You can freeze dry rose petals by the process of sublimation. Sublimation involves freeze drying the petals for around 12 hours at a prescribed temperature. Moisture from the petals is gradually pulled out in vapor form by a vacuum pump. This vapor accumulates in one chamber of the pump. It turns to ice as it condenses in a different chamber. A vacuum freeze dryer fitted with adjustable temperature setting is ideal for freeze drying rose petals on a small scale.
- Collect the roses
Harvest fresh roses using pruning shears. Choose roses that have opened fully to ensure an easy removal of petals.
- Remove the petals
Cut the stems of the roses. Place them in a container filled with water for around 12 hours. Remove the petals from the roses, and throw away torn or damaged petals.
- Set the dryer's temperature
Set the freeze dryer’s temperature to minus 5 degrees Fahrenheit. Shut the dryer’s door. Seal the door by turning on the vacuum for approximately 10 seconds. Allow the dryer’s temperature to reach minus 5 degrees.
- Place the petals in the dryer
Place the rose petals on the freeze dryer’s tray. Shut the dryer’s door. Turn on the vacuum. Leave the petals in the dryer for 48 hours.
- Raise the dryer's temperature
Raise the dryer’s temperature to zero degrees Fahrenheit. Let the petals continue to dry at this temperature for an additional 48 hours.
- Increase the temperature
Increase the dryer’s temperature by an additional 5 degrees Fahrenheit. Continue to move up the temperature until it reaches 20 degrees Fahrenheit.
- Check the flower petals
Remove the petals from the dryer and touch them to check their temperature. If the petals are cold, place them back in the freezer and raise the temperature by 5 degrees Fahrenheit per day until they are not cold to the touch. When the petals have dried completely they will not be cold, as dried petals do not retain moisture.