Temperature Control

Following my series of posts about my curing fridge Nate asked for a picture of the inside of my control box. Regrettably, as the box is home-made it's screwed together with wood-screws and is difficult to take apart. The picture below is of a control box set-up for temperature control which was assembled by a good friend of mine; it's how it looks when made by a professional.

Inside a Temperature Control box

Converting a Fridge into a Curing Chamber - Part 3 - The Electrics

Having assessed the problems in Converting a Fridge into a Curing Chamber - Part 2 - Controlling Humidity, and acquired the necessary thermostat, hygrostat(s) and relays, there now comes the dreaded time when it all has to be wired together!

My own control box has a thermostat and two hygrostats. There are double plugs controlled by each of these, plus one for normal usage:

Original Wiring for curing fridge / chamber

Whilst I am happy to supply details of the wiring, it's like an explosion in a spaghetti factory, so it's maybe best to look at each element separately!

Obviously, these diagrams are specific to the products I've used. Details of these are in Part 1 and 2 of this tutorial. However, they give a good idea of what's involved and may assist in working out the detail for your own choice of controller. Often the instructions and wiring diagrams supplied by the manufacturer are confusing, and sometimes, not even in English!

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Converting a Fridge into a Curing Chamber - Part 2 - Controlling Humidity

At the end of Converting a Fridge into a Curing Chamber - Part 1 - Controlling Temperature we'd just acquired a hygrometer to check the humidity in our fridge now that we've got it running a 12°C...

...The chances are that the humidity's not at the level we want, but before we start to do something about it, let's just look at what relative humidity is.

When we refer to humidity in percentage terms, what we are referring to is the percentage of moisture in the air, relative to the maximum that the air can hold, at that temperature. Warm air can hold a lot more water than cold air before it becomes saturated, so air at 20°C with 100% relative humidity (RH) will have a lot more moisture in it than air at 12°C with the same 100% relative humidity. Let's make that 'doubly clear': if we cool air, the relative humidity will increase, even though the amount of water in it won't change. This means that the relative humidity of any air we introduce into the fridge will increase as it cools.

Hourly weather statisticsPlaces with different ambient humidity will require different solutions to the problem; the dry of the desert is very different to the wet of the rain-forest.

Don't think that things will be easy because the UK has a temperate climate. Take yesterday as an example: at 7am the relative humidity was 100%, but by 6pm it was only 38% (click the image on the right to see further details). For this reason, control of humidity by the introduction of fresh air using a fan, is unlikely to work here, even though it does in climates with constant low humidity.

So what do we do to control the relative humidity? Well, I suggest that you do absolutely nothing! Instead, go and make some chorizo, or any other salami type product that's fairly thin. Don't spend a lot of money doing it though; it may become a sacrificial sausage later! "Why?", I hear you ask. Well, experience has taught me that drying chambers with salami in them behave very differently than empty ones. Using your fridge to make some salami will give a truer indication of how the humidity will behave.

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Converting a Fridge into a Curing Chamber - Part 1 - Controlling Temperature

lomo dryingAlthough it's a common topic of discussion on the sausage making forum, I've never got around to writing about converting my fridge into an air-drying chamber. Before I start, I accept no responsibility for what you do with the information here; it's up to you to ensure that what you do is safe and complies with any relevant regulations/legislation. If in doubt, please seek the advice of a professionally qualified person.

This information relates to converting a fridge for use in the UK. For details of converting a fridge in the US, please see this article on the Cured Meats website.

Firstly, let's look at the conditions we need; there are 3 main phases during the process of making air-dried products, curing, fermentation and drying. Ideal conditions for these are:

  • Curing - normal fridge temperatures are fine, ideally at the higher end around 5° - 8°C.
  • Fermenting - used when making sausage and occasionally with dried meats. The product is held at temperatures around 24°C with a very high relative humidity, around 90% - 95%, for a period that can vary from 12 hours to several days, to enable bacteria to make the sausage more acidic, which makes it safe to eat. The exact temperatures and times depend on the specific bacteria added, so follow the manufacturers guidelines or the recipe carefully.
  • Drying - a period of weeks, or months, during which we want the product to dry slowly and evenly which will add to its safety. The conditions for doing this are ideally between 10° - 15°C with a relative humidity between 70% and 85%. Our aim is to keep the humidity of the chamber just slightly below that of the product, whilst it dries. Regular changes of air are also beneficial. My own experience, along with that of fellow home sausage-makers, suggests that there are less problems when the drying is takes place at the lower end of this temperature range. Many favour a temperature of 12°C, or thereabouts, as do I.

Most people have little problem creating the conditions for the first two phases, but often have problems with the third; modern houses tend not to have places with these conditions. A cellar or pantry is often ideal, or can be adapted easily. If you can beg or borrow the use of one, then do so: the larger the area, the easier it seems to be to control. However, for the rest of us, the only economic option is to adapt a fridge or freezer to create the conditions required.

Firstly, you'll need a fridge to convert - frost free is the type to go for as these tend to have very low humidity; it's easier to increase humidity than decrease it!

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Air Drying Meat - Equipment

Air drying Fridge

Posts have been pretty scarce around here lately. It's not that I've not been doing things; just that I haven't got around to writing about them.

The redesign of my 'drying' fridge has taken up a lot of my time - mainly because I'm not very good when it comes to anything that involves DIY skills! However, it's up and running again and although it will need a further modification (to remove a large dehumidifier that's inside it), it's working well.

The major change has been to install digital rather than analogue controls; they're far more accurate. I've also installed two humidity controls so that I can set the humidifier and dehumidifier to run independently. Designing the control box was a kerfuffle, but with the help of my friendly neighbourhood electronics expert (a friend with his own electronic controls company), I have finally got my head 'around' relays and other such electronic gizmos. The controls are now also housed in a wooden box kindly made for me by a neighbour. It still needs a coat of paint but that can come later:

Drying fridge control box

It's seen here running at high temperature (23°C) and humidity (82%) during the fermentation stage of a Genoa type salami. I'll post the recipe and method when I see how they turn out.

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