[Nhcoll-l] Freeze-drying of mushrooms

[Simon Moore]

Hi Alejandra,

I have had fairly considerable experience in freeze-drying mushrooms for the museums in Hampshire.  I was using an old-fashioned Edwards EF2 machine and putting in the specimens at -20 deg C, having weighed them initially and recorded the weights in a log book.  The specimens were then freeze-dried for about 5 days, removed from the machine and weighed again to monitor the loss, then. Returned to the machine for a further 2 days and re-weighed. The process continued usually over a period of about 10 days to 2 weeks, until the specimens weighed the same as the previous time - achieved a constant weight, so they were removed for storage. The vacuum was around 0.1 Torr which equates to 0.13 mbar. If your machine doesn’t go below 0.4 mbar then the process will take a bit longer so be patient.

For coloured specimens, the initial colour, before treatment, was recorded on the specimen label using watercolour or gouache paint.  Specimens were stored in grip-top polythene bags in cupboards and the room RH was maintained at between 40 to 50%.  This reduced fading and some pigments are very photo-labile such as the red colour in fly agarics. 

This method had 100% success rate. 

With all good wishes, Simon 

Simon Moore MIScT, RSci, FLS, ACR
Conservator of Natural Sciences and Cutlery Historian.

www.natural-history-conservation.com


> On 28 Nov 2025, at 08:55, Alejandra <encinaruda at gmail.com> wrote:
> 
> Dear friends,
> 
> First time here, thanks for accepting me!
> 
> I am biologist working for a village in Andalucía (Spain) where they want to create a mycological museum. I've been collecting mushrooms for a month and freezing them (in a normal freezer). Then, I've made six attemps to freeze-dry some specimens -using a freeze-dryer (photo attached)- but somehow I don't success yet. I couldn't find any protocol for freeze-drying fungi online, and was wondering if here anyone has worked with it o anything similar. 
> 
> I have doubts regarding freeze-drying in itself but also the preservion of the specimens afterwards. So, these are the parameters and times I've been trying and some of my doubts:
> 
> - I freeze the mushrooms for about 4-6h at -50ºC, and then I've been trying different sublimation times (I aim to achieve 0.1mbar but the machine doesn't go below 0.4mbar): I tried half a dar, one day, two days, three days... For small mushrooms such as Marasmius or Tricholoma, three days seem enough. For bigger mushrooms such as Lactarius or Lepista, I think at least four. For somehting like a big Boletus I don't even know. Any suggestions?
> 
> - I've been doing two things which I don't know if they are counterproductive. I've made small holes in the widests parts of the mushrooms with a needle, hoping that by doing them mushrooms will freeze better and freeze-dry faster. Moreover, I've been doing cycles of freezing-sublimating, i.e. freeze 5h, sublimate 24h, freeze other 3h, sublimate 24h.... Maybe braaking the vacuum and creating water crystals again is not intelligent... Any idea if this makes sense?
> 
> - The freeze-dryer has the option of applying heat. Would be a good idea to apply some heat after the sublimation so as to make sure all humidity goes away? How much and for how long?
> 
> - Okay, now with the "aftercare". The only time I achieved positive results (mushrooms were beautiful and dry), I took the mushrooms home without much protection and put them inside a plastic box and closed it. A few days later I opened it and found them to be soft and damaged by moisture. Next time after taking them out of the freeze-dryer I will inmediately put them on the box but filled with silica gel. Then, when remaining humidity is absorbed, I would like to cover the mushrooms with some kind of barnish. I have an acrylical spray one, but was also wondering other options (that do not change too much the color or texture, that preserves the specimens agains humidity and insects, and that make them a bit resistant and tougher). Any opinions about any of this?
> 
> Thank you a lot for taking the time to read and consider my situation :) Any suggestion or resource is deeply welcomed. 
> 
> Wish you a good day,
> 
> Alejandra
> 
> <IMG_5507.jpg>
> 
> 
> <FA86D3C6-A7D8-49AF-82C7-C7DA95534B0D.JPG>
> 
> 
> 
> _______________________________________________
> Nhcoll-l mailing list
> Nhcoll-l at mailman.yale.edu
> https://mailman.yale.edu/mailman/listinfo/nhcoll-l
> 
> _______________________________________________
> NHCOLL-L is brought to you by the Society for the Preservation of
> Natural History Collections (SPNHC), an international society whose
> mission is to improve the preservation, conservation and management of
> natural history collections to ensure their continuing value to
> society. See http://www.spnhc.org for membership information.
> Advertising on NH-COLL-L is inappropriate.