controlling humidity in curing chamber

[Mmmm Meat]

After making a mess of my first attempt at bacon, I learned that asking questions earlier rather than later saves a lot of frustration. I got great help with that issue so I'm pushing forward into a new project - a charcuterie meat curing chamber. I've though about doing this project for over 20 years, since the time I was stationed in Sicily while in the Navy. I had several opportunities back then to sample homemade Italian salumi that were incredibly good. Concerns over the botulism poisoning kept me from attempting my own curing setup years ago. The advent of YouTube instructional videos over the past few years has led me back to that original desire to cure meat at home after seeing that it really is a manageable project that can be done safely.

So anyways, I had a 3.2 sq ft. minifridge sitting unused in my garage. I'm posing pics of the cooling plate that apparently has refrigerant running through it to cool both the small freezer space above it and the main chamber of the fridge below. I ordered Inkbird temp and humidity controllers, a small ultrasonic humidifier and a small dehumidifier similar to models I've seen recommended on various sites and installed them in the door shelves (in order to maximize the remaining curing space in the main 'fridge chamber). I added a 12V DC fan with a variable rheostat that is still too powerful for this small setup, though for testing the controllers, it is fine as is and seems to help equilibrate humidity levels faster while I'm playing with RH settings. Also, I have not yet sealed the hole cut into the side of the fridge for chord placement. Though I placed some tape over most of the 1.25" opening, the chamber still seems to be affected by external RH.

Similar to many other people using mini-fridges for curing chambers, the temperature seems easy to maintain but the humidity values swing wildly when either the humidifier or dehumidifier is used. I've not tried them working together at the same time since I'm sure they would both run in an endless battle to add or remove humidity.

I live in SW WA. We experience wide swings of relative humidity depending on if the weather either feeding in off the coast or instead, coming from the dryer interior regions. I've seen the RH range from 45% to 98% in the last 12 hours of monitoring outdoor and indoor humidity. I've been playing with adjustments on the Inkbird controller and found that once the humidifier turns off, the RH will still rise around another 10% above the target. If the exterior RH is above 80%, then the internal RH continues to click slowly higher and can reach above 90% with time.

When I run the dehumidifier, it works slowly but effectively when the external RH is above the target point. When external humidity is below 60%, the dehumidifier can easily remove an additional 20% humidity in just a minute or two after the controller turns it off. I believe that is because it utilizes thermoelectric (peltier) cooling, which I imagine continues to dehumidify until internal temperature equalizes across the heat pump gradient (at least that's my best guess). The chamber often gets down to 52% or so if the dehumidifier is run for more than three minutes or so, even though the controller turned it off at 71%. Additionally, it seems that since both dehumidifier and humidifier always have at least some water in their tanks, that internal pool of water is also causing some increase in RH even when those units are off.

Anyways, there's a lot of moving parts to this initial setup and I'm feeling a bit frustrated with my inability to manage the humidity better. I'm hoping that some of you have ideas that might ease my suffering and at least reduce the radical humidity swings I'm experiencing. Thanks in advance for your help.
George

 

[indaswamp]

that is a long post, but I will attempt to address some of your concerns...

Concerns over the botulism poisoning kept me from attempting my own curing setup years ago.

Education, education, education. That is the answer for your fears. If you have not yet bought to book The Art of Making FERMENTED SAUSAGES by Adam and Stanley Marianski, then order it today. Best $20 bucks you will spend for your education.

I've been playing with adjustments on the Inkbird controller and found that once the humidifier turns off, the RH will still rise around another 10% above the target. If the exterior RH is above 80%, then the internal RH continues to click slowly higher and can reach above 90% with time.

As you have found out, adding humidity is easier than removing it. High humidity will be your biggest problem using a non-frost free unit as a curing chamber. Small spaces have wider swings. Moisture is condensing on the coil plate when the unit runs, and when it shuts off, that water (not the water in the humidifier and dehumidifier tanks) evaporates which gives the humidity spike. Using one controller to target the same set point for both humidity and dehumidify is a recipe for dueling units. It is better to use two different controllers with different set points and target a range. Set the humidify set point lower to accommodate the overshoot in RH%.

 

[Mmmm Meat]

that is a long post, but I will attempt to address some of your concerns...

Education, education, education. That is the answer for your fears. If you have not yet bought to book The Art of Making FERMENTED SAUSAGES by Adam and Stanley Marianski, then order it today. Best $20 bucks you will spend for your education.



As you have found out, adding humidity is easier than removing it. High humidity will be your biggest problem using a non-frost free unit as a curing chamber. Small spaces have wider swings. Moisture is condensing on the coil plate when the unit runs, and when it shuts off, that water (not the water in the humidifier and dehumidifier tanks) evaporates which gives the humidity spike. Using one controller to target the same set point for both humidity and dehumidify is a recipe for dueling units. It is better to use two different controllers with different set points and target a range. Set the humidify set point lower to accommodate the overshoot in RH%.

Thank you for the book selection. I'll get that one for sure. I think that I may have seen your recommendation for two controllers for humidity elsewhere on a different thread. I was considering this option, though I thought I'd ask before buying. The wife is already questioning my purchases to date. I'll have to hide this one from her.

I saw a different suggestion regarding use of a bowl of sodium chloride/water solution to maintain humidity at 75%. Is this a functional idea that would work when meat is in the chamber too?

Thanks!

 

[indaswamp]

I saw a different suggestion regarding use of a bowl of sodium chloride/water solution to maintain humidity at 75%. Is this a functional idea that would work when meat is in the chamber too?

I don't recommend it. It may work for a few days...maybe a week...but it takes vigilance and attention to regular checking and refilling. the evidry is the best option out there IMO...unless you live in Italy....or San Fransisco....

 

[indaswamp]

I'm hoping that some of you have ideas that might ease my suffering and at least reduce the radical humidity swings I'm experiencing.

Get a larger, frost free chamber. Look on craigs list or facebook market place and buy a used frost free refrigerator. They can be had for $100 or less in most places...just make damn sure it is frost free!

 

[indaswamp]

With your current set up, you will not likely need to ADD humidity once product is in your chamber...at least not for the first month or so of drying. And if you keep it full, maybe never....the new product will supply all the humidity you will need.

 

[indaswamp]

I think that I may have seen your recommendation for two controllers for humidity elsewhere on a different thread. I was considering this option, though I thought I'd ask before buying.

It's another $35 bucks for the inkbird humidity controller...well worth it IMO after running separate controllers for humidify and dehumidify in my new set up. Very smooth with no dueling controllers.

 

[BGKYSmoker]

Dont use that dinky fridge unless you have a way to plug the lines and remove that ice compartment.

 

[Mmmm Meat]

It's another $35 bucks for the inkbird humidity controller...well worth it IMO after running separate controllers for humidify and dehumidify in my new set up. Very smooth with no dueling controllers.

I placed the order. Just curious what numbers you set your two humidity controllers at. Can you give me a hint just to give me a reasonable starting point?? Thank you again for your help!

 

[Mmmm Meat]

Dont use that dinky fridge unless you have a way to plug the lines and remove that ice compartment.

I understand the small one is not optimal in functionality, but I and my two young kids are the only consumers of cured meat in the house. I expect that even small batches in a small fridge will produce more product than the three of us can consume. I'm thinking though that some mid-sized unit might make life a lot easier. Maybe a beverage cooler? I may pursue that if I can produce some quality cured meats with this small one. Baby steps....

 

[indaswamp]

I placed the order. Just curious what numbers you set your two humidity controllers at. Can you give me a hint just to give me a reasonable starting point?? Thank you again for your help!

Your parameters will be different than mine...I have a frost free unit which draws down the moisture in the air during the cooling cycle as humidity condenses on the evap. coil then drips down the drain.

I currently am not running my humidifier at all, rather I am allowing the RH% to be pulled down to around 71%, then when the cooling cycle is complete, the RH% rebounds quickly back into range. Dehumidifier is set to turn on @83.5%RH.

It is worth mentioning that the RH% will usually be 5-7% higher if you hang the probe down with the salami (within 1-1.5" of the side of the hanging salami) than if you put it on the shelf 5-7" above the salami where they are hanging....at least in a chamber 14cu. ft.... might be different in your small chamber.

 

[indaswamp]

Maybe a beverage cooler?

Rick is your man if you buy a beverage cooler for a chamber....he use to have an old Sobe drink cooler for a chamber......

 

[BGKYSmoker]

I understand the small one is not optimal in functionality, but I and my two young kids are the only consumers of cured meat in the house. I expect that even small batches in a small fridge will produce more product than the three of us can consume. I'm thinking though that some mid-sized unit might make life a lot easier. Maybe a beverage cooler? I may pursue that if I can produce some quality cured meats with this small one. Baby steps....

If you can get a small single door fridge wit out the freezer shelf that will work. Think lowes i got mine for like 179, make sure it uses a compressor for cooling and try to keep your items away from the back of the fridge as thats where the cooling lines are, the back can freeze quick. Target in the pharmacy has a very small cool mist humidifier that works well in smaller cabinets.

 

[verbage]

In my own experience using a small refrigerator (3.2 cubic feet like yours) and a slightly larger beverage cooler (4.4 cubic feet), the issue has never been the need to remove humidity, but the need to supplement it to prevent case hardening. Because these small devices hold a very limited volume of air, as soon as the compressor kicks on to cool down the unit, the humidity is instantly drawn to the coils, which dries out the ambient air to such a degree that it promotes case hardening. I attach a temperature/humidity plot from the 4.4 cubic feed beverage cooler during a drying run so you can see just how tightly the two are coupled.

The stage of your drying process also makes a huge difference--earlier on in the drying process, when your products still have lots of moisture, less added humidity (by the ultrasonic humidifier) is needed. But later on as your products drop in moisture content, more and more humidity is needed to accommodate the drying process. This might sound unintuitive, i.e. more humidity needed, but the reality is that you have to slow down the drying process so the moisture can diffuse from the center of the product out to the edges where it can be drawn off. If you do not do this, case hardening is almost inevitable.

When I first started years ago, I also used a small computer fan to circulate air. But I also found that lead to case hardening so I stopped that. You might consider undervolting your fan so it is just barely turning, or maybe just switch it on for ~10 seconds per hour. I've just looked up the specs on fans like this, and they push around 50 cubic feet per minute during normal operation. So a 10 second pulse should easily take care of the 3.3 cubic feet volume of your minifridge.

More tightly patching up the 1.25" opening you made might make a small difference, but it sound like you have already done a pretty good job of that. So I think your main issue is what I mentioned above--that humidity drops drastically every time the compressor comes on to cool the unit.

The above is all based on my own personal experience. I do not think that a dehumidifier is needed for these small chambers, indeed, the main issue is making sure that humidity stays high enough that the drying process is slow and continuous so as to prevent case hardening. Whatever the case, your (and others) experience may be different so good luck with the effort!

Ah, here's the temp-humidity plot from the beverage cooler that I mentioned earlier:

 

[Mmmm Meat]

In my own experience using a small refrigerator (3.2 cubic feet like yours) and a slightly larger beverage cooler (4.4 cubic feet), the issue has never been the need to remove humidity, but the need to supplement it to prevent case hardening. Because these small devices hold a very limited volume of air, as soon as the compressor kicks on to cool down the unit, the humidity is instantly drawn to the coils, which dries out the ambient air to such a degree that it promotes case hardening. I attach a temperature/humidity plot from the 4.4 cubic feed beverage cooler during a drying run so you can see just how tightly the two are coupled.

The stage of your drying process also makes a huge difference--earlier on in the drying process, when your products still have lots of moisture, less added humidity (by the ultrasonic humidifier) is needed. But later on as your products drop in moisture content, more and more humidity is needed to accommodate the drying process. This might sound unintuitive, i.e. more humidity needed, but the reality is that you have to slow down the drying process so the moisture can diffuse from the center of the product out to the edges where it can be drawn off. If you do not do this, case hardening is almost inevitable.

When I first started years ago, I also used a small computer fan to circulate air. But I also found that lead to case hardening so I stopped that. You might consider undervolting your fan so it is just barely turning, or maybe just switch it on for ~10 seconds per hour. I've just looked up the specs on fans like this, and they push around 50 cubic feet per minute during normal operation. So a 10 second pulse should easily take care of the 3.3 cubic feet volume of your minifridge.

More tightly patching up the 1.25" opening you made might make a small difference, but it sound like you have already done a pretty good job of that. So I think your main issue is what I mentioned above--that humidity drops drastically every time the compressor comes on to cool the unit.

The above is all based on my own personal experience. I do not think that a dehumidifier is needed for these small chambers, indeed, the main issue is making sure that humidity stays high enough that the drying process is slow and continuous so as to prevent case hardening. Whatever the case, your (and others) experience may be different so good luck with the effort!

Ah, here's the temp-humidity plot from the beverage cooler that I mentioned earlier:

View attachment 487308

Thank you for your detailed response. Clearly your discussion matches your data but I have difficulty correlating your findings with what I was seeing a couple days ago. It may be that my numbers are way out of normal range because there is no product hanging in the chamber, but I was having trouble keeping the humidity under 80% - often it was up in the 90's when the ambient RH was high. It may be that the wild RH swings downward to the low 50% range were due to the fridge cooling cycle, though I found that if I didn't use the dehumidifier, I didn't see any downward swings in RH during cooling that I noticed. I'll try and take all this information and play with it once the second humidity controller arrives.
In the mean time, I got my (new) replacement sausage stuffer today and cut up a pork shoulder roast, started a cure on a Capicola and made 5 pounds of fresh garlic sausage. I've got two weeks to figure out the curing chamber before the Coppa goes in to hang.
Again, many thanks for your help and suggestions.

 

[Beaverdam213]

Thank you for the book selection. I'll get that one for sure. I think that I may have seen your recommendation for two controllers for humidity elsewhere on a different thread. I was considering this option, though I thought I'd ask before buying. The wife is already questioning my purchases to date. I'll have to hide this one from her.

I saw a different suggestion regarding use of a bowl of sodium chloride/water solution to maintain humidity at 75%. Is this a functional idea that would work when meat is in the chamber too?

Thanks!

that’s what i did. i use two fans...one blowing in at bottom and one blowing out at top...then just some jars with salt water in them. i used a sensor that kicked on the fans when it got too humid.

 

[Mmmm Meat]

that’s what i did. i use two fans...one blowing in at bottom and one blowing out at top...then just some jars with salt water in them. i used a sensor that kicked on the fans when it got too humid.

I take that as you cut two holes for venting in/out. I couldn't decide whether it was a good idea to open the chamber up to constantly being exposed to external conditions.....

 

[Mmmm Meat]

Thank you for your detailed response. Clearly your discussion matches your data but I have difficulty correlating your findings with what I was seeing a couple days ago. It may be that my numbers are way out of normal range because there is no product hanging in the chamber, but I was having trouble keeping the humidity under 80% - often it was up in the 90's when the ambient RH was high. It may be that the wild RH swings downward to the low 50% range were due to the fridge cooling cycle, though I found that if I didn't use the dehumidifier, I didn't see any downward swings in RH during cooling that I noticed. I'll try and take all this information and play with it once the second humidity controller arrives.
In the mean time, I got my (new) replacement sausage stuffer today and cut up a pork shoulder roast, started a cure on a Capicola and made 5 pounds of fresh garlic sausage. I've got two weeks to figure out the curing chamber before the Coppa goes in to hang.
Again, many thanks for your help and suggestions.

Oh - I forgot about the fan issue. What I originally did was put the fan inside a cardboard box with just a couple smallish holes cut into each side of it, which restricted airflow to probably 5 - 10 percent of a fully exposed fan. I could imagine it might overheat if it ran for long periods like this - maybe. The box was pretty functional though - I could hardly feel any air movement at all, so I think it would be OK like that, but with a plastic box instead of cardboard. I can imagine cardboard becoming a sludgy mess in no time at all with 80% humidity and the salami mold nearby.
I also considered a second rheostat run in series with the first, which I think would reduce the fan speed another 75 percent or so.
What I finally decided on was a repeat cycle timer I found on Amazon that can be set to repeating and short interval switching on/off, I could conceivably run the fan for 10 seconds per hour (for example). If that worked as advertised, then it sounds very workable. The downside - the unit cost like $26 for a little black box that may or may not be as accurate as advertised. I'd rather have the $26 bucks in my pocket so I'm not opening the packaging on that unit till I try other less expensive methods. It's a lower priority issue at this point.

 

[verbage]

Clearly your discussion matches your data but I have difficulty correlating your findings with what I was seeing a couple days ago. It may be that my numbers are way out of normal range because there is no product hanging in the chamber, but I was having trouble keeping the humidity under 80% - often it was up in the 90's when the ambient RH was high. It may be that the wild RH swings downward to the low 50% range were due to the fridge cooling cycle, though I found that if I didn't use the dehumidifier, I didn't see any downward swings in RH during cooling that I noticed.

Yes, yes, my comments are based on my own experience with my particular setup/environment--I have no doubt that you are seeing what you are seeing! And for sure, the product you have drying in the chamber is an active participant in moderating the humidity, and the drying process, in general. So I think you are right in suggesting that the high variability you are seeing is probably due to having the chamber empty.

I've been thinking about this, and there are a couple of big differences between our setups that probably explain the humidity differences. With the beverage cooler, the cooling element is a vertical panel at the back of the chamber, and after moisture accumulates there as ice, when it melts, it drips into a channel that is routed to the outside of the unit. So sort of like a "frost-free" unit, there is some mechanism for physically removing the moisture from the chamber. In the case of the minifridge, ice will accumulate on the freezer compartment element. But then there is no way for it to get out of the unit unless it is physically removed as an ice cake or in a drip pan. Or unless one makes modifications to the unit like for air exchange, or adds another element to the system like a dehumidifier.

I am now wracking my brain to remember my observations from early on when I was using a minifridge before swapping to a beverage cooler. I am pretty sure that I had to physically empty the drip tray once in a while. And so that would have been a constant source of humidity. I do remember that is when I tried adding a 12v computer fan, but undervolted it to run slower with a 5v USB adapter. But that is also when I noticed the case hardening, and stopped using a fan. I did not modify the minifridge with air exchange holes--I just had the fan running slowly for continuous circulation within the chamber.

One other potential big difference that I can think of--my drying chamber is in my house, which has central AC/heat. So as humidity in the house is pretty well-controlled, the chamber has pretty consistent environmental conditions. If it were in my garage or basement, well, the external environmental conditions would be very different. For example, in a hot garage, the compressor would probably be cycling much more frequently to maintain temperature, and that might exacerbate the potential for case hardening.

 

[verbage]

What I finally decided on was a repeat cycle timer I found on Amazon that can be set to repeating and short interval switching on/off, I could conceivably run the fan for 10 seconds per hour (for example). If that worked as advertised, then it sounds very workable. The downside - the unit cost like $26 for a little black box that may or may not be as accurate as advertised.

I'm not sure how adventurous you are, but if you feel comfortable with basic electronics and some basic computer coding, you could use a simple relay and microcontroller (like an "Arduino") to trigger your fan for a 10 secs/hour cycle very easily (or any other type of cycle you want). Parts for this would literally be <$5 if you don't mind ordering them from China, and maybe even the same price or just a few bucks more via eBay. I can provide some guidance if interested.