Stalking the elusive RH

[porterdriver]

I have a curing chamber that I am building out of a frost-free Kenmore freezer.  I thought that way I would have a whole cabinet to work with instead of the traditional split that is found in most refrigerators.

The temperature is controlled by a Johnson Control line-voltage thermostat.  It is capable of controlling temperatures via line voltage from 10-120 degrees (F).  It is currently set at 45 degrees (F).

The humidity is controlled by a Green Air Products THC-1 line voltage humidistat running a small Crane humidifier.  The humidifier is set to its lowest setting and the humidistat is set to 60%.

For monitoring I have two thermometer/hygrometers (for redundancy or confusion, I'm not sure which).  One is the Extech Instruments 445715 which has had the hygrometer already calibrated.  It has a probe that is inside the freezer with the temp/RH display on the outside.  The other monitor is an Acu-Rite 00592W3 that has a remote sensor which cannot be calibrated but is supposed to be +/- 5% on the RH.  The remote sensor is sitting on a shelf inside the freezer at the same level as the sensor for the Extech.

I am logging the temp/RH from both monitors throughout the day.  Both thermometers seem to be in close agreement with the Acu-Rite reading around 1 degree (F) lower than the Extech. 
However, the humidity seems all over the place.  The Extech, which I believe is supposed to be more accurate (after all I did calibrate the thing) swings from 43% to 99%.  The Acu-Rite (after about 24 hours in the freezer) has been reading very accurately between 59% and 61%. Both devices have been in for the same length of time and the door has not been opened.

I told you all this to ask these simple questions.  How critical is the cabinet humidity, especially in terms of the two sets of readings?  I get the sense the Extech is giving me instantaneous readings while the Acu-Rite is giving me an average?  Is that a safe assumption?  Is this setup sufficiently accurate for curing meats, sausages, hams, etc.?

Thanks for listening to the ramble and I look forward to this group's advice.

[NePaSmoKer]

Try to get as close to 70% R/H as you can. You want to reduce the green weight of the meat.

[porterdriver]

I picked 60% arbitrarily.  I was just mostly interested to see how this contraption worked.  I have bumped the humdistat up to 70% per the, always, sage advice of NePaSmoker.

I still would like some insight on the tracking RH, types of hygrometers (benefits and liabilities), and how much "swing" is acceptable in the RH while trying to target a specific figure.

Thanks

[devo]

Here is a link with some good info. You might find the answer in it.

http://forum.bradleysmoker.com/index.php?topic=21853.0

[Habanero Smoker]

I like to keep my cabinet between 60% -  65% RH, but that is almost impossible for me. As you observed when the freezer cycles on to cool the cabinet, the RH falls, when it is off moisture from the sausage causes the cabinet RH to rise, and will go into the 90's. I would put more trust into the Extech. I have that model. It is extremely accurate, and fast reading. I also have an Oregon Scientific wireless that reads much lower than the Extech, and takes much longer to register the temperatures.

If you don't have a vent to outlet the humidity, depending on how much sausage and/or meat you have drying you may find that you do not need a humidifier, but may have to open the door frequently and fan the air to get the humidity to drop. Too high of a RH makes you prone to bacteria growing on the outside of the sausage, and slows the drying process down so you need to watch for that and "wash" the sausage with either a salt brine, or vinegar solution, when needed. As long as you don't go below 55% for too long of a period, you don't have to worry about the outside casings hardening. Which can cause the inside of the sausage to stay moist and spoil.

I would also set the cabinet temperature higher to around 55°F - 60°F; 60°F being the ideal.

[porterdriver]

Thanks for the insight Habs.

I'm still unsure how to interpret the data that the Extech is giving me.  I had (and you confirmed it) a sense that it was much more accurate than the Acu-Rite.  The Acu-Rite takes about 24-36 hours to stabilize on a RH change (about 12-24 on a temp change). but it fluctuates little once it gets settled in.  This, at least, give me an idea of the 'overall' RH in the cabinet.  How do you interpret the Extech to know that you have the right 'overall' RH?

Thanks.
Porterdriver

[Habanero Smoker]

The RH that is displayed on the instrument is the RH that I go by; it's just a monitoring tool to let you know if adjustments need to be made. For me I like to keep the cabinet RH at 60%; if the RH is over 80%, I need to bring it down. Since my cabinet is not vented, I have to open the door and fan until the RH drops. I do have a small dehumidifier but I haven't been able to try it out. If it drops below 60%, then my humidity controller will turn on. I found that I only needed the humidifier towards the end of the drying period.

You will see fluctuations in the RH as the freezer cycles on/off to maintain your set 45°F temperature. Most sources recommend that you use a cabinet temperature of 55°F - 60°F. Also if you raise the cabinet temperature to 60°F the freezer will cycle on less.

If you want to see what is happening during a period of time, you may want to invest in a data logger. Data logger will register and store the humidity and temperature data. You can set the time intervals you want the logger to record; such as hourly, every 6 hours, daily etc. Then you retrieve the logger, plug it into a USB port to down load the data. Most logger will output your data to either display in chart and numeric form. You can purchase them from $30 on up.

[porterdriver]

OK, Habs.  I just purchased a Lascar Electronics EL-USB-2+ data logger.  I will track temp and RH for a while and I'm sure I will be back with some questions.  But again, thanks for the guidance.

[Habanero Smoker]

That looks like a nice piece of equipment. I recently did  a search for data loggers, and many of the less expensive ones could not be found any more.

Be sure to ask any questions you have. There are a few of us that dry cure. Yesterday I was speaking with a chef that teaches a week long charcuterie class, and he says he won't tackle dry curing unless he has the proper equipment. So my suggestion is to start small, with 5 pounds of sausage and/or meat; 10 pounds maximum, until you learn how your cabinet functions and what you need to do to control the environment. My first project was over 20 pounds of sausages and meat, and I have a very difficult time trying to keep everything under control.

[porterdriver]

Habs,

Great advice.  I will go small until I get everything "dialed-in".

BTY, what are your thoughts on air exchange in curing chambers?  At this point I have no official air exchange in my curing chamber (except to open the doors periodically cuz I'm nosy).

[Habanero Smoker]

Air exchange makes every thing much more simple. The humidity controller you have will also dehumidify, but that particular model won't do both simultaneously; but it wouldn't be to hard to switch from one to another. It would just be a matter of unplugging one, plugging in the other, and toggle the switch to the appropriate setting.

If you had an air exchange you could hook you controller to the exhaust fan and switch it to dehumidify; and it would expel the moist air until it reaches your set RH. From my experience, you would not need the humidifier during the early stages of drying because the sausages and meats expels so much moisture.

I would love to have an air exchange, but I don't want to cut holes in my refrigerator, because I use it in the summer as a refrigerator to store food.

[porterdriver]

I saw a picture once of a converted refrigerator that had a louvered dryer-vent cover on the inlet and exhaust openings (inside refer and outside refer respectively).  That way when the fans kicked on the louvers would flap open. 

However like you, I don't want to lose the flexibility of my freezer and am not sure how much heat/cold loss there would be.

[Keymaster]

OK, Habs.  I just purchased a Lascar Electronics EL-USB-2+ data logger.  I will track temp and RH for a while and I'm sure I will be back with some questions.  But again, thanks for the guidance.

I use one of these at the indoor pool I take care of at work, they work well and track RH great. Sometimes we put it in the schools and hide it in the classroom so we can track temps for the complaining teachers that say their room is to cold. Then we can print out the report for two weeks and show them that their classroom has never dropped below 68° F for two weeks, that shutsem up real quick. The batteries are a little spendy, we get ours at Batteries plus.