Curing Chamber Development

[Chris Hennes]

For the past several years I've used a wine fridge as a curing chamber. This had the advantage of being dead simple: I just set the temperature as low as it would go (55°F, 13°C) and left it alone. This worked fine for short cures (a month or so), but the temperature control was poor, and humidity was controlled via the wet salt method, which results in humidity that is a bit too high. Because the cooling was thermoelectric, during the hot summer months here the fridge ran constantly and was still more like 65°F/18°C, which is bit higher than I would like. I also wanted to move the chamber to the garage so it wasn't taking up space in the kitchen, which would be completely untenable in the summer with only thermoelectric cooling. They also proved to be unreliable, repeatedly breaking down over the years (I've replaced both fans and Peltier units in two fridges). 

 

SO.... I wanted a new, more reliable, more accurate, more controllable system. I also wanted an excuse to goof around with my fledgling microcontroller skills. Here are the goals of the project:

1. Temperature controlled to any set point between 10°C and 38°C (for fermentation stage).
2. Humidity controlled to any set point between 60%RH and 90%RH.
3. External readout of temp and humidity.
4. Long-term average display of temp and humidity.
5. Looks cool.
6. Is fun to create.

Actually, number six was probably the primary driver here, if I'm being honest with myself. The others followed from that!

 

To address temperature control over that range, I needed to use a compressor-driven refrigerator, rather than a thermoelectric unit (basically none of which can reliably get the interior temperature that low when living in the garage). At the other end of the spectrum the plan is to simply use a lamp as a "heater" -- this is unimplemented as of yet, because I don't need a fermentation stage in my current curing projects. For humidity control the plan was to use a humidifier in a box below the fridge that vents into the fridge itself, and to use an exhaust fan at the top of the unit to dehumidify (given the nearly-always-low humidity here in central Oklahoma). I have not implemented the actual humidifier yet because I don't need upward control at the moment, my problem is dehumidification.

 

To control all of this I am using an Arduino Uno development board coupled with a DHT22 temp/humidity sensor, plus four pins used to control the fridge (via an AC relay), lamp (AC relay), humidifier (AC relay), and exhaust fan (transistor). I've also got a 16x2 LCD wired up to display the status and averages.

 

Here is a shot of the breadboarded system (obviously once I'm happy with it I'll ditch the breadboard...):

 

The LCD is set up to display the current conditions on the top line, and a rotating set of averages (hourly, daily, and monthly) on the bottom line:

 

Here's the installed prototype (you can see the chamber for the humidifier below the fridge):

 

A closeup of the electronics:

 

The sensor placement (obviously not permanent, the whole thing is still in the prototype stage):

 

My fancy dehumidifier (there is a hole drilled into the fridge beneath the fan):

 

If you are of a technical bent you can see the control code at GitHub. Once I've finalized the system I'll also publish the schematics there.

 

[gfweb]

Neat!

 

What is the airflow pattern?

[Chris Hennes]

The inlet's at the bottom, and is 4.5" across, outlet's at the top (1.125"). These are the fans I'm using. No idea the CFM.

[Martin Fisher]

That's very cool....I have 2 chest freezers currently set-up as curing chambers (no inlets or outlets...I use fan-driven desiccant to remove moisture.)

I've wondered about the fridges like you have without the "freezer"....can stuff get behind the coils (rogue mold or whatever) where it can't be cleaned?

[Chris Hennes]

I'm not terribly worried about "rogue mold" hiding in the crevasses of the fridge. First, because there isn't going to be much in the way of food for it there, and second, it's not like my garage is a cleanroom environment! There are myriad spores floating in the air and being blown through the chamber. If you get the temperature, humidity, salinity, and pH right, you should be OK.

[Martin Fisher]

Well, my intent is to use the small fridge as a cheese cave (for blue cheese), which is a bit different than a curing chamber.

So, there isn't an easy way to clean behind that plate?

[Chris Hennes]

Not that I can see. I suppose you could consider putting some type of thin plastic shield over the entire back section that could be removed for cleaning if you were really worried about it. Don't you inoculate blue cheese? It seems like the desired mold would out-compete any random bugs coming in from elsewhere, sort of like sourdough.

[Martin Fisher]

Yeah, seeding the cave with Penicillium Roqueforti is proper procedure.....but encroachment by other stuff isn't an impossibility.

I was just looking for a small compressor driven fridge that's easy to clean and disinfect, if need be.

[gfweb]

The inlet's at the bottom, and is 4.5" across, outlet's at the top (1.125"). These are the fans I'm using. No idea the CFM.

Isn't hard to keep a steady humidity and temp with outside air coming in?

[Chris Hennes]

The point of the outside air is to lower the humidity: when the humidity is in the correct range the fan doesn't run. And the fridge controller handles the temp. Of course everything is coupled, but the controllers have so far managed to work fine.

[Chris Hennes]

Here's a plot of the first day's temperature and humidity. Note that it was cold that day, so the compressor actually never had to turn on, only the humidity was being actively controlled. The target temp was 15°C ±3°C and RH was 65% ±5%.

[Simon Lewinson]

Well, my intent is to use the small fridge as a cheese cave (for blue cheese), which is a bit different than a curing chamber.

So, there isn't an easy way to clean behind that plate?

Pretty easy to do in my opinion. I would use a strong chlorine bleach solution, spray liberally around all areas and then close it up with a fan running to circulate the chlorine fumes for a while. Dry out quickly with a hot air gun and then keep it closed. Don't think that much in the way of mold would survive this.

Simon

[dcarch]

That is basically my setup, a 4.5 cu. ft. refrigerator converted.

 

Except mine is also an indoor smoker, using an external cold smoke generator. Heat for smoking is actually a 500 watt halogen bulb dimmed to 300 watts. It can get temperature to 200F for smoking. Any higher may melt the plastic interior.

 

Moisture is added using an ultrasonic humidifier.

 

dcarch

[Chris Hennes]

Do you have issues with residual smoke flavor affecting unsmoked products?

[Tri2Cook]

Just out of curiosity, because I've been bouncing the idea of a curing chamber around in my head for a while now, is what you're doing a better setup than something like this (which is what I was planning to use) or is it more for the satisfaction of the DIY? I think it's really cool that you're working out the setup you want/need yourself but I'm probably not as inclined to make the effort if something like what I linked to will work.

[Chris Hennes]

It depends on your needs. I can actively control humidity and temperature both up AND down with my controller: the module you linked to can only control up OR down (it will only control two devices, not four). It is also substantially more expensive than my solution. Of course, the truth of the matter is that I chose my route because I wanted to play around with the DIY aspects.

[Tri2Cook]

That makes sense. With the one I linked to, controlling temp up and down should be fine but I'd have to choose with the humidity. Which kinda makes it not all that efficient unless the environment where the chamber is located is pretty constant. I'm leaning towards putting it in my basement which is pretty humid during the warm months and pretty dry during the cold months with the temp being fairly stable... so the controller would actually be almost opposite of what I'll probably need.

[Martin Fisher]

Auber does sell a dual-output humidity controller. 

[KennethT]

I know you said you're using the fridge's controller to control temp, but if you're turning the fridge on and off - really, you're controlling it that way... I haven't had a chance to check your code, but I would just make sure that the fridge can't turn on/off that frequently as it will greatly shorten compressor life.

[Chris Hennes]

I'm not using the fridge's controller at all, it's set to as high as the fridge will go but that is still considerably too cold. The PowerSwitch Tail, controlled by the Arduino, cycles the power to the fridge. The code's got a timer in it that prevents the fridge from cycling too rapidly, and in practice the set temp is so high by normal refrigeration standards that the compressor is switched on far less frequently than it was designed for.

[dcarch]

The use of Peltier device can be interesting in that by reversing polarity, it can also provide heating.

 

dcarch

[dcarch]

Do you have issues with residual smoke flavor affecting unsmoked products?

 

Not so much. The cold smoke generator is motorized to give very thin smoke (TBS) for smoking, and the smoker's door is open most of the time to vent residual smoke flavor.

 

dcarch

[Dave W]

This is a very cool build Chris it makes my converted wine fridge look kludgy.

Do you see a lot of benefit from having the humidifier external to the chamber? I have my ultrasonic humidifier in the chamber and I get concerned about mildew, or eventual damage to the electronics.

[Chris Hennes]

I did it to save space in the fridge, but I won't really know its effectiveness until it needs to run. Right now dehumidification is the issue.

[Dave W]

Yeah living in CO dehumidification is really never an issue for me. So far anyway. That humidifier does take up a good couple cubic feet in my chamber though and it's locally way more humid right next to it.

 

I agree with you regarding rogue mold hiding in your fridge. Innoculate with healthy mold for a few generations, control your environment, never sweat it again.

 

Dcarch I think that's pretty cool that you've got a cold smoker set up inside somewhere. I'm fairly sure my wife would actually kill me if I did that.

Edited November 25, 2014 by Dave W (log)