Let's talk curing chambers

I've received many many emails asking about specifics of my curing chamber, and more specifically about using different types of refrigerators to use as a curing chamber, so I wanted to post some quick information on choosing a fridge.

The general idea when we're turning a fridge into a curing chamber is that we want to control temperature, through a temperature controller, and humidity, through an ultrasonic humidifier and a humidity controller. In order to do this the fridge has to run "dry" so that we can add moisture back to the level of our choice, generally 70%-80%.

Easy enough, right? Well, sort of. Most normal, large, kitchen refrigerators, run "dry". Basically, they work by blowing air over a cold evaporator coil, and direct it into the fridge. Since the evaporator coil of a fridge is rather chilly, the moisture in the air condenses out, and the air that ends up in the fridge is very dry. At the same time the water which condensed out of the air onto the evaporator coil freezes and needs to be melted off periodically and directed out. This is exactly what a "frost free" fridge does. Every 12 hours a small heater wire melts the ice which forms on the evaporator coil and the water is collected and directed out to a pan where the water can evaporate back into the environment. So, in the end we have a "dry" fridge, which on it's own would normally run somewhere around 20-40% RH, we add humidity back in and control temperature, and voila'! curing chamber.

The questions arise when people start wanting to use standup freezers, chest freezers, or compact fridges such as the ones used in dorms or wine refrigerators (since they conveniently run at temperatures suited for what we need) or some other kind of system for their curing chambers. The two most common questions about fridges are in regards to wine fridges and compact refridgerators, and whether they can be used. The simple answer is.... sort of. Let me explain.

All the compact and wine fridges I've see have one thing in common which makes them very different from the standard fridge I recommend for curing. They cool not by blowing air over an evaporator coil but by cooling the fridge directly via a cooling plate inside the fridge; just a metal plate with channels in it in which the refrigerant runs. You can often see the metal plate at the back of the fridge, or if the compact fridge has a "freezer" section at the top, that's what cools the fridge. The problem with these is that the cooling plate does work to cool the fridge, and it does condense the water out of the air (remember we want a "dry" fridge so we can rehumidify) but the water isn't removed from the refrigerator section, at least not very well. The water condenses out; some does drip away into a collection tray, but most re-evaporates right back into the chamber, so we're back where we started.

Wine fridges generally cool using the same principle, at least the ones I've seen, they use a cooling plate inside the refrigerator section.

The bottom line is that these compact refrigerators, from what I've seen,  have no good way of extracting moisture from the air and keeping it out, which means when you put meat in there to lose water, the moisture loss has no where to go, and ends up making the fridge more and more humid as your products dry.

Are there ways to get them to work? Sure, there are, I haven't given them much thought because I haven't had to. You'd have to figure out a way to dehumidify to a specific level. If you want to try, give it a go, but I have to tell you I'm not sure how to do it, so...sorry! I know for example, as I've said before one can buy beads and sheets which absorb and release moisture to maintain a humidity of choice, or that a tray of wet salt will maintain about 75% RH. I have no idea how effective these things are though and how fast they actually work.

What about standup freezers? Well, looking at my standup freezer, it does look like it would work. Mine doesn't have a cooling plate, it blows cold air in through a vent, so I have to assume there is an evaporator plate somewhere cooling that air before it gets to the freezer ( add to that that it's a frost free freezer and i'm even more sure about that). But, i have never measured the RH in there and I don't know how it would do or what it would do running at 55 deg. F.

How about beverage fridges with nice sliding glass doors? Well, I know that Scott at Sausage Debauchery has successfully converted one of those, but I don't know how he did it. I do know that he was pulling his hair out for a week to get it to work properly.

How about chest freezers? I don't know, I don't own one so I don't know what cooling method they use.

I'm sure there are 100 different types of refrigeration systems, and I cannot possibly know if every one will or will not work. The first questions you should ask yourself is "Does this fridge have an evaporator coil outside the refrigerator section which will dry the air before it blows into the fridge"? If the answer is "Yes", then the fridge SHOULD work. If it doesn't, well, you're on your own to figure it out:)

Good Luck!