How high potassium foods are prepared is important in determining how much potassium in the food will get into your body. It is no good to have 4700 mg of potassium in the food you would consume and then lose a large amount of it during the preparation.
Most methods of cooking make it easy to keep the potassium in the food. But one method in particular frequently pulls potassium out of the food.
The easiest method to keep all the potassium in the food is to eat the food raw. That is a good method for most vegetables, fruits and spices. It is not recommended for animal products though. Animal products are more easily contaminated and can more easily grow harmful organisms, although plants can also be contaminated.
If the plant foods are picked fresh, consumed fresh and washed prior to eating, they have a low likelihood of having harmful organisms. If you know the producer of the plant food, you can determine the possibility of chemical contamination. If you know what to look for you can determine if the fruit or vegetable is spoiled.
For most animal products though, it is difficult to spot contamination. Even the most careful farmer can have meat, dairy or eggs with harmful organisms. Almost all eggs have salmonella on the shell surface. All poultry should be assumed to have salmonella on the surface. Meats can have organisms hidden and will not show the problem like spotted or softened produce does. Dairy can have microorganisms that don't show if not pasteurized.
When handling animal products, the utensils used with the raw product should not be used with the cooked product unless thoroughly washed before using with the cooked product. Hands, dishes and utensils should be washed before touching the cooked product if they had contacted the raw previously.
Although there are knowledgeable producers and consumers that have used raw animal products safely, I feel it is too difficult. Some of my friends and I have had contaminated raw animal products from sources we trusted. So I feel all meat and egg products should be cooked, and dairy pasteurized.
For high potassium foods, you have a multitude of choices for preparation. You can eat it raw after washing. You can steam it, bake it (without baking soda or powder), fry it, grill it, roast it or broil it. These methods will lose none or minimal amounts of potassium, and can be used with most dishes. Many barbeque enthusiasts already have tried various vegetables grilled. To mention just a few, peppers, potatoes, onions, and zucchini are great sliced and grilled.
Boiling in water is the main preparation method that will lose potassium from many foods. It pulls the potassium into the water. If the water is consumed though, you will consume all of the potassium. This is commonly done with soups, chilies and stews. If the water is discarded, it will reduce the amount of potassium you get from the food. Combine that with the common method of adding salt to the water the food is boiled in, and you will have also increased the sodium, thus ruining the potassium to sodium ratio, and reversing the healthful effects you are looking for.
A good method for preparing intact grains, such as rolled oats or quinoa, is to add just enough water to soak into the grain and then microwave the dish. This will heat the grain and destroy any organisms and make the grain soft enough to eat. All the water is driven into the grain and is consumed so no potassium is lost. This can also be done with dry lentils and beans, although the soak time is longer.
Of course, spices can be added at any time and will increase the potassium content of the dish while adding flavor.