Feeding Hamsters Grapes and raisins

Grapes and raisins are one and the same fruit, raisins are just simply dried grapes. Raisins are rich in nutrition and extremely high in calories, they are a good source of iron and potassium, and contain a large amount of vitamin A and some vitamin B. Sulfur dioxide is used in the drying process of most dried fruits, it is a colorless toxic gas, and is also used as a preservative in alcoholic drinks. Unless you have a hamster that regularly hit's the bottle you shouldn't have a problem with that. Sulfur dioxide is also used in the drying process of fruits, apricots, sultanas, raisins and many other fruits but the drying process destroys most of the Vitamin C in the fruit, this preservative is used to maintain the appearance of the fruit rather than to prevent it from decaying.
Raisins also have a very high natural sugar content which is 60% by weight, this is fructose.

Grapes and raisins are generally not considered to be toxic to hamsters, but here are a few points to bear in mind before feeding these to any of your pets. Grape and raisin toxicity in dogs is already well documented, and is still relatively new ground, the consumption of grapes and raisins are known to present a potential health threat to dogs. The toxicity of these fruits in dogs can cause the animal to develop acute renal failure. No one knows for sure yet why these fruits are toxic to dogs, and if only certain breeds of dogs may be affected. It is still not known for sure if theses fruits pose a potential health hazard only to dogs or if other animals may be affected by them.
Grapes in their fresh or dry form are known to cause the animal to develop acute renal failure (Kidney failure) This is a problem that affects the kidneys ability to function adequately. It can be Acute which is a sudden appearance, or chronic, meaning the symptoms can appear over a period of time.

Most animal centers are now advising that grapes and raisins should not be fed to any animal until the toxic substance has been identified.

Mycotoxins are thought to be involved. Mycotoxins are toxic compounds produced by fungi that contaminate plants, mycotoxins are not destroyed by cooking, freezing, or drying.