Heat retention cooking has been around for a while, but is enjoying greater attention as people seek to be more economical and “green.” The concept involves bringing food to a boil for a specific amount of time and then moving the pot directly into a container filled with heat-retaining material, (like sawdust, hay, wool, or polystyrene), covering it, and letting the food sit for several hours. There are probably numerous ways to achieve this. Two that kept coming up in my Internet searches were a box design called the “wonder box,” and a (somewhat pricey) drawstring bag design called the “Wonderbag” that is being sold (http://nb-wonderbag.com/content/what-wonderbag). Both designs used cotton fabric and polystyrene balls, like those used in bean bag chairs. However, since I had read that shredded polystyrene packing peanuts could be used for the filler and I had an old partly cotton sheet on hand, I thought I would try to make one on my own. The instructions on how to make a wonder box were already on the Internet ( http://www.iwillprepare.com/cooking_files/Wonder_Box.htm ), but I was intrigued by the Wonderbag design (it looked a little simpler!) and decided to try to make one of those.
The first step was to obtain and shred the packing peanuts. I asked family members to save them for me, and I soon had enough—about five plastic shopping bags filled and tied off. I took the precaution of checking to be sure that they really were made of polystyrene and were not the new biodegradable ones that dissolve in water! At first, I was unsure of how to go about shredding them without making a tremendous mess, but after trying a couple options, I discovered that I could hold several peanuts between my two palms, insert both hands into a pillow case, and roll the peanuts between my hands until they broke apart. Any pieces that were still too large were gathered up and rolled again until they were small enough to resemble the balls that go into bean bag chairs. This kept most of the mess contained inside the pillow case.
Now that I had my filler done, I needed to make the bag to put it in. This meant designing my own Wonderbag-style pattern. I started by measuring the pot that I would generally use: a ten-inch-diameter pot about five inches deep. You can use whatever sized pot you like, but it must have a lid and not have a long handle. I placed the end of the measuring tape at the bottom edge on one side of the pot and went up the side and over the lid until I reached the center of the handle on the top. This gave me a measurement of eleven inches. I doubled this number and went to make a paper pattern of a large semi-circle with a radius of twenty-two inches. I used paper from an end roll of newsprint which I had obtained from the local newspaper, but several sheets of newspaper ads can be taped together to form a large enough sheet of paper to work with if other options are not available. The simplest way to get an even semi-circle is to anchor a pre-measured piece of string at the center point along the edge of the paper and attach a pencil to the other end. Keeping the string taut, trace an arc from one edge of the paper to the other.
As far as I can tell, the Wonderbag is formed of a center circle with separate sections radiating from it, so I began by marking a smaller semi-circle from the same center point as the larger one. I determined the size of this semi-circle by measuring the radius of the bottom of my pot and adding an additional inch. After I had drawn what would become the center circle, I got a protractor to help me in dividing the outside edge into five equal sections. Placing the protractor at the center point on the pattern, I made marks on the pattern at 36, 72, 108, and 144 degrees (I began on the right side in my photo!). Then I used a yardstick to draw lines on my pattern from the edge of the center circle to the outside edge of the paper. Now that the pattern was complete, I turned my attention to the fabric.
I needed to have a large enough piece of fabric to make two circles that were each forty-four inches wide. I knew the fabric needed to be fairly thin, and since synthetic fibers melt in high heat, I also knew that the fabric needed to be made of a natural fiber. I had a sheet that had been given to me that was probably large enough to have cut both circles from, but the fiber content was only half cotton and the rest was synthetic so I determined to use it for the outside of the bag only. If I had had access to forty-five-inch 100% cotton fabric, I would have purchased that, but the cheapest expedient to hand turned out to be another sheet that, while not 100% cotton, was a 60/40 blend. I decided to work with that. I folded both of the sheets in half and placing the pattern with the straight edge on the folds, cut through all the layers. This gave me the two circles that I needed. Using a pencil, I began transferring the lines on my pattern to the lighter of the two pieces of fabric. By folding the pattern along the lines I had marked on it, I was able to place the pattern on top of my fabric and trace a dashed line along its edge onto the fabric.
After I had transferred all the lines, I began sewing the two circles together. I stacked the two circles of fabric wrong sides together and stitched the smaller center circle, remembering to leave an opening for filling it. After I had added the filler to that section, I stitched the remainder of the seam closed and began stitching along the lines that radiated out from it. Being sure to backstitch the beginning and ending of each seam to lock the stitching in place, I began each seam at the center circle and stitched straight out to within two inches of the outside edge. Here I turned and began sewing parallel to the outside edge until I was within an inch and a half of where the next seam would go. This formed the outside sections and left an opening in each one for them to be filled.
Now that the sections were all sewn in, I could begin the process of filling them. I used a funnel (cut from the top of a two-liter soda bottle), and a plastic container to carefully add the filler to each section. I did not pack each section so full as to be tightly stuffed, but I did fill each one moderately full and pinned the openings closed. Though the lighting in this photo is a little odd, I chose it because it does show what the sections should look like. When I was happy with the level of the stuffing, I finished sewing up all the seams.
The next step was the drawstring. I simply made a long, thin tube from some fabric cut from my sheet and turned it so that the raw edge was on the inside. If you would like to skip this step on your own bag, simply use the cording of your choice. To make the casing for the drawstring, I first had to make an opening for the string to pass through. Working with just the outside layer of my bag, I made a cut from the outside edge straight down toward the existing seam. I stopped just short of the seam and then, turning the raw edges under, I stitched them in place so that they would not unravel. This made a V-shaped opening in the outside layer of fabric. To complete the casing, I folded the edge of the inside fabric down over the outside fabric and stitched it in place. Then I threaded the drawstring through.
Now that the basic bag was completed, the last thing to do was to make a “lid” for it. This was very simple. I just had to cut out, sew together, and stuff two more circles that were a little larger than the circle in the bottom of my bag. Using the measurement for the bottom circle, I added an additional inch and a half to all sides and cut it out. Putting right sides together, I stitched them together, leaving an opening so that I could turn it right-side-out. After it was filled, I sewed the final opening together and my bag was complete. Now all I had to do was to test it.
I had a package of fifteen bean soup on the shelf, so it became my test project. It called for letting the beans simmer for two and a half to three hours, so it was an excellent one to test! The standard “recipe” for things with a long cooking time seems to be to bring the food to a boil and let it boil for twenty minutes. Then it is transferred into the bag where it stays covered for twice the amount of simmer time normally called for on the package. I let the beans soak overnight, and after pouring off that water, I added my ham, the ham stock, and all the other ingredients I wanted it to have, even the ones that the package recommended putting in toward the end of the cooking time. I made sure there was not a lot of air space left at the top of my pot, since this reduces the effectiveness of the bag. I brought the soup to a boil, and leaving the lid on, I let it boil at a good clip for twenty minutes. Then I immediately transferred it into my bag, put the bag “lid” on, and cinched the bag closed. I felt around for hot spots and adjusted the stuffing to fill in anywhere I could feel heat escaping. Then I left it on the counter (never leave it on a surface that is a good conductor of heat) and waited for five hours.
Finally, the five hours were up! With anxious fingers, I loosened the drawstring, and removed the cloth lid. I lifted the silver lid of the pot and the steamy aroma of the beans rose to meet me. I fished out some of the beans with a spoon and tasted them. They were wonderful! They were completely done and tasted great! Now I only had one problem. I had put the beans into the pot at about nine o’clock in the morning thinking that I wanted to have extra time to let them finish if need be, since the cooking times for the bag vary somewhat depending on what you want to cook. Now I had another three and a half hours until dinner time, and the beans were ready to go. I decided to close the bag back up and see what would happen.
At dinner time, I opened the bag up and without reheating it, I served the soup—over eight hours after the last heat had been applied to them. They were excellent! This was fix-it-and-forget-it at its absolute best. The bag had allowed me to put twenty minutes of electricity into something that normally took two to two and a half hours and kept it hot without scorching or burning for over eight hours! It was amazing!
This project really highlighted the issue of faith for me. I had invested hours of my time into gathering materials, designing a pattern, and putting the whole thing together—all because some individuals on the Internet said that I could save energy and money using a heat retention oven. Even after I had made the bag I had to continue trusting their witness and could not even peek to see how the food was getting along, or I would have allowed the heat to escape and the experiment would have failed! To be so close and yet still not know if the project was a success or not was hard! How wonderful to know that my faith in Christ is not like an Internet project, subject to human error and faulty equipment! It is a sure expectation that the God who promised me an inheritance in His family can and will one day fulfill His promise. I need only take Him at His word. I was reminded of the verses in Hebrews where Christians are encouraged to be “…followers of them who through faith and patience inherit the promises…” for “…without faith it is impossible to please him [God]: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him” (Hebrews 6:12 and 11:6). I had gone through all the work and effort to make this oven based solely on the testimony of others, even though it may all have been a hoax, or their instructions may have been faulty. How much stronger then, should my faith be in the sure promises of a perfect God Who cannot lie! Have faith, fellow believers, for through faith and patience we shall inherit the promises!
December 6, 2012 update- I had been using this bag for several months to make sure that it worked well before I posted it to my blog site. However, I just discovered another advantage to the bag-style over the box-style heat retention oven. I used my bag the other day with soup that I was taking to a function at another location. My husband drove and I held the bag with it’s enclosed pot on my lap. I spent my time trying to compensate for the hills, curves, and stops to keep the liquid in the pot, which I could not see, level. I was pretty sure there was no way I would be able to arrive at my destination without having a fairly good-sized mess inside the bag, and thought that I would soon be testing to see how well it would clean up. (I was going to try hand washing it and let it air-dry.) Upon arrival however, I was surprised to see that there was no mess in the bag at all! Nothing– not even a line to show where the rim of the pot had been! The only explanation that I could come up with is that the drawstring design of the bag puts pressure on the lid and helps it stay sealed; a feature which the box-style oven does not have. 🙂
Dec. 2014 – If you liked this posting, take a look at my latest thermal cooking bag that is smaller and allows for the pot to have a handle. Great for households with one to two people!