Freeze-drying food involves extracting water from food, not conventional freezing. Removing the water from food keeps it from spoiling for a long time and reduces the total weight of the food. This is why freeze-dried food is preferred by hikers, astronauts and others who need to carry food but don't want to carry a lot of weight.
Wash your strawberries by rinsing them in cool water and then drying them thoroughly on a clean kitchen towel.
Remove the stems and slice the berries thinly.
Place the sliced berries separately on a paper plate and then place them in a zip-style freezer bag. Press the air out of the bag without squishing the berries and seal the bag.
Put a layer of dry ice on the bottom of your cooler or five-gallon bucket. Always wear gloves when handling dry ice.
Place the bags with the berries on top of the dry ice. Stack the bags on top of each other if you have to.
Replace the lid on the cooler or bucket, but don't seal it tightly. Some air needs to escape while the dry ice is evaporating.
Seal the lid completely once the dry ice has evaporated. You can now keep the berries in the cooler or bucket with the lid sealed tight, or store it in a cool, dry place.
Always wear gloves when handling dry ice. Prolonged exposure to dry ice will freeze cells and cause injuries similar to a burn.