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For quality of protein, and preservation of nutrients, low-temperature cooking is by far the best method.
Heat alters food components. Heat is the speed of movement of molecules ~ the faster the molecules move around, the hotter the substance is. If the molecules of food, which are very large and complex molecules, move more rapidly than when the animal or plant was alive, they can break apart. The higher the heat, the more it causes the delicate molecules to break apart, causing the destruction of nutrients in the food.
With solar cooking, the molecules of protein and other nutrients are spared the ultra-high heats found in electric and gas ovens. Solar cooked foods in general have far more quality protein, vitamins, enzymes, and other fragile nutrients than high-heat-cooked foods.
So, what cooking temperatures are safe?
Please see the Solar Cooking Archive for a concise explanation.
Here's a recap:
The danger zone is 50 to 120 degrees Fahrenheit. Germs that are dangerous to humans grow at the temperature of the human body, around 100 degrees F. Food should be kept below 50 or above 120 most of the time. Basically, if your solar oven gets 180 degrees or higher, and the food, including meat, is kept in it for several hours, it will be safely cooked. And, it's alright to put the food in the SO when cold, even frozen, as long as the SO heats up at a normal rate. If the SO stays at around 100 degrees for several hours with uncooked animal-source food in it, that food should not be trusted.
The one big caution is ground meat of all types. Germs grow only on the surface areas of meat, not inside the flesh. Since ground meat has such a huge proportion of surface area, germs grow profusely through it. It is very important to be sure to cook ground meat thoroughly, keeping it at 180 degrees or higher for several hours, or if this is not possible, then get a meat thermometer and make sure the internal temperature of the
described slow-cooking of meats back in the 1960's.
"Proteins are not harmed when meats are cooked at low temperatures; at high temperatures, some of the essential amino acids are broken apart by heat, and their health-promoting value is decreased."
"...the B vitamins are not harmed even by long cooking at low temperature except at the surface of the meat. Above the boiling point [212 degrees F], the destruction of several B vitamins increases in proportion to the temperature."
"All the B vitamins and the minerals supplied by meat, iron, copper, and phosphorus, dissolve in water and can be lost if meats are soaked or boiled and the cooking water is not used. Juices which seep from frozen meats during thawing and those which are lost in the ... pan should be used in gravy or added to soup stock."
"You can increase the nutritive value of meats containing bone by soaking or cooking them with a little acid, as tomatoes, vinegar, or sour cream. The acid dissolves some of the calcium from the bones into the gravy or sauce."
"The high temperatures used when meats are fried, boiled, or cooked in a pressure cooker are particularly destructive to the health-promoting value of the protein."
"In experiments were identical roasts were cooked at different oven temperatures to the same degree of doneness, roasts cooked for 20 to 24 hours were preferred in 100 percent of the taste tests to roasts cooked in 3 hours or less. Although the cooking time seems startling at first, the meat is so amazingly delicious, juicy and tender, slices so beautifully, and shrinks so little that meats cooked at higher temperatures no longer taste good to you." [Don't we know it!]
Adelle sounds positively prophetic in her description of "Slow Roasting" of meats (more on this in the Solar Recipes section):
"In slow roasting, the oven temperature is set approximately at the temperature you want the meat when it is done. Just as meat taken from a refrigerator will warm to room temperature, so will meat put into such an oven heat to oven temperature. It cannot burn; it needs no watching; vitamins and proteins cannot be harmed at such low heat; almost no fuel is needed to cook it. One might say that it cooks itself. Many warming ovens are adjusted so that a pilot light maintains a constant temperature of 165 degrees F., ideal for this type of roasting."
She couldn't have described solar cooking any better if she'd been on that subject. This was written in 1947! Source: Let's Cook It Right by Adelle Davis.
Solar Cooker Caution #1:
There are some vitamins and food components that are destroyed by light, even by relatively short exposure of half an hour or so. If you're eating many meals from a solar cooker, our suggestion is to use light-tight cookware such as metal pans with metal lids, or pottery ware with metal or pottery lids or covered with foil. If you wish to cook in glass, you should wrap your glass pans with aluminum foil or some other light-proof material (black cloth?) while in the cooker. This goes for amber or other tinted glass as well. Over the many hours that food is in the solar oven, much light penetrates all glass, tinted or not. Only opaque cookware will block the light from affecting the specific nutrients in the food.
Light can destroy certain vitamins and nutrients!
Solar Cooker Caution #2:
Enzymes are living chemicals that are catalysts for biological, chemical reactions. They are present throughout all living tissues, plant and animal. Enzymes in foods will continue causing chemical changes in the food, including destroying several vitamins and other nutrients. This is a main reason why fresher food is more wholesome.
Enzymes destroy nutrients. Bring your foods up to full solar-oven temperature as quickly as possible to destroy the enzymes.
To prevent destruction by enzymes, one should get the solar oven to full temperature before putting the food into it.
Enzymes are proteins, and as such, are destroyed by heat above a certain temperature. This is one of the reasons why canned food will not go bad. The canning kills germs in the food, of course, but it also destroys the enzymes in the food, so that they cannot continue to act on the other chemicals in the food. To prevent as much enzyme action as possible, nutritionists recommend that when steaming vegetables or other foods, one should get the steaming water boiling first, then add the vegetables to the pan, instead of putting the vegetables into a pan with cold water. The hot water quickly destroys the enzymes, stopping them from altering the food. Putting food into a steamer with cold water allows the food to warm up more slowly, which allows enzymes to act for longer periods of time, destroying more nutrients.
The warmer the temperature, the faster the enzymes act to alter other chemicals in a food, up until the point at which the enzymes are destroyed by heat. As your food warms up in the solar oven, the enzymes will be getting gradually warmer, and will be altering the vitamins and nutrients in the food over a longer period of time than if you had pre-boiled the food on a gas range.
However, at near boiling point, enzymes are destroyed. So it is wise to make sure your solar oven is already as hot as it will get or at least to boiling point (212 degrees F, or 100 deg. C) before putting the food into it. When possible, use other means of getting the food to near boiling point quickly, such as pre-steaming or pre-boiling or pre-roasting for a short time before putting it into the solar oven. Alternatively, one can prepare the food in such a way that it is in small pieces, or is in a shallow pan, both of which will heat up more quickly than large pieces or food in a deep pan. And in the solar oven, the small pieces of food will not dry out, but stay wonderfully moist.
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SO: Solar Oven, a contraption that, darn it!, cooks using only sunlight
SQ: Solar Barbecue, a solar oven made by converting a standard barbecue