Where do you even start? You start with tissue sample of a mushroom or what is called ‘spawn’. Spawn is not actual ‘spawn’ – it is the mycelium(root structure of fungi) set to a medium for later inoculation.
Growers do not use spores – spores are not genetically the same as the parent and can give a multitude of differences which can cause problems in production down the line.
Spawn is obtained a few ways and can be made by the grower or purchased.
Science of farming mushrooms. This is where mushroom farming meets laboratory in the process of mushroom farming. In the case of most mushrooms – a sterile media is preferred. Sterile of course is this word that most are unfamiliar and the complications of sterilization and techniques involved in keeping it sterile.
I grow Shiitakes and due to their slow growth rate the media I grow on has to be sterilized for best results and so the shiitake spawn has the best chance of surviving without competitor fungi like mold. Therefore a lab with laminar flow hood is required to keep bags sterile. Most farms growing mushrooms have a ‘lab’ of which can perform sterile work in various forms. Agar plates, liquid cultures, sterile media transfers and so forth have to undergo sterile ‘technique’ so that we do not contaminate our medias which can lead to big problems later.
In my lab I am capable of tissue cloning, spore capture, liquid culture, agar plates, media transfers, spawn bags, and production bags. It’s takes years to master sterile methods so that all movements and practices are second nature – to this day it is a continually learned and honed skill I will always work on.
Specialized bags are used in mushroom production that are equipped with filter patches which allow the medium to ‘breathe’ during incubation.
Mushrooms exhale carbon dioxide like we do and need to breathe in fresh air like us. During their incubation period mycelium can actually tolerate high levels of CO2 but require respiration so as to not promote bacteria who can tolerate no oxygen. The filters allow for gas exchange but now allow contaminants in during incubation – they are sealed using a poly bag sealer in front of the flow hood.
The mycelium will grow through the media in these bags for up to 8 weeks(shiitake) and then be taken out of the bag for ‘fruiting’ which is the mushroom formation.
Production and efficiency. We call these ‘blocks’ because of their generic look before and after harvesting – you can actually build with them too. Depending on the grower and their medium you get what is called ‘biological efficiency’ of which the mushroom is turning material into mushrooms for sale. In my case most of my blocks dry weigh 50oz(w/spawn) and recently set a record harvest of 2lbs 4oz from one block(36oz) so by dividing fresh weight of mushrooms 36 into the dry weight with spawn 50 we get .72% Otherwise translating into 72% biological efficiency. Which is impressive because most food industries don’t have this luxury of being able to calculate how efficient they will be whereas mushroom production can be calculated.
What is the block made of? Big question – predominately hardwood pulp because Shiitake and most of the mushrooms you see in production are ‘white rot’ fungus and eat hardwood materials that they can break down into their simple forms to be used again. Each grower has a unique medium to them but most blocks contain over 75% hardwood pulp with additions that will help the fungi grow and be prolific for harvest.