Freeze drying

Application note: N°F015Why the need to measure the relative humidity?Advantages and inconvenientsNovember 2011Fresh raspberriesFrozen raspberriesFreeze dried raspberriesFreeze drying cyclePeople use freeze drying topreserve material, such aspharmaceuticals. Many pharmaceuticalswill degrade prettyquickly when exposed to waterand air, for the same basicreason that food degrades.Chemists can greatly extendpharmaceutical shelf life byfreeze-drying the material andstoring it in a container free ofoxygen and water. Similarly,research scientists may usefreeze drying to preserve biologicalsamples for longperiods of time. Freeze driedbiological samples are also bigin the florist world. The freezedrying process has also beenDuring the lyophilisation (freeze drying) process,the freezing is very important: rapid cooling resultsin small ice crystals, useful in preserving structuresto be examined microscopically, but resulting in aproduct that is more difficult to freeze dry. Slowercooling results in larger ice crystals and less restrictivechannels in the matrix during the dryingprocess.Environment temperatureProduct temperatureOptimising the processused to restore waterdamagedmaterials, such asrare and valuable manuscripts.Freeze dried material can bestored at warmer temperatureswithout suffering degradation.Freeze dried products can bestored without cryogenic orfreezing facilities, the energycost and the risk of productloss from power failure isgreatly reduced.As the product is dried outwithout excessive heating,proteins and other productsthat would be thermally denaturedcan be successfullypreserved without loss ofactivity.As products are much lighterwhen they are dry, freeze dryingoffers the benefit of reducingtransport costs.Compared to advantages, theonly disadvantage is thatfreeze drying is very a expensiveprocess in terms ofhigh investment and maintenancecosts and the productioncapacity is limited due tothe long process time.As freeze drying is an expensiveprocess, once the productis freeze dried, it is importantthat it is monitored during therest of the life span of theproduct.Air inlets: During the freezedrying process the air inletsmust be monitored. Thedryer the air entering theroom, the better.By their nature, freeze driedproducts are hygroscopicand exposed to water duringstorage can destabilise theproduct. This means that thefreeze dried products can“never” leave a controlledzone.The control of the storagearea where freeze driedproducts are placed is compulsory.The freeze drying processnever comes alone, once theproduct is dry, there is then aneed to pack the product:there are always filling machinesthat are placed in asterile areas or isolatorswhere humidity must be controlledand can be sterilizedwith hydrogen peroxide.Residual humidity in elastomericstoppers cancause degradation of freezedried products. Prior to packagingthe product, stoppersare typically washed, steamsterilised and dried. Thesteam sterilisation processdrives humidity into the stopper.If the drying conditionsfor the stopper are not optimised,residual humidity cantransfer into the freeze driedproduct over time.Packaging used for freezedried materials must be impermeableto relative humidity.

Application note: N°F015Contact us:November 2011Rotronic is represented in over 40 countries around the world. An up to date list of all our partners is available on our website:www.rotronic.comSWITZERLANDROTRONIC AGGrindelstrasse 6,CH-8303 BassersdorfPhone: +41 44 838 11 44Fax: +41 44 837 00 73www.rotronic.comFRANCEROTRONIC Sarl56, Bld. De Courcerin,F-77183 Croissy-Beaubourg.Phone: +33 1 60 95 07 10Fax: +33 1 60 17 12 56www.rotronic.frSINGAPOREROTRONIC South East Asia Pte Ltd16 Kallang Place #07-04Singapore 339156Phone: +65 6294 6065Fax: +65 6294 6096www.rotronic.com.sgGERMANYROTRONIC Messgeräte GmbHEinsteinstrasse 17-23DE-76275 EttlingenPhone: +49 7243 383 250Fax: +49 7243 383 260www.rotronic.deUKROTRONIC Instruments UK Ltd.Crompton Fields, Crompton WayCrawley, West Sussex, RH10 9EEPhone: +44 1293 57 10 00Fax: +44 1293 57 10 08www.rotronic.co.ukITALYROTRONIC Italia srlVia Repubblica di San Marino, 1I-20157 Milano (MI)Phone: +39 02 39 00 71 90Fax: +39 02 33 27 62 99www.rotronic.itUSAROTRONIC Instrument Corp.Suite 150, 135 Engineers Road, Hauppauge,NY 11788Phone: +1 631 427 38 98Fax: +1 631 427 39 02www.rotronic-usa.comCHINAROTRONIC Shanghai Rep. Office2B, Zao Fong Universe Building, No. 1800ZhingShan West Road, Shanghai 200233ChinaPhone: +86 21 644 03 55Fax: +86 21 644 03 77www.rotronic.cn