The Fresh Loaf

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Proofing Box

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davidg618's picture
davidg618

Proofing Box

The microwave oven is a fine proofing box. With the door ajar, to keep the light on, its internal temperature is 78°F. Two small, round brotforms, or two oblong ones fit snuggly, but forget baguettes, or family size challah. And if I want 89°F I'm stymied--until now.


I've been working on a proofing box since late summer, but had to put it aside for a couple of months, due more pressing things. However, I finished it last week, tested it, made one modification and really finished this morning with the door pulls. Of course it still needs a coat of stain and varnish, or tung oil, but that's just for its looks. It's functional now.


I considered insulating it, but didn't think it necessary. It's heated by a 75 watt, halogen spot light, and the heated air is circulated by a small fan--normally used for cooling electronic devices.



The light's power is controlled by a plug-in thermostat, on the side of the box, through the power plug emerging from its case. The thermostat's temperature probe penetrates the side of the box, and monitors the return air temperature. With the box empty, the circulating air maintained temperature +/- 2°.  When the box contained three pounds of dough (two loaves) +/- 2°F remained the temperature range. The lower plug powers the fan, which circulates the air regardless of the heating light's power. The fan operates at USB low voltage, so I had to provide a 120 VAC to 5 VDC power supply, the small, black box partially hidden by the light's power cord. The box's top supporting the fan and light box, is removeable, and is replaced by a smooth top; it will serve as a storage box for banneton's and brotforms when not proofing.


The box can accomodate a variety of  proofing basket shapes and numbers, a half-sheet pan, and will be used to couche proof 20" baguettes, the maximum length my oven can accept.



The one modification I had to make was build and attach a diffuser to spread the air delivered by the fan; without it the interior box maintained too large a spatial temperature gradient.



My wife is delighted. Now she can reheat her coffee in the microwave without having to first remove proofing bread, and replace it following, which she's prone to forget.


I'm delighted because I can now proof all the differing shapes I push dough into.


Davd G

Comments

matthewf01's picture
matthewf01

That's fantastic... great use of tech, which made me particularly appreciate this build. It's reminiscent of a DIY custom PC case :)

Jaydot's picture
Jaydot

How incredibly clever to be able to think up and make something like that!!
I don't suppose I can order one? :)

davidg618's picture
davidg618

I'm just too busy baking bread;-)


But, I'll be happy to answer any questions.


David G

Wingborn's picture
Wingborn

What woods and finishes did you use? 

davidg618's picture
davidg618

Wood:


one side good, 1/2" 5-ply plywood, The perforated panel, the lamp support, foil wrapped reflector base, the sliding top, and the perforated diffuser bottom are 1/4" birch plywood left over from another project. The door is a piece of finger joint aspen panel also left over from another project. Be aware, aspen is very soft wood. As you can see from my choices, looks were lowest priority.


Finish:


none yet. OK, so I procrastinate, when it comes to just looks, but it will simply be stain/sealer (MinWax), and polyurethane when I get around to it. I'm making my wife a new sewing cabinet--A1 maple 7-ply veneer core 3/4" plywood, and 3/4 hard maple for drawer fronts and covering plywood end grain. Looks were second priority on this project. I can't procrastinate finishing it, so I'll combine the proof box with the sewing cabinet when its constructed, and use the same stain/sealer and poly. I've promised it for the end of February.


Incidentally, I've stopped using water based polyurethane for indoor projects. It doesn't seem to wear as well as petroliuem based.


I'm going to  post an update about the heating system shortly (got to write it). I think you'll be interested.


David G


 

OldWoodenSpoon's picture
OldWoodenSpoon

That is an excellent solution to temperature controlled proofing on the warming side, and you are most creative!  It is very well done from a workmanship viewpoint as well.  I hope you decide to stain or oil it.  It would be a shame to cover all that nice wood with paint.


I have a number of sketches and rough drawings for a similar project, but I have been stalled on the temperature control mechanism and heat source.  I've been looking into terrarium heaters, but they all seem too low powered for the size box I want.  You have given me some ideas here that I am sure will help me move my own project forward.


Thank you for sharing, and again, well done!
OldWoodenSpoon

davidg618's picture
davidg618

...was the breakthrough for me. I've used a temperature controller making lager beer in a refrigerator (54°F) for more than a decade, but the controller's price is  $70 plus S&H, and its form doesn't lend itself to a small, neat package. I found the thermostat on Amazon for about $40, free shipping, and nicely adaptable for a countertop design. I researched heating pads, and terrarium and reptile cage heaters, but finally settled on the halogen light ($12 at Home Depot). I couldn't think of a way to avoid hot spots without using a fan regardless of what heating method I used.


Good luck with yours.


David G

Wingborn's picture
Wingborn

... is this one from McMaster Carr:


 


http://www.mcmaster.com/#electronic-equipment-cooling-fan-heaters/=aybnav


 


I like the one from Stego a lot better, but for the $100 difference in price I can deal.

Wingborn's picture
Wingborn

For a heater, look up the Stego HVL 031 series.


 


http://store.solutionsdirectonline.com/categories.aspx?Keyword=stego%20hv%20031


 


They're a bit spendy, but sometimes that is what it takes to get the job done. 


 


For a thermostat, look up the Johnson Controls A419 series.  It's twice the price of the Lux, but it's more versatile in terms of wiring and mounting.

cranbo's picture
cranbo

Your proofing box looks great! If I only had more kitchen space I would love to build something like this. I especially like the side-loading design. 


I've thought of doing something similar with:





Certainly not as nice-looking though!


 


 

davidg618's picture
davidg618

Admittedly, I went a bit overboard, although the expense was only about half again more than your estimate.  I love working with wood. This project let me combine two hobbies.


Good luck building yours.


David G

Franko's picture
Franko

It's a great looking rig David!


I'll definately be referring to your design and setup when I eventually get around to building my own. One question though, you don't make any mention of a humidity component for the proofer and I'm wondering if you included it in the proofer and forgot to mention it in the post, or if you opted not to have one at all.


Franko

ananda's picture
ananda

Hi David,


Great job, lovely woodwork and design.   As with Franko, I wondered if you need humidity.   It may well be that the box is sufficiently well sealed and insulated that you don't need it of course


Heat from light bulbs is such a confined space is remarkably effective; some friends used the same trick in one of their wall cupboards, using large plastic boxes to store the proving breads in.


Best wishes


Andy

davidg618's picture
davidg618

Franko and Andy,


I considered controlling humidity but didn't for a bunch of reasons.


I don't know what an "ideal" relative humidity is for proofing breads, and whether it is the same for all breads. I didn't have any idea how to do it in a practical (and inexpensive) way. I was concerned about water vapor condensing on the electrical components. I searched TFL for discussion threads. None were relevant, and most were complaints about highly humid weather. One post, in June 2008, specifically asked if anyone might suggest what the ideal temperature(s) and humidity(ies) is/are. There has not been a single response in 2 and 1/2 years. Searching Google revealed (as I suspected) maintaining a constant temperature and relative humidity is a complicated (and expensive) engineering challenge.


So the box is as tight as reassonably possible. I took precautions cutting and fitting the wood joints, all are glued with waterproof glue, the two penetrating holes (for electrical power) are stuffed with cotton wool, and I was especially careful fitting the doors.


Furthermore, with some exceptions, e.g. ciabatta, foccacia, challa, sweet rolls and ryes, I proof the majority of my breads in baskets, between couche folds, or panned. Ciabatta is dusted with flour, focaccia coated with olive oil, challah and sweet rolls glazed with egg wash, and rye breads cornstarch glaze. All the rest, the majority, I cover with dampened towels. I've done this for decades--long before I caught the obsessive bread-baking virus.


The point is, I think the proof box, as built, creates a stable environment, i.e., tight temperature control and an unknown but reasonably constant relative humidity.


A relevant digression: Before I retired I was a system engineer, and, often, a program manager for developing prototypes. I constantly enjoined my engineers not to "over-engineer". Engineers love to create, just because they can. I frequently laughed at myself during this project breaking my own dictum. I think I built it, yes, to "control" my bread-baking more closely, but I confess I had as much fun making the box as baking a loaf.


David G

Wingborn's picture
Wingborn

...just ask the guys over at Make Magazine. 


 


:-)

Wingborn's picture
Wingborn

...is tempered by the fact that I live in Florida.  I would only need to use the proofing box maybe 2 months out of the year.  For most of the rest of the time my problem isn't keeping things warm, but keeping them _cool_.  I have a design floating around in my head, but I'm kind of reticent about building it for this reason. 

davidg618's picture
davidg618

I bullt it because I want to ferment and proof doughs at 76°F and higher, ala Chad Robertson, all year around. Here in North Central Florida, we get about four or five months wherein our house's ambient is in the high sixtys, about a month on either end of the summer of 50's in the AM and 80's by 2 PM, and June through September we run the AC at 76, and the whole house is a proofing box.


I've got a closet too that I've converted for wine storage: 55°F year around. Perfect for retarding fermentation.


David G

Wingborn's picture
Wingborn

I'm in St. Petersburg, right at that dividing line that separates the temperate zone from the subtropical zone.  We run a bit warmer here, especially in winter.  You and I like our AC at the same temperature. 


 


I've been looking for an excuse to get a wine cooler.  Besides keeping wine, that is. 


 


So basically, I should overengineer to my heart's content, and just have fun.  I like that! 


 


Of course, if I _really_ wanted to go overboard, I suppose I could use an Arduino to control the whole thing.  :-)


 


AP

davidg618's picture
davidg618

Have fun! Wine coolers, in my humble opinion, are necessary household tools.


David G

larryparis10's picture
larryparis10

Hi David; I'm a woodworker too and have been meaning to do a proofing box as well. Yours inspires me to action. Would you please tell me the specifics on your thermostat? Thanks in advance. Larry


cranbo's picture
cranbo
davidg618's picture
davidg618

That's it.


An update: Since finishing (ok, it still needs staining and varnish) I've built levain (24hr.); proofed sourdough biscuits, and at this moment I'm bulk fermenting 1500g of 40% whole wheat sourdough. At 76°F--the house is at 67°--the box's interior warms in a few minutes, and is working like a charm. the 1/2 inch thick wood, and tight seams are enough insulation.


David G

EvaB's picture
EvaB

he built things like this, and was really annoying with his long time to get it done, because he needed the right parts etc.


What is wrong with a box, a small fan, and a regular 60watt bulb, all on the thermostat or a timer. I've seen old directions for making a proofing box, that had the bulb in the bottom of the box, with a perforated bottom and that was it, no fan, no thermostat and certainly just as neat and tidy.


I like the KISS principle myself.


Love the box, the concept and the work you put into it is fabulous, but I just think it could have been simpler.

larryparis10's picture
larryparis10

Hi David, if you don't mind, please, my reprising this thread. I now have the thermostat and I'm ready to go, except I'm confused about the diffuser. I see it on the top and the side(s) of the box, and I assume the diffuser is a box as well. Best thanks if you can forgive this noodling. Larry



davidg618's picture
davidg618

I originally cut a round hole, the sames size as the little fan, about 3" diameter, in the top of the proofing volume, and let the fan blow directly downward into the proofing volume. Using a Thermopen I roughly mapped the air's heat in the box, and found that directly under the fan was considerably hotter than elsewhere. So I simply built a small box with 1/2" holes in the bottom except directly under the fan port to spread the heated air more evenly in the proofing volume. Seems to work fine.


Here is a quick sketch of how I made it. I apologize for how amateurish it is. I made a more detailed plan, but I can't find it. Along with the posted photos you should be able to figure it out. I'll answer any question I can.



The air reenters the smaller box containing the light through a row of 1/2" holes drilled in the proofing volume's top, above the temperature sensor. I noticed that wasn't too clear in the sketch. The fan runs continuously; it's not controlled by the thermostat.

davidg618's picture
davidg618

I recently used the box at 89°F. It worked fine, but only--just like baking--after pre-warming the box. It took about twenty minutes from 70°F In the dough making I set the Desired Dough Temperature at 89°F also. The light doesn't generate a lot of heat energy. It does a fine job maintaining a desired temperature, but won't heat up a large volume of chilled dough rapidly.


David G

Wingborn's picture
Wingborn

Hey, David. 


 


To make your light bulb more efficient at heating air, do you think shining it at a heat exchanger of some sort, like aluminum foil painted black, would help? 


 


 


AP


 

davidg618's picture
davidg618

I'd have to do some research, and a little math before I'd try it.


I've been using the box a lot since I finished it (ok it still needs stain and varnish) I'm pleased with it, as is. My only caveat is I pre-heat the box, especially when I use 80°F or higher. Warming the interior wood before introducing the dough mass is important. And, I have begun adjusting the DDT to the temperature I intend to proof at when possible.


On the other hand, I used it to warm, and final proof a kg of baguette dough with good success that had been retarded at 55°F for 15 hours . I pre-warmed the box to 82°F; then I divided the chilled dough into three 340g pre-shapes, covered them, and put them in the proof box. The dough was at 72°F an hour later. I shaped them, put them in a couche, and returned them to proof box. An hour later they were ready to load. Before I had the box, I'd warm at room temperature for an hour, and proof at the same--between 68°F and 72°F depending on the weather. It took as much as 2 hours or more to final proof.


David G

larryparis10's picture
larryparis10

Hi David, and thanks. Your drawing is teriffic; I'm on my way...Larry


davidg618's picture
davidg618

I've been ranting lately about Desired Dough Temperature in another thread. It's premise is select it intentionally, and hit it as close as possible, especially if you are using a homemade proof box and temperatures significantly above room temperature.


http://www.thefreshloaf.com/node/21632/desired-dough-temperature-ddt-further-considerations


I've also made the comment here argueing, without specifics, that heat transfer into dough, using air born temperature difference only is very slow, and, because of that, one should raise the DDT to the intended fermenting temperature. A proofing box will be very good at maintaining dough temperture, but a very poor performer changing it.


Yesterday, I took a stab at making Tartine country bread. Robertson makes a big deal out of fermenting at 80°F. My room temperature yesterday ranged from 67°F to 72°F during the 3 and 1/2 hours fermenting the dough, and the subsequent 2 hours proofing the loaves (78°F prescribed). Obviously, I needed some form of proofing "microclimate" (Robertson's word, not mine.).


I've tried using my oven, but have found managing the temperature annoying. Leaving the lights on the air temperature climbs to 110°F within 20 minutes, and boiling water cools to about 8O°F in the same time, through evaporation. The microwave, with the door ajar to keep the light, gives me a constant temperture (~77°F), and the interior is too small to hold anything other than two small bannetons, thus preventlng using hot water (and forget about proofing baguettes longer than 10"). These are the primary reasons I built the proofing box.


I missed the DDT by minus two degrees, and after I'd mixed the dough in a stainless steel bowl, at room temperature, I was down to 76°F before I put it in the proofing box, bowl and all, covered with a towel I'd dampened with hot tap water. The dough weighed approximately 1.8 kg. The proofing box was set at 80°F. The dough's middle temperature after a 45 minute autolyse, and the first turn--a few minutes in the bowl at room temperature--was 76.4°F. I increased the thermostat setting to 82°F (more about this in a moment) After the second, third, and fourth turns--still in the same stainless steel bowl. the dough's temperature was 76.8, 76.8 and 75. 4 !!!. What?


I finally realized that the even though it took only a few minutes to turn the dough, with its low specific heat, the stainless steel bowl was dumping heat rapidly to the cool room. I'd taken a few minutes longer manipulating the dough for the fourth turn feeling that the dough's gluten wasn't developing quite as I'd like.


I quickly transferred the dough to the plastic container I normally ferment dough in usually beginning after the first S&F. My routine doughs are at 68-70% hydration and I find leaving them in the bowl and doing a bowl turn before beginning bench S&F's is less messy. Robertson prescribes bowl turns throughout the fermentation process so I'd figured "Why dirty another container?".


At the end of the 5th turn the doughs temperature was 77.8°F. I still wasn't happy with the gluten development, so I did one bench S&F, felt the resistance I'd wanted, and returned to dough to the proof box. I didn't bother taking the dough's temperature. I shaped the loaves, put them, covered (dry towel) into the proof box still set at 82°F. I chose not to take their temperature preferring not to poke holes, even in the bottom of the loaves


One last comment: I've said before heat transfer into bread dough is a complicated process involving the dough's initial temperature, surface area to volume ratio, and its a physical property known as specific heat. In a proofing box relying entirely on warmed air to carry the heat energy, the air's temperature vs. the dough's temperature is, of course, also a factor. The optimum range for yeast (commercial) development is 68°F to 81°F, with maximum production at 79°F (link 1). Similar curves(Link 2) show similar performance for yeast associated San Francisco sourdoughs.


Link1: http://home.earthlink.net/~ggda/yeast_treatise_frameset.htm


Link2: http://aem.asm.org/cgi/reprint/64/7/2616


I use 90°F as a safe upper limit to ferment dough, and therefore the highest setting I'll heat the air in my proofing box to. Even though the center of a dough mass will remain cooler, the air's temperature will ultimately penetrate an undisturbed dough deeper and deeper toward its center, with yeast growth diminishing in more and more of the fermenting dough. Periodic manipulation, e.g. turns and S&F evens out the dough's temperature distribution, so all temperatures above 82°F will ultimately slow down yeast growth. The consequence is there is only a small differential between usual room temperature and 82°F in which to operate.


Obviously, the way to warm dough quickly, i.e., transfer heat energy into the dough most rapidly, is use a large heat source, at a non-damaging temperature, and manipulate the dough rapidly and continuously. But, of course, we already do that; we call it mixing which puts us right back to the importance of DDT.


David G