Much of the lettuce we buy has likely spent time in a giant vacuum chamber. Commercial vacuum cooling of produce began in Salinas, California, in 1948 and is now commonly used for lettuce and leafy vegetables. Packed greens enter a sealed chamber where much of the air is removed. Lower pressure lets a tiny amount of water in the leaves evaporate, carrying heat away and rapidly cooling the greens. For every one percent weight lettuce loses as water, its temperature drops 10 degrees. Who would’ve thought store-bought lettuce has something in common with vacuums?
Growing Home: Storing Lettice in a Vacuum
