Abstract
This research work was focused on evaluating the vacuum freezing (VF) of coffee extract under different process conditions as well as on its comparison with air freezing (AF) and contact freezing (CF). Regarding VF, extract concentration (10 to 40 oBrix) did not affect freezing time (for sufficiently high pressure drop rates), whereas extract layer thickness had significant impact, with 50% higher process times for samples arranged in 6-mm-thick layers in comparison with 4-mm-thick arrangements. Moreover, reduction of pressure drop rate (from 0.57 to 0.37 kPa s−1) caused an increase of up to 5 times of VF time. In comparison with AF and CF, VF led to significantly smaller freezing times along with higher mass losses (of 26–43% contrasting with 1–2% losses for AF and CF). This fact, allied to the extremely porous structure formed during VF, makes this method particularly interesting for soluble coffee production by freeze drying.
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