Dear all, we need a procedure to rapid drying plant materials from field or greenhouse experiments to rapidly denaturing enzymes, kills micro-organism and stabilizes the tissues. On one hand we want harvest hundreds of plants and cut it immediately into several parts (leaves, stems, ears and so on) in a short time to avoid changes in daily sequence of metabolic processes. Drying over days in compartment dryer at 105°C or airing cabinet at 60-75 °C for 24 or more hours is not possible because we would need too much for 100 or more plant sample daily. On the other we want determine the dry matter and analyze the content of nitrogen, carbohydrates and other compounds in it after drying without losses. Which power rating (watts) can you recommend, which sample size, when a constant weight will be achieved: 5 minutes, 10 minutes or how many? Have published your experiences with simple domestic microwave ovens anywhere? Commercially microwave ovens are to expansive for us in the moment. Thanks for your answers, regards Petra
Microwaves are initially not drying a sample, but heating the water within the sample. This is cooking your sample while it gets finally dry or even burnt. If the samples are tea leaves, then the tea may taste quite differently than usual.
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Dear Petra Seidel,
I have some small experiences of using microwave oven (frequency of 2450 MHz) for making dried leaves to share with you. From the results, I found that the microwave power of 900 W worked pretty well with my sample. I used to perform lower than 900 W and I found that my sample provided brown color. So, you may try with this condition (900W). The sample size should not over the microwave tray. The thickness or the layer of your sample should be appropriate because microwave have the limitation of penetration depth. For the drying time, you need to try by yourself because it depends on the nature of sample (especially initial moisture content). Hopefully, I will useful for you.
Sincerely,
Thank you, Reto Jörg Strasser, for pointing out that the taste of tea leaves can change after drying in the microwave.
What usually happens when drying? There is a dehydration due to evaporation. This evaporation can accelerated by higher temperatures. Usually, in order to prepare plant material for analysis it is dried at 105°C in compartment dryer to constant weight. If the weight remains constant the sample is completely dried. This takes several hours. Several hours with 105°C. 105°C is a temperature at which water should boil- or? In the microwave this drying process takes a few minutes. You can buy microwave for drying of samples from a laboratory supplies dealer. They are very expensive: 7000-8000 €. Domestic microwave ovens are much cheaper. Recently I read a publication reported about drying of parts of cereal plants in domestic microwave ovens to prepare for further analysis. That’s why I asked if anyone has experience with this obviously usual procedure.
Thank you, Traiphop Phahom, for sharing your helpful experiences with microwave drying of plant materials! You are right, for drying time I have to try it by myself. Maybe someone else who has experience with cereals will answer...Best regards, Petra
Drying means loosing water. This can be stimulated by increasing the ambient temperature or by decreasing the ambient air pressure. Combining both (often done in a desiccator linked to a vacuum pump, accelerates the drying (equal water loosing) process in a subtle way. Ice Cristal formation has to be avoided by keeping the vacuum and temperature in a physiological range, but stimulating the evaporation of water (like swedding). Keeping the pressure as vacuum and the ambient defined louvered temperature constant under control, keeps your e.g. leaf samples green and dry (even then if you don't use the dry stuff as GREEN THEA). The leaves have to "feel" like we do in a healthy and enjoyable SAUNA. Plant material for research has to feel happy as well. Good luck. Reto J. Strasser Switzerland
Drying is one of the most expensive unit processes. There are hundreds of different methods of drying, but none is all purpose ones. Regards,
Thanks, Reto, that make sense. But I don’t think that with this method you can dry hundreds of samples, such as those that doing occur during a harvest, on one, namely on harvest day.
Yes, I know, Miroslaw and thank you for your answer. But I asked if anyone ghs experience with drying in household microwave oven. Regrads, Petra
microwave is a good but critical technique
any way drying in microwave depends on watt
i.e, 400w need long time than 800 w exposure
also, type of sample
leaves need long time than roots
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