting pow­er. It’s a good idea to check on the box dai­ly (you’ll be doing this any­way to cycle the beans through the dehy­dra­tor) and make sure it stays warm.

Attaching the Sweat Box Components

Once you have all the elec­tri­cal parts wired up, they need to be mount­ed so they don’t move around inside the box. In my set­up, the heat­ing ele­ments are attached to the rack I built, but you prob­a­bly won’t be doing that.

A rea­son­able and easy alter­na­tive is to use 2″ met­al “L” brack­ets of the kind found in a hard­ware store. Use zip ties to attach a pair of brack­ets to each of the heater ele­ments so that they can be attached to the side of the box as though they were sit­ting on a shelf. Use the alu­minum repair tape to tape the brack­ets to the wall of the cool­er. This is secure enough if they don’t get bumped a lot. You could use screws they give you with the brack­et if you want­ed to make them more secure.

Attaching the heater ele­ment to the side of the sweat box

Now that the heaters are both affixed into place, use strips of the alu­minum repair tape to tack the wires along the bottom/side cor­ner of the box to keep them out of the way.

On the out­side of the box, where the heater cord and tem­per­a­ture sen­sor cable come out, tape the hole up with alu­minum tape. This will keep the wires from mov­ing around and seal the box up so bugs won’t crawl in there.

Setting It Up, Turning It On

Now, you’re ready to go. The heater cord from the cool­er should be plugged into the heater plug on the con­trol box. Check the wiring again to make sure it’s cor­rect, then plu­g­in the con­trol box in.

The tem­per­a­ture con­troller will go through a test cycle and then set­tle down. There are a lot of set­tings with this device, but for the most part, you can leave it as it is with the fac­to­ry set­tings. The instruc­tions book­let is writ­ten in bro­ken English, but it can be fol­lowed. One of the set­tings you may want to change is the C/F set­ting depend­ing on the units you’re com­fort­able with.

Setting the tem­per­a­ture is pret­ty easy, just press the blue AT but­ton and one of the green num­bers will flash. Use the AT but­ton to select a dig­it, and the green up/down but­tons to set the tem­per­a­ture. For sweat­ing, we use 115℉.

Once you have the green num­ber set to your tar­get tem­per­a­ture, press the yel­low “set” but­ton to accept the change. The red “out1” light should come on, mean­ing the relay is ener­gized. There should be a red light on the relay indi­cat­ing it is allow­ing cur­rent to flow to the heaters. You should feel some warmth com­ing from the heater ele­ments if you put your hand over one.

The top red num­bers tell the cur­rent tem­per­a­ture read­ing from the probe.

These tem­per­a­ture con­troller mod­ules (com­mon­ly known as a PID con­troller) can be a bit tem­pera­men­tal, but I won’t go into too much detail here. These units are wide­ly used by hob­by­ist home brew­ers, so there is a lot of help out there if you do some inter­net search­ing using “TA4 PID” in your search terms. That’s what I do if things are not work­ing as they should.

Have fun build­ing this! If you’ve got ques­tions, use the com­ment form below.

16 thoughts on “Building a Vanilla Sweat Box

  1. This is awe­some Roland, thank you for the excel­lent detailed instruc­tions. Will start gath­er­ing the parts and hope­ful­ly have a sweat box for the next bean har­vest. I’ll let you know how it goes.

    1. Great, Anna! We look for­ward to hear­ing about it.

      1. Thank you. One alter­nate sug­ges­tion to heater. Use an incan­des­cent bulb/s of high­er wattage. Safer. In addi­tion, you can con­nect a small FAN (take from PC UPS) for cir­cu­la­tion to give uni­form temperature. 

        I had ear­li­er build a sim­i­lar set­up to test elec­tron­ic cir­cuits at ele­vat­ed temperatures.

        1. Thanks very much for your com­ments! My orig­i­nal sweat box used a light bulb as a heat source, the ceram­ic heaters are more com­pact and I think safer since the sur­face tem­per­a­ture is low­er than a light bulb and it is eas­i­er to avoid any­thing touch­ing them. The fan is a nice touch, but I have not found that to be necessary.

  2. Great tuto­r­i­al, Roland, thank you. Your oth­er tuto­ri­als on how to process the beans helped us to suc­cess­ful­ly sweat and dry our small amount of beans. They are con­di­tion­ing togeth­er now. 

    Our vanil­la vine start­ed blos­som­ing last week and we have been pol­li­nat­ing 1–3 flow­ers a day. With an expect­ed much high­er rate of suc­cess­ful pol­li­na­tion this year, your sweat box tuto­r­i­al is per­fect. Thanks again for tak­ing the time pro­vid­ing these tutorials.

    1. Just curi­ous as to what is a good suc­cess­ful pol­li­na­tion ratio?
      For me, last year was pathet­ic. This year is bet­ter (about 40%)

      1. You should be able to get to 80%, that is what we’re aver­ag­ing here. Some things we have learned:

        • Pollination does­n’t work as well in the rain when the flow­ers are wet, wait for the flow­ers to dry a lit­tle if you can
        • don’t “rub” the pollen in or squeeze it too hard, it just needs to con­tact the col­umn under the flap
        • pol­li­nate in the mid-morn­ing, just after the blooms open, but before they start to close after noon
        • use a very thin imple­ment to pol­li­nate: we use the long thorn from a thorny palm, we find a tooth­pick is too big
    2. Thanks, I’m hap­py to share what I’ve learned with oth­er vanil­la growers!

  3. Thanks for this. I was think­ing of doing a sweat box like yours before i saw your site. Never got there, just used small­er cool­ers. Another heat­ing idea is a Radiant Heat Panel, they use them for rep­tiles with ther­mostats.. I live on the west side and my orchids just start­ing flow­er­ing 2 days ago. I only have a few vines but end­ed up with 35 beans last year and 29 to fin­ish. I have all B qual­i­ty, I’m to impa­tient. Haha I cant wait to read your oth­er articles.

    1. Thanks, good tip on the radi­ant heat pan­el, I’ll take a look at that.

  4. Had a sim­i­lar expe­ri­ence where beans fell off vine with­in 2 months of pol­li­nat­ing last year. This year, I pol­li­nat­ed all flow­ers on the raceme, and only a few fell off so far (3months). I think the fail­ing, falling beans are based upon the matu­ri­ty of the vine, and the num­bers of flow­ers pol­li­nat­ed. I believe the plant can­not feed ALL of the beans if rel­a­tive­ly young. How many flow­ers on the raceme should be pollinated?

    1. This is a real­ly good ques­tion and I have to explain this to peo­ple who are help­ing with the pol­li­na­tion here. The first thing I explain is how to tell if a flower was suc­cess­ful­ly pol­li­nat­ed, which you can tell on the next day. Then we go with a rule of 5–7 beans per raceme. Once it has reached that num­ber, we stop pol­li­nat­ing it. You can tell from the size of the beans that are already form­ing how strong the raceme is, and a strong raceme can sup­port more beans. 

      A relat­ed dis­cus­sion hap­pens around the posi­tion of the flower on the raceme, which affects the shape of the fin­ished bean. Since we are not pol­li­nat­ing all of them, we try to choose to pol­li­nate a flower that is a favor­able posi­tion for bean formation.

      We’ve had a lot of expe­ri­ence with over-pol­li­nat­ing here, but I’ve nev­er seen the vine drop beans. We just end up with a lot of tiny beans. I will often break off pol­li­nat­ed flow­ers or small beans if I think the raceme is full and the beans won’t get big enough.

      So, I’m not real­ly sure about the cause of the dropped beans, we’re not real­ly see­ing that here. One thing you may want to check for is the con­di­tion of the vine itself. For exam­ple, if the feed­er roots are dam­aged, the vine may not be able to sup­port bean for­ma­tion. If you’re grow­ing in pots, it’s a good idea to make sure the feed­er roots are in the mulch where they can absorb moisture.

  5. Roland, no need to do the research on the rep­tile heat pad for ter­rar­i­ums. They do not pro­vide the amount of heat need­ed (104 degrees max), and will nev­er heat a cool­er the way your sweat box will to the required 115 degrees. I live in south Florida (Keys-zone 11). Perfect tem­per­a­ture, humid­i­ty, and rain/ dry spell to suc­cess­ful­ly grow v.planifolia.

    1. Zone 11 is per­fect. Good luck with your vanil­la grow­ing, and I appre­ci­ate your questions!

  6. I am Gerald O’Nneil from Papua New Guinea.My peo­ple plant alot of vanil­la and I am hap­py to read some of your comments.
    We don’t have buy­ers of our vanil­la and don’t know if you can help get some buy­ers for us
    Thanks
    Gerald

    1. Hi Gerald,

      Thank you for con­tact­ing us! Several months ago, I was con­tact­ed through this forum by a grow­er in Papua New Guinea. They were also look­ing for ways to sell their vanil­la, and I tried to help, but I got nowhere. I just don’t have the right con­tacts. I found one dis­trib­u­tor there Intec Vanilla Niugini Limited, they can be con­tact­ed by email at [email protected]. They look very pro­fes­sion­al, but I don’t know much about them. 

      Good Luck, I wish I had more to offer.

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