Machine dehydrating (also known as food dehydration) is a process of removing most of the water content from food. This technique can extend the shelf life of food and reduce storage and transportation costs. Compared to fresh food, dehydrated food has the following main differences:

1. Water Content: Fresh foods contain a large amount of water, whereas dehydrated foods have had most of their water removed.

2. Weight and Volume: Due to the removal of water, dehydrated foods are lighter than an equivalent volume of fresh foods and take up less space.

3. Nutritional Composition: Some nutrients such as Vitamin C and certain B vitamins may be lost during the dehydration process. However, minerals are typically not affected. Proper dehydration temperatures and times can help maximize nutrient retention.

4. Texture and Consistency: Fresh foods are usually more tender, crisp, and juicy, while dehydrated foods tend to be drier and harder.

5. Shelf Life: Dehydrated foods generally have a much longer shelf life than fresh foods because the lack of moisture makes it difficult for microorganisms to grow.

6. Flavor: Although the dehydration process might affect the taste of the food, many people rehydrate dehydrated foods before eating or cooking, which can restore its original flavor and even better.

7. Usage: Dehydrated foods can be eaten directly or rehydrated before cooking. They are commonly used for outdoor activities like hiking and camping, or as emergency reserve food.

8. Storage Conditions: Dehydrated foods typically need to be stored in dry, cool places to maintain their best condition and prevent moisture absorption.

It's important to note that while food dehydration has many advantages, it cannot completely replace fresh foods. To ensure a balanced diet, it is recommended to consume both fresh foods and an appropriate proportion of processed foods.