Cooking with Stored Heat - Hay Box; Vacuum flasks etc.
| 09 January 2010
Vacuum (Thermos) Flask Cookery
For less than $15 at your local supermarket you can invest in a wide-mouth thermos flask that holds 500 millilitres or hot foods. If you want to pay more you can get bigger units or the more robust stainless steel ones. All of them can be used to cook food using the stores heat as well as to keep precooked food hot. Into your flask put grains such as rice, wheat or pearl barley, some dried beans , any fresh vegies (diced first ), any meat that you want to include and, allowing some space for expansion, fill with water. Then tip the contents of the flask out into a saucepan and bring to the boil, boil it for five minutes to drive the heat into the centre of the grains and the beans. Next pour the mix into your thermos and put on the cap, then put it aside in a draught-free area for eight to ten hours. When the time is up open it and add a few herbs, spices or sauces, and you have a hot, tasty, home-cooked meal with a minimum of energy consumption. It might need to be tipped into a saucepan and brought back to the boil if it has to be left any longer, but in a thermos it is impossible to overcook.
The ingredients you have depend upon the bits and pieces you have left over; this style of cooking lends itself to improvisation. A hot breakfast can be made by following the directions using just dry wheat which can then have milk and sugar added to it in the morning to give a cheap, hot feed (even if it does corner the market on bland!). It is worth having a thermos flask for each member of the family.
The Hay Box – General Processes
This is similar to, but a much older idea than, the vacuum flask, where a pot or saucepan is first preheated then placed in an insulated box to cook in its stored heat. Cookers of this type were in widespread use in Europe in the middle of last century and in America early this century, but their use seems to have declined after World War 1. The hay box cooker consists of three parts: the outer container, insulating material placed inside the container, and the pots in which the food cooks.
The outer container can be a Styrofoam Esky or recycled broccoli box, an old trunk, wooden box or barrel, in fact any container that is large enough to hold the pot and insulation and is airtight. Wooden boxes or barrels with cracks between the slats or staves will need to be lined with cardboard or aluminium foil to ensure they are airtight. If the material of the box is also a good insulator such as Styrofoam, so much the better. The insulating material could be hay or straw as it was in the originals, or crumpled up newspaper, Styrofoam beads (eg.bean bag filling) foam rubber or sawdust, depending on what is available. Materials such as the straw or newspaper can be used as-is but the Styrofoam beads or sawdust tend to spread all over the place unless confined in a fabric cover similar to a pillowcase. Also, to make its removal easier, the insulation material destined for use on top of the pot should be sewn into an insulating cushion the same size as the top of the container.
The pot should also be made of a material that retains its heat well, such as Corning Ware, heavy stainless steel, well seasoned or enamelled cast iron, or stoneware. It also must have a tightly fitting lid so that the steam and heat which does the work is not allowed to escape into the box. To achieve the best results it is important to ensure that the pot is full or almost full of food so that the heat will be retained long enough to cook the food fully.
To use the cooker, the pot plus food must be boiled on the top of the stove so that all ingredients are hot in the centre, thus the denser the food or the larger the chunks the longer it takes. Dried beans should be soaked overnight before boiling, large cuts of meats simmered for one-fifth of their normal cooking time. Once the food is preheated the lid is put on the pot and the whole assembly, wrapped in a paper bag or newspaper, then a tea towel, then nestled down into the insulation, the cushion placed on the top and the lid securely closed.
How long the food needs to be left to cook varies with the type of dish and its ingredients but five to eight hours is a good start. However once it’s in the hay box no peeking, it lets the heat out. If, on inspection, the food is not quite cooked it should be re-boiled, rewrapped and then returned to the hay box. When the food is cooked it should be re-boiled before serving. Crock pot recipes can be easily converted for use in the hay box .
After each use the hay box should be pulled apart and aired to prevent any build-up of bugs and odours, especially if the insulation is of organic origin. Insulation of organic origin will also need to be replaced from time to time if the hay box is in regular use, due to deterioration caused by such bugs.
The Haybox – How I made mine!
I first tried making one out of straw, a pine box and a large glass casserole dish but it was not really successful. The main problem was that the casserole dish was too large so that you had to make too much food in one go, and there was not enough insulation between the casserole and the side of the wooden box. So I until recently I had gone without one of these useful devices.
Christmas (2002), while wandering through a neighbours garage sale I spied a large plastic esky, it looked well used, but it was intact and BIG (590mm x 370mm x 420mm high), so for the princely sum of $5 it was mine! To turn it into a haybox cooker I then needed to work out what cooking pot/s to use what and insulation material to use.
Cooking Pots
I needed to work out the type of cooking pots to use, I had decided that the size of the esky would allow me to use two pots – a one litre and a two litre pot – so that I would have some flexibility depending on the number of people to be fed. The haybox cooker works most efficiently when the cooking pot is almost full of food.
Another way to improve heat retention is to ensure that the cooking pots have the least possible surface area for the volume contained, this is a sphere – which is geometrically inconvenient for my purposes, so I settled on a couple of squat, enamelled steel billy cans. The lids of the cans also have a rim which ensures that condensation on the lid is returned to the pot.
The enamelling on both pots is a dark blue and the idea was that I could use my solar oven to heat up the food and then put it into the haybox cooker to complete the process. That was the theory and for the 1 litre pot it works fine, but I found that when I tried the 2 litre pot it is just a wee to big, and prevents the glass front from entirely closing, which in turn lets the heat out. Another fine theory blown to hell due to lack of attention to detail!
Insulation
The obvious answer here was “hay”, being a traditionalist of sorts, but hay has some disadvantages in that it is not so effective an insulator as some modern materials and it tends to absorb steam and odours during the cooking process which then cause it to grow bugs (yuch!). I wanted something that was light, low maintenance and an effective insulator. As luck would have it, a friend offered me an 1800mm x 900mm sheet of polystyrene foam that was 25mm thick and had been used as packing in a container, so I accepted it gratefully.
I still needed to cut it to shape and the classic way using a saw creates a hell of a mess with fine particles of polystyrene all over the place. So rather than do that I looked around to see if I could get hold of hot wire cutter, which makes a nice smooth cut with little or no little fiddly bits. After some searching I found a reasonably priced ($25) battery powered unit available from Hobbyco in the city (Sydney). Its limitation was that it could only cut polystyrene sheet up to 35mm thick so this was not much of a problem with my stuff being only 25mm thick.
I cut two slabs to act as the bottom insulation and then a number of strips with holes in them to accept the cooking containers up to the level of their lids. Here the analogy breaks down! To use the rigid polyester foam over the tops of the cooking containers by carving out the correct size and shape was beyond my technology, so I remembered our family motto - “when all else fails – cheat!”. I bought some polystyrene beads, used for stuffing bean bags and made up a cushion by loosely filling an old flannelette pillowcase, which sits neatly on top of the cooking containers and acts and an insulator. I sewed the pillowcase closed, because anything less than an airtight seal and the beans escape and get EVERYWHERE!
One problem with the esky was that, in common with a lot of esky’s nowadays, there is actually no insulation in the formed plastic top, I assume that the air gap in the lid is supposed to act as an insulator. I was not happy with this, so using a cut of funnel I persuaded a whole stack of the polystyrene beans to go into a moulding hole in the top. That was one tedious job, because the beans clearly did not want to go into the lid! Anyway once completed I sealed the hole with an (unused) industrial ear plug.
The haybox cooker was now completed.
Operation
The idea is to load up the cooking pot with your food in the same way you would a crockpot, this style of cooking lends itself to soups, stews and casseroles ie wet cooking so if you are after dry or crisp, this is not the way to go. Having filled your pots with ingredients and water up to about 25mm from the top, put it on the stove and bring it up to the boil, and boil for five minutes to get the heat into the centre of any larger lumps of ingredient. Once it has been boiling for 5 minutes quickly transfer it to the haybox cooker, smooth down the insulating pillow and clamp on the lid.
Leave everything undisturbed for 8 to 12 hours (No peeking!) and then open for a hot deliciously cooked meal.
To test our haybox cooker, I filled both containers and boiled them, transferring them straight to the cooker and then sealed it up. Early the next day, about 10 hours later, the 2 litre pot was still over 90°C and the 1 litre one was still above 85°C. The haybox cooker has served us very well, particularly during winter and I even used it to make a batch of my beef and veggie soup, a family favourite. I still looks a bit basic and I want to make a nice wooden box to go around it so that it looks like a piece of furniture rather than a well used esky…………………..eventually!
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