The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Large Proofing Box from a Broken Fridge or Freezer?

chris d's picture
chris d

Large Proofing Box from a Broken Fridge or Freezer?

Looked around a little here (but not a lot) and was wondering if anyone had any experience with making a proofing box out of an old refrigerator, working or broken. It seems an obvious solution to creating a large temperature-controlled environment. Much of the same stuff used to make smaller proofing boxes could be adapted to this solution. 

A working refrigerator could be outfitted with the sort of on/off thermostat that people use for brewing, and perhaps some sort of humidity control could be added?

Thanks in advance for any leads on other who have done this.



drogon's picture

The fridge has insulation to start with - which works both ways - keeps heat in or out!

There was a thread here recently about making a proofing box too - the simplest is going to be a 40 watt bulb and a thermostat.

I'm in the (slow) process of getting all the bits together to make a combined retarder/proofer using solid state coolers/heater (peltier devices) and those water misters to create humidity - combined with a raspberry Pi to control it all, (and my ovens) but I'm a geek, so that's relatively easy for me... I'll post when done - but not expecting before March!


chris d's picture
chris d

I like that idea and would be excited to see what you come up with. Kind of killing a gnat with a sledgehammer, but I totally understand your enthusiasm. :)

I have a Raspberry Pi at home that I'm running an apache web server and some open source software (OptiRain) that's wirelessly controlling a really neat sprinkler controller (the EtherRain). I suppose I could use the same Pi to control some arduino bits wirelessly as well. Hmm... Just what I need...another project! Ha!

I was thinking about peltier effect modules for the thermal control. You wouldn't happen to have a good link to share for some DIY direction on using them and where hobbyists procure them would you?

Let me know if you post up some progress reports!

sandydog's picture

Hi Chris,

I just recently put "Proofing Box" into the search function - There were lots of pages with just the sort of helpful information you will enjoy.

On page 2, I found a (Long forgotten) post from myself which drew lots of help from our members - You could start your research there if you wished - It doesn't really matter what your box is made of, it could be a cardboard box, an old microwave or indeed in your case a refrigerator. If your fridge is operational then obviously you could use it for both retardation and proofing.

I finished up using a large cardboard box and a reptile heat mat linked to a thermostat - It works just fine.

Good luck with your project, and happy baking.


chris d's picture
chris d

I'll have me a look. I did a similar search and without reading everything it returned, I saw there were a lot of discussions about proofing boxes in general. When I start digging into specifics, I'll begin with your post.

barryvabeach's picture

Chris,  I have used a wine refrigerator as a proofing box, unplug the fridge, and put in a heating pad hooked up to a temperature controller, it works pretty well. The main benefit you will have with a fridge is that with such good insulation, you won't need a lot of heat.  Can't help on the humidity.  I sometimes put in a small dish of water with a sponge mostly in the water, but part out of the water.  My guess is that will help humidity, but never measured it.

chris d's picture
chris d

Are you talking about a seedling heating pad? any chance you have a link to the particular one you use?

saintdoughco's picture

Hi Chris,

I know this post is quite old! I've been searching the site on DIY Proofers, and just saw yours about the heating pad and empty wine cooler, do you have a picture at all of your setup if you still use it or used to use it?


Mini Oven's picture
Mini Oven

ventilation or your fridge might be a great place to grow mold.  leaving the door open when not in use, etc. 

Essam Haroon's picture
Essam Haroon

That is a great advice.

barryvabeach's picture

Chris,  I use a regular heating pad from a drug store, together with a PID like this one   I don't recall which seller I bought from, there are many that sell that unit.  I wired the controller to an electrical outlet, so I just plug the heating pad into the outlet, and set the temp.  I just did a search and see they now sell similar models in F, which would be more convenient. You could use a lightbulb as a heating source as well, my point is, your fridge is pretty well insulated, so you won't need a tremendous amount of heat to keep it at temp once it is close to the right temp.

davidg618's picture

I built this proof box 4 years ago, and still use it with pleasure.

I have a small house, and a lot of hobbies--they all take up space, some more than others. Needless to say, yet another refrigerator (I own 2 now), or another wine cooler (I own two now, and also converted a closet into a 160-bottle wine storage) was out of the question.

However, had I the room I would have likely used a third refrigerator, for the very reason Chris, et al, reason. I could warm or retard in the same "box".

I live in north-central Florida, but I'm guessing my experience is probably nation-wide: 2nd hand refrigerators are cheap. I've bought two full-size refrigerators via online, local "for sale" websites. $100 for  the first (it broke after 4 years use) $125 for the second. I've also bought two 30 bottle wine coolers each for $100. I use one as service storage, the second one I use as a fermentor: lager beers ferment best in the 45°F to 55°F range, and fermenting white wines and meads preserve their fruitiness and flavors better than at room temperature when cooled to the 60's. I'm also considering adding a humidifier and temperature/humidity control to the second one for making/aging cheeses and dry-cured sausages, etc. That will cost an additional $150, so I haven't committed yet.

I also own an external temperature controller I bought 20 years ago for about $50 that controls a working refrigerator to +/-2 degrees by simply monitoring the internal temperature, and turning the external electric power to the reefer on or off. In today's market similar controllers are $80. There are digital temperature controllers available for a lot less, but I haven't researched their specs yet, so I can't comment on them.

As to Mini's valuable caution, cleanliness (and cracking the door when not in use) will suffice. I've kept my RV's often in-active refrigerator pristine for 12 years that way.

Bottom line: for a few bucks more, and the room to house it you can make a multi-use heater/cooler with much more than a two-loaf room limit for less than $200.

(When I win the lottery I'm adding ROOM to the house, and all the right toys for all my hobbies.)

Happy baking,

David G



BobBoule's picture

You've motivated me to consider this approach. In my case I'm thinking that I will get a small mini-fridge, a heating pad and one of those appliance timers that has two outlets on it. Placing the heating pad on the bottom and set to 100 degrees, I'll plug that into the first outlet on the timer and set it for my proofing time then plug the fridge's cord to the second outlet and set that to start when the proof time has elapsed. That way its fully automated and can be retarded for several days without any attention from me. Thanks!

davidg618's picture

I'm not sure I fully understand what your planning, but there's a few things that caught my attention, and may not support what you are trying to achieve.

I'm not familiar with appliance timers, but I think you're saying you will heat the interior of a small refrigerator to 100°F for a given amount of time proofing bread dough, and subsequently return it to typical refrigerator temperatures (38°F - 40°F) and retard the dough for an unspecified number of days. You haven't been specific re what you are going to proof (bulk dough or shapes) and retard.

First let's look at temperature.

Take a look at the graph I posted in 2011. It plots the normalized growth rate of two similar lactic acid producing bacteria (red and green) and an a symbiotically associated natural yeast (blue) in a sourdough culture, vs. temperature.

You can readily see the temperature for maximum growth (the sweet spot) of the yeast is 82.4°F, and at 100°F yeast growth falls to zero. Conversely, bacterial activity, for both strains, peaks approximately at 100°F. Consequently, if you are using sourdough levain in your dough, and your goal is to maximize sourness in your dough mix 100°F is fine, but if you're goal is to maximize yeast activity you've chosen the wrong temperature.

Similar curves available on commercial yeast manufactures websites will reveal 82.4°F is the sweet spot for commercial yeast strains also. In fact, Zojirushi bread-making machines "preheat" and "rise" cycles are warmed to 82.4°F to maximize dough expansion in minimum time.

Also, bread dough enzymes aren't all beneficial to the bread making process all of the time. Wheat flours contain protease enzymes that weaken the gluten network. In the short term that's a good thing. Doughs baked within a few hours of mixing will enjoy soft, chewable crumb. At some point, however, the protease present will chop up the gluten network into a runny mess, and your baked bread will be, literally, "flat as a pancake".

I don't know a general rule of when this becomes a problem in retarded doughs. I only know 15 to 21 hours for lean wheat doughs is OK. These are the minimum and maximum times I retard doughs I bake. I've read of baker reporting retarding dough two or three days who still claim success in the finished loaves. However, there is a limit to how long you can retard doughs. I witness this phenomena, every week, in my refrigerated sourdough seed starter. After five days the once strong gluten network is weakened to the point that it can't support itself. After ten days its entirely runny.

I think your technical idea is sound--heating pad, timer, and small refrigerator. However, I also think you need to study yeast and dough behavior over time and temperature excursions.

If you want more detail about bread dough enzymes check out this site.

Happy Baking,

David G



suave's picture

The problem is, even if you dough is warm, and your kitchen is 70F, then after preshaping, resting, and final shaping it will cool down significantly.  Setting proofing temperature somewhat higher than optimal allows the dough reach the desired temperature faster.

BobBoule's picture

that makes a lot of sense, thank you!

BobBoule's picture

David, thank you. I did search online before joining TFL a year ago and found several charts like this one, unfortunately none of them disagreed so I picked the one that seemed the most authoritative and went with that. I have been using 100 to 110 degrees F for proofing (bulk dough) then just shoving it directly into my fridge for three days. With the mini fridge I'm just trying to automate his part of the process so I can bake more often (I'm a consultant with an erratic/unreliable schedule). Its worked very well for me. As part of this experimentation, I've even done my bulk proof at 120 degrees F (after checking my thermometer's calibration) and it works just fine, and baked a fine loaf of bread.

The chart I have been following indicates that the die off occurs at 130 degrees F but the curve is shaped identically. It amuses me that there could be a 30 degree difference between the two charts and will continue to look for more information to explain this discrepancy, when I have time. Thanks for reminding me about this controversy and thanks for the article on enzymes, I'm really enjoying it.

Just to make it a bit more complex, I do follow the Rule of 240 for setting my water temp just before mixing it but then I proof at the higher temperature.

It looks like I'll have to run some experiments to see what bulk proof temp works best for me and then se which chart it fits then work my way back to the source of the chart and see what other info I can glean from them. Thanks again.

davidg618's picture

Your approach seems to be outside the box of common baker practices, but if it works for you, and you're happy with the results--great!

Would you please send me links to the graphic references you mentioned?


David G


BobBoule's picture

that I originally found them on, so far I only found a few of them, but I'll post more if I can find them.

I did notice that the beer brewing sites seem to indicate that different strains of the yeast that they use will maximally ferment at a different optimum temperature for each strain. I wonder if I will experience those differences, or is all Baker's Yeast exactly the same?

davidg618's picture
davidg618 rethink what I thought I understood about oven spring. Your third reference was the catalyst. I bookmarked it some years ago, but haven't looked at it for a couple of years. I may post something when my head is clear.

Beer yeasts fall into two broad categories: top-fermenting yeasts and bottom-fermenting yeasts. Ales are fermented with top-fermenting yeasts at room temperatures. Lagers are fermented with with bottom-fermenting yeast in a cooler range (mid-40's °F to low 60's °F). Bread yeasts are more akin to top-fermenting yeast. Historically, before Pasteur isolated yeast and revealed its major role in fermentation in the late 1800's, bakers often obtained "barm" from the head on fermenting vats of ale at the local brewery.

In the context of bakers yeast in lean doughs I think all brands perform about the same way, One can also find osmo-tolerant yeast for doughs containing a lot of sugar. Wikipedia has a good summary article about bakers yeast.

David G


Kitchen Barbarian's picture
Kitchen Barbarian

AGPtek Digital All-purpose Temperature Controller STC-1000 w/Sensor

Comes with the sensor probe.  There is also

Elitech 110V All-Purpose Temperature Controller+ Sensor 2 Relay Output Thermostat Stc-1000

This is a few bucks cheaper and says in the title that it has the sensor probe with it - but the probe is not listed in package contents, only the control unit itself is listed there.  Many of the questions posted and some of the reviews seem to imply it includes the probe; but should you get one without the probe, since it is not listed in package contents, you would have limited recourse.

Make sure its the 110V version. That unit is rated for up to 10A.

I have seen it said that there is a version that will display in F instead of C, but I've never been able to find it.

Instructions here, you don't need the extra relay they discuss at the bottom of the article unless you are trying to control the compressor motor (ie you're plugging the fridge into this).  For just lights or some other heating device below 10A, it isn't needed.

The unit will control for heating or cooling, but only for one at a time - you can't use the same unit to control both phases.

This device would give me:

  1. 80F - proof bread
  2. 90F - incubate dosa/idli batter
  3. 104F-109F - incubate yogurt

Pretty multipurpose, eh?

There's also this:

Commercial Food Pastry Warming Case

If it works as advertised ...  It says it can be set from 0 to 200F, but clearly there's no compressor in it, so it is only going to heat and that only if you set it to a temp above ambient. As long as I can go from 80F up that'd be good.  At 185F, I could slow-bake cheesecake in it!!!!

I have no idea how stable or accurate the temp is in that however.

doughooker's picture

There was a guy who promoted units he built around these controllers a few years ago on TFL. I had him build me two of them and I just love them, can't bake without them. He lives in China now. He builds the controller into a plastic case and attaches two AC cables, one with a male plug and one with a female socket. They're plug and play -- no assembly required. I use one to control a heat lamp which keeps my sourdough starter and dough at exactly 30 C. Converting Fahrenheit to Celsius is trivial.

I'm sure a probe comes with it. They may not list it separately because it is attached to the unit. If it doesn't have a probe, which seems highly unlikely as it would be pretty useless without some kind of sensor, you could return it to Amazon, so you do have recourse.

There is also this. It looks like it has AC cables attached.

Kitchen Barbarian's picture
Kitchen Barbarian

I don't think he's making them any more, at least he's not selling them through the link he left here.  I remember talking to him about the controller.  But when I finally got up the energy (more like the money) to buy one - POOF!  No longer available!

As I recall they were only around $50 or so - not bad for avoiding doing the dirty work yourself.

SaccharomycesCerevisiae's picture

Hey! So I actually had the exact same idea.   I was looking around at other homemade proofers, and was initially going to build my own box from wood.  Then I thought, hey I can buy a cabinet or something that's already made with doors, and change it for my needs.  Then as I'm strolling around Home Depot looking for ideas, I see a little wine cooler/fridge.  Voila! Perfect!  So I bought a wine cooler off Craigslist, got a spotlight (heat), pocket thermometer and hygrometer, shelves, and programmable outlet thermostat.  I just used a wet towel on the bottom for moisture.  Maybe the whole project cost me $150.  But it's perfect!  I'm curious if you have made yours yet and what you did.  I only just finished mine, and made my first 4 loaves of bread today.  Heat around 80-84 F and humidity between 35-50%.  Worked great! My thermostat isn't in this picture (I had taken it out to finish programming it), but you get the idea.

rgconner's picture

Funny, I want to do this too.... but to make cured meats =)

doughooker's picture

I do my proofing right in the mixer bowl! I have a thermostat and a red heat lamp shining into the bowl -- keeps the dough right at 32 C. There is a sheet of cling wrap over the top of the bowl. You don't have to move the dough around as much, and I love the eerie red glow of the heat lamp.

gerhard's picture

I use two light bulbs controlled by a dimmer switch inside a reach in commercial fridge, not high tech but it has worked for the last 20 years.  I use it for all kinds of things including melting pails of coconut oil, melting peanut butter and white compound coating it is very versatile.


barryvabeach's picture

Saintdough,  I saw your post about asking Chris about the wine cooler proofer.  This is mine, and yes I still use it ,  either for warming or cooling , depending on what I need.  At the bottom center of the photo, you see the little digital controller I used for the heating pad.  On the left lower side of the cooler, it is hard to make out, but there is a short black thin gauge extension cord that goes into the cooler that the heating pad plugs into, it is thin enough that the door closes, but it designed for household current.  On the right side of the wine cooler, you can see some blue tape, that is for the sensor to the digital controller.  The electric strip and the timer in  it at the bottom of the photo are so that I can set the proofer to run at a cool temp for a certain number of hours, then go to warm  ( though when doing that there are actually two timers plugged into the strip).   Currently, the cooler is plugged into the extension strip, just because it has an on off switch that is convenient. 

In terms of heating source,  I find the heating pad works great, but you have to either get one that does not auto shut off after 20 minutes, or if you do get one of those, you have to hack it so that the auto shut off feature is disabled.  I also put a foam board above the heating pad, to make the heat a little less direct, and for ease of sliding things in and out  I think this is the site I used to hack the warming pad