Solar Cooking Archive Discussion Forums

coconino · Joined: 21 Nov 2006 Posts: 77 Location: Sunny Brixton

After yesterday's successful outing with the Heaven's Flame, and with the weather looking good, I decided it was time to take my Parvati cooker for a test drive. I made the cooker a couple of weeks ago, following Mrs. Shobha Pardeshi's excellent and clear instructions, but haven't had the opportunity to use it until today.

The test used a blackened two-part tiffin tin with three eggs placed without water in the base part and half a cup of rice with one cup of water in the top part. The temperature probe was inserted through a hole in the centre of the top lid and passed out through the opening of the enclosing bag.

As can be seen from the graph, boiling point was reached rapidly compared with yesterday's Heaven's Flame test, in around 90 minutes as opposed to four hours for the Heaven's Flame, and with almost identical weather conditions and ambient temperature. The first reading was a couple of minutes after it was rigged, which accounts for the 25C start temperature. The meter reading reached 101.8C one hour and 40 minutes into the test and hovered above 101C until the test concluded.

Once the test started, it was immediately apparent that the cooker worked very well, and even by putting a hand into the empty cooker its power could be felt. I was very impressed and surprised that it worked so well on an early April day. When two hours had passed I felt confident that the contents would be cooked and when the container was opened I found that both the rice and eggs were very nicely done. As soon as he had seen the results my son declared that he wanted a Parvati cooker for himself!

The set-up with thermocouple probe in place. Note the stand made from wire.

Thermometer showing 101C after 90 minutes.

Cooked rice and eggs after two hours and ten minutes. The small hole in the lid (beside the cracked egg) is to allow the thermocouple to be inserted.

A view of the cooker without stand or container.

Another view of the cooker, showing tabs added for anchoring cooker against breeze.

Close-up of tabs.

Parvati cooker during construction. Note the tabs which are not in the original design. After this stage the cooker was covered in several layers of newspaper stuck using flour paste and left to dry before being painted. The silver lining was added last.

Brit from Norway · Joined: 27 Dec 2006 Posts: 17 Location: Norway

I really hope that a lot of people will see this impressive test! The diagram with the temperature readings and all the photoes are very convincing!
Regards Brit
_________________
Best wishes to you all! Keep up the good work!

coconino · Joined: 21 Nov 2006 Posts: 77 Location: Sunny Brixton

Well, if I had any doubts about solar cooking here those doubts are gone now after the weekend's results. The next thing is to get hold of some recipes which suit this kind of cooking. I've been looking through the recipe section for ideas and I'll try your idea of rice pudding. I'm keen try vegetables in a soup or stew but things like bread will have to wait until the full summer arrives. What sorts of things have you done in your Parvati?

Brit from Norway · Joined: 27 Dec 2006 Posts: 17 Location: Norway

Hello!
I have made various kinds of food
1. Chicken, one chichen with salt and spice and chopped onion. No water added. Other fowls go equally well.
2. Fish, add spice but no water. Salt when served.
3. Casserole : Minced meat, oil, tomatoes, chopped onions, spice, rice, add water twice as much as rice. Enough to serve three persons who are not too hungry.
4. Bread, one small loaf made out of 2.5dl water or milk, 6,2 dl flour, 0.5 teaspoon salt and yeast to match the amount of other ingredients. Two hours in the cooker resulted in thin soft light brown crust and the loaf was baked through to the middle. Turn 180 degrees after 1 hour.
5. Potatoes, add no water. Whole potatoes take rather long to be baked through.
6. All kinds of vegetables, add no water (but cabbage does not smell good when cooked alone. In a soup it is all right)
I think many different casseroles will be good in the cooker.
I have not tried beans or peas yet. They will need to be presoaked, and will propably need more than two hours. Maybe three?
If you want to make soup, it will be better to bring the water to the boil first, and then add the other ingredients.
Good luck!
Regards
Brit
_________________
Best wishes to you all! Keep up the good work!

coconino · Joined: 21 Nov 2006 Posts: 77 Location: Sunny Brixton

A second test today was slower than Monday's test but still produced good results in the end. Although the day was bright, the sky was more white than blue and the sun was slightly diffused, casting soft-edged shadows. No pictures this time as I forgot to pack my camera.

Following a friend's suggestion, I tried cooking Esau's "mess of pottage" in the top container of the tiffin tin, but although the result was tasty I doubt whether Esau would have exchanged his birthright for what I produced.

In the bottom, following my son's suggestion, I tried popcorn. This did not work at all, though I am not yet dissuaded that it might be possible with the right technique.

Mess of pottage
Strictly speaking, the onions should be fried and caramelised, but I simply combined all the raw ingredients in the container and set it to cook. I also forgot to bring olive oil, so that was missing too. The result tasted good but I know it can be improved.
100 g (1/2 cup) green lentils
60 g (1/4 cup) brown rice
370 ml (1 1/2) cups water
1/2 medium onion, chopped
salt and lemon juice

This is an almost identical curve to Monday's test except that this is stretched over four hours instead of two. My subjective assessment is that the slowness is due to it being a slightly hazy sun and there being a greater load to cook than in the earlier test, by about half. I made a note of an improvement in the sunshine at around 11:30 and again at around 13:00 and these observations can be seen reflected in the graph.

I may do another test tomorrow with an increased load to assess whether that is as much of a factor as it seems.

coconino · Joined: 21 Nov 2006 Posts: 77 Location: Sunny Brixton

Brit from Norway · Joined: 27 Dec 2006 Posts: 17 Location: Norway

You have a point there.
It will of course depend on the family's eating habits in summer.
In our area most families have one hot meal every day in the summer as well as the rest of the year. But when the weather is warm, many families prefer to cook outside, they don't want to make extra heat in the house. The outside cooking is of course done on charcoal, adding to the CO2 emission.
I think that it would be good for us all, if most of the outside cooking could be done by solar heat instead. However, we have a long way to go!
Another thought: most people drink coffee and tea year round. That is another use for the solar cooker.
Some cookers, like the Parvati and the parabolics, may be used in spring and atumn too.
Regards
Brit
_________________
Best wishes to you all! Keep up the good work!

Brit from Norway · Joined: 27 Dec 2006 Posts: 17 Location: Norway

I was thinking about soup with vegetables.
This is really about keeping the vitamin C level in the vegetables as high as possible.
Water takes a long time to heat. A slow heating prosess will destroy more of the vitamin C in vegetables (and also in fruit and berries). Temperatures between 15 and 50 degrees Celcius are worst.
When the water is boiling when the vegetables are added, the soup will get quickly past the critical temperature range, and more of the vitamines will keep.
With other kinds of soup I don't think it matters much.

Regards
Brit
_________________
Best wishes to you all! Keep up the good work!

coconino · Joined: 21 Nov 2006 Posts: 77 Location: Sunny Brixton

coconino · Joined: 21 Nov 2006 Posts: 77 Location: Sunny Brixton

Brit from Norway · Joined: 27 Dec 2006 Posts: 17 Location: Norway

My thoughts about this issue came from what I learnt in my year at housekeeping school back in 1966. I understand that certain enzymes in vegetables and fruit will speed the decomposition prosess at rather low temperatures. These enzymes are quickly destroyed at boiling temperatures (and a little lower). Hence blanching of vegetables before freezing.
It will be quite another matter with pills of vitamin C - no enzymes.
I found a - rather long - article about vitamin C in fruit and vegetables here:
http://rics.ucdavis.edu/postharvest2/pubs/science1.pdf
It seems that my old teachers were rather up to date.

You are quite right about the leaching though. As little water as possible if you are not making soup or using the cooking water in a sauce.
(They taught us that too)

Regards
Brit
_________________
Best wishes to you all! Keep up the good work!

coconino · Joined: 21 Nov 2006 Posts: 77 Location: Sunny Brixton