The production of high-quality freeze-dried strawheny pieces was studied by the
response surface method (quadratic model). Working pressure (P) and heating
plate temperature (T) were determined as the most important factors affecting
the criteria of final product quality (appearance/shape, colour; texture,
rehydration ratio). Freeze-drying experiments involving a thick layer of
strawbeny pieces were conducted in different operating conditions according to
a two-factor (F: T) experimental design. The su$ace response method allowed
us to graphically determine optimal working conditions. By superimposing all
quality criteria contour plots, the optimal conditions found were P = 30 Pa and
T = 50°C. The freeze-drying time ranged fi-om 60 to 65 h. The experimental
values for freeze-drying time, appearance and colour of freeze-dried strawberries
obtained with these optimal conditions were very similar to those predicted tly
the second-order su$ace response model.