Comparative Relative Humidity Table

[onewheeler]

Another interesting back of envelope calculation is that at around 80% RH and 12- 13 C -ish temperature, the air contains roughly 7 g / kg water. So, in your hypothetical 'fridge, there's around 1 g of water vapour. If you want to lose, say,1 kg of moisture from 3 kg of sausage (30% weight loss or so) that implies you'll need around 1000 air changes.

Might as well leave the door open!

[kimgary]

Hi

It maybe worthwhile fittinga small fan into a domestic unit to exhaust the air, say every 4 hours by a timer, within a reasonable temp and RH range for the new incoming air the refrigeration unit should be able to keep reasonable temp and RH.

At only six air changes a day 1000 air changes will only take 166 days, not long in the curing times.

If we go back to nature and look at a ham hanging in Italy in the hillsides we would see a vast amount of air at a steady temp and RH, the breeze blowing over the ham will pick up the evaporating moisture and take it away, the moisture from the ham cannot affect theRH, the next bit of breeze a split second latter will be at the same temp and RH and the breeze is the "vehicle" to remove the moisture.

In a domestic set up the evaporation from the ham would soon alter the RH within the confines of the fridge, in a commercial unit the volumes are much larger and the circulating moisture is condensed out.

I have the utmost admiration and respect for the people that manage to cure in their homemade units and look forward to trying it when I can, it must be cheaper than moving to Italy.

Thanks to Phil for starting another good talking point, I think someone on here uses the quote "no one knows more than all of us" we are all striving to produce something that very few people will ever try and by talking and sharing we will reach our goals.

Regards Gazza.

[grisell]

Another interesting back of envelope calculation is that at around 80% RH and 12- 13 C -ish temperature, the air contains roughly 7 g / kg water. So, in your hypothetical 'fridge, there's around 1 g of water vapour. If you want to lose, say,1 kg of moisture from 3 kg of sausage (30% weight loss or so) that implies you'll need around 1000 air changes.

Might as well leave the door open!

That would be true in a confined space without a refrigeration machine. In a fridge, you are forgetting about the condensor's removing of moisture!

I have had successful drying and weight loss during one week without opening the door once.

[kimgary]

Interesting André,

Do you mean the evaporator?

If you are referring to the plate at the back of the fridge then this is the evaporator however if you have your fridge running via a temp controller at about 13°C then the evaporator is rarely going to get cold enough to form frost, defrost and hence remove moisture from the cabinet?

If you were trying for a cabinet temp of 13°C with a ambient temp of 25°C + then obviously this would change, same as 1-3°C with ambient above 16°C

Regards Gazza

[grisell]

Yes, I mean the the plate at the back of the fridge. It shouldn't need to be ice-cold. If it's colder than the environment, vapour will condense. Not all of that condensed water will get vapourised again, so there is a net deficit of humidity. If I'm thinking right, that is ( ).

[wheels]

High Phil

Some figures for you to think about:-

I don't wish to get into point ).00000000etc so will round about figures.
Air at 10°C - 1Kg will have a volume of 1.2m³

Large fridge at 200 litres is 1/6th of 1.2m³ therefore 1/6th of kilogram of air in that space weighs 166grams.

Ok, difference in water weight per kg air from 12°c @75%RH to 15°c @75%RH is 1.4 grams, divide by 6 equals 0.2 grams/cc of water difference within the confines of the chamber, not a great difference.

An interesting observation.

However, we could do the same calc for air at 12°C at 50% RH and air at 75% RH (at the same temperature) and obtain similar results, but we know that there would be a major difference in the way the sausage would dry, the potential for case hardening, and how moulds would/would not grow.

I don't have the scientific knowledge of some if you guys, so I'll leave you to decide what that means.

Can I say, though, how good it is to be discussing these sort of subjects again.

Phil

[BriCan]

Equally one could imagine a case where the temperature was very low and an equally high rH. In this case, there's be little or no mould formation, while again there's be no evaporation from the surface, so case hardening would be virtually impossible too.

Depending on the temperature and humidity (20 - 25 degrees C with 65% humidity) depends on the length of time we leave product in the drying room, When firm to touch/feel we transfer to cooler which runs at 1 - 4 degrees C with humidity between 70 - 80% Defrost cycle raises humidity and temperature during the course of a day. no case hardening that I have seen and for mould all I ever see is good mould.

I do realise that my situation is a lot different that most home owners but saying that I could use my workshop which is part of the house most of the year with very minimal alterations.

[BriCan]

Another interesting back of envelope calculation is that at around 80% RH and 12- 13 C -ish temperature, the air contains roughly 7 g / kg water. So, in your hypothetical 'fridge, there's around 1 g of water vapour. If you want to lose, say,1 kg of moisture from 3 kg of sausage (30% weight loss or so) that implies you'll need around 1000 air changes.

Might as well leave the door open!

That would be true in a confined space without a refrigeration machine. In a fridge, you are forgetting about the condensor's removing of moisture!

But surly one has to remember that all refrigeration units do a defrost cycle 2 - 3 times a day and thus this will put moisture within the unit

[onewheeler]

Of course the condenser will take out moisture, but how much depends on how often it runs.

Having commissioned my curing chamber / fridge in the garage recently, it's become obvious that a little more complexity than a simple temperature controller is needed. I first powered it up in the summer, and the internal RH (at a nominal 11 C) seemed fairly settled at about 80%. It was recently loaded with a batch of chorizo, and the RH refused to drop under 90%, whether the door was opened a (large) crack or not. The conclusion was that the ambient temperature has dropped since the summer, and the 'fridge hardly ever comes on. So, I inserted a length of trace heating tape - about 30 watts worth. The 'fridge now comes on regularly, and the RH has settled at something centred around 70 - 75%.

One might conclude that for a curing cabinet located in a garage (as opposed to a nice, warm apartment) there are three regimes of operation:

Summer, when the 'fridge operates normally and the condenser takes the RH down

Autumn when ambient temperature is close to the desired temperature, and some heating is needed to make the 'fridge go into cooling mode

Winter when some heat needs to be applied and probably some forced ventilation will be needed

The next job will be to play with the amount of heat added as 30 watts is probably more than needed.

Martin/