When we talk about mushroom bags, we’re generally talking about autoclavable, polypropylene, bottom gusseted filter bags. These bags come in all shapes and sizes. In this video we’re going to look at the three most common (and quite possibly only) filtered gusseted bags on the market. The grow bags purpose is to contain your substrate or spawn in a sterile, aseptic environment allowing the mycelium to grow through the medium uncontested from contamination. A filter patch allows for gas exchange while preventing contamination i.e. spores or bacteria from passing through.
Once a substrate is inoculated, the bag will carry the mycelium through all the stages of growth before it’s time to fruit which is achieved by cutting the tops of the bags off, making an X in the side or removing from the bags all together. It’s species dependant. To achieve this, the bags and filters have to be made from high temperature plastics to withstand sterilisation which is achieved at 121c. The most common plastic is polypropylene often abbreviated to PP, sometimes written as PP5.
Polypropylene is a thermoplastic that is often used in the food industry thanks to it’s high melting point of 160c and wide range of properties. Some grow bags and filters are made from Polyethylene, this can’t withstand the high temperatures of sterilisation, so the substrate or spawn is sometimes irradiated with gamma rays to sterilise it or by using lower temperatures and pressures of steam for longer periods of time, known as super pasteurising.
As the bags are plastic, once full, they can be sealed by heat sealers, this process can be unreliable and sometimes requires several attempts to get bags to seal. However, some people opt to use cable ties, food clips, rubber bands, string or even purpose made clamps to seal the bags. The choice is yours.
Grow bags are only necessary for substrates that are to be sterilised. Growing oysters on pasteurised straw for example, simple lay flat polyethylene tubing can be used since you don’t actually pasteurise the bags, just the substrate. There are also special bags on the market for pasteurised substrates like these blakk brand log bags that have hundreds of pre-perforated holes.
Or these posh bin bags from unicorn.
Now you know what mushroom bags are used for. Let’s look at the three main types of gusseted bags. Just so you all know, I wasn’t sponsored to feature any product, these are just my opinions and research.
First, we have the most well-known and my favourite brand, Unicorn bags. Unicorn bags come in a variety of shapes and sizes. They have 4 different filter types A, B, T and TV however, TV isn’t a very common filter type as it’s made with Tyvek. Tyvek is made from polyethylene and can’t withstand the temperatures of sterilisation. The image below from left to right is A, B, T and TV.
Type A filters are made from Laminates of polypropylene non woven and polypropylene membrane and are 0.5 microns in pore size.
Type B filters are made from laminates of polypropylene non woven with PTFE and are 5 microns in pore size.
Type T filters are made from Laminates of polypropylene non-woven with PTFE and are 0.2 microns in pore size.
Type TV filters are made from Laminates of polyethylene non-woven also known as Tyvek and are also 0.2 microns, though I don’t have any TV Filters so hand you can see the picture from Unicorn below!
Though under the camera, the 0.5-micron filter looks the biggest, I’ve been assured by Unicorn that they are, infact, 0.5 microns! The physical filter patch size changes from bag to bag size, the smaller bags have smaller patches, the bigger ones have bigger! Shocker! The smaller filter pore size is generally used for spawn while the larger is for substrate, however, these are interchangeable and often it comes down to the users preference and requirements. If you’re just starting, the Type A filters are a good benchmark for spawn and substrate.
Unicorn have 4 different categories of bottom gusseted bags. Sizes 4, 10, 14/3 and XLS.
The smallest size is 4, these are 46.5cm by 10cm.
Next are the size 10 which are 47cm by 13.5cm.
Then you have the size 14/3. Which are 48.3 by 20cm
Finally, you have the XLS. These beasts are 48.3cm by 24cm and have the biggest physical filter patch size.
Some of these categories have variations like longer or smaller versions of the bags. For example, they have 3T L which is a slightly longer version of the 3T bags which increases its capacity.
Some of the smaller bags like the 10T have an option of a pre-installed injection port, these are 4 times as expensive as the port-less bags so you’d be better of making your own filter patch by gluing them on, using silicone or just micropore tape.
I hope its clear, but each bag category has 4 filter types to choose from so you’ve really got a broad range of combinations when it comes to Unicorn products. Unicorn also sell bio-degradable growbags, pillow bags, Oyster bags, bag clamps as well as tumblers and tissue culture pots!
The next most common are the SaCo2 bags. These are made by a company called Saco2 who are a sister company to Mycelia in Belgium. Mycelia are a huge spawn producer in Europe and distribute world-wide. The gusseted bags that Saco2 make are called Zipper bags or Micro sack but I’ll stick with zipper bags. They differ to unicorn as depending on the bag, they have 2 to 6 filter strips that run the whole width of the bags! This allows for a high and evenly distributed air exchange.
They’ve also developed them in such a way that the filters don’t transpose much moisture so the grain or substrate pressing up to the filter doesn’t dry out. The zipper system comes in two ‘widths’ called S and B. One for spawn and one for substrate, the wider one is for substrate, allowing for more gas exchange. S being Substrate and B being Spawn.
I tried to find out the actual pore size through digging around but couldn’t find any information on it, though I’d imagine they are between 0.2 and 0.5 microns, since these are the most common sizes. The only information I could find was this little description on their FAQ.
‘The S-filter gives approximately 1.5 times more gas exchange against the B-filter. This is why the S-model is mostly used for Substrate and the B-model for Spawn. Other parameters related to the gas exchange are, of course, the amount of filters per bag and the volume of the bag. Only thorough tests will tell which bag is the most suitable for which products and which bag gives the best results for your purpose.’
Saco2 have 5 different gusseted bag sizes and The way you read their codes are like this.
The first part is the plastic type PP or PE being polypropylene or polyethylene and the thickness of the plastic, 75 or 50, measured in microns.
Next is bag type. B/S denotes the filter type either spawn or substrate. E is the filter material, though this is not specified what it is. U/H/D is the filter location, either up near the top, spread out or down near the bottom, and 2,4 or 6 is the number of strips.
Finally, a V or X denotes the presence of a gusset or not, this would make them gusset or pillow bags, with the final numbers denote the dimensions in width and height.
The smallest Saco2 Bag is PP75/SEU2/V18.7-32. This has 2 filter strips and is 32cm long by 18.7cm wide.
Next is the PP75/BEH4+1/V22-49, this is the only bag with 5 filters and is 49cm long by 22cm wide.
The PP75/SEH6/V32-49 has 6 filters and is 49cm long by 32cm wide.
Then comes the PP75/BEH6/V37-53 which is another 6 filter bag that is 53cm long by 37cm wide.
Finally, is the biggest gusseted bag the Saco2 make PP50/SEU4/V40-51. This only has 4 filters and is 51cm long and 40cm wide.
Saco2 also sell polypropylene plastic boxes with the same filters built into the lids as well as huge pillow bags, sealers, bag tumblers and lid closers.
The last is the Chinese bags. I call them that because they’re not made by a single company, rather they’re sold on eBay, Aliexpress and Amazon with the same poorly photo-shopped image modified in one way or another. They don’t appear to have a single company claiming origin. The bags loosely copy unicorn bags for sizing, though they don’t follow the same sizes all the time, sometimes the stated size is different from the actual size you receive.
The filter patches are seemingly all the same both in physical dimensions and pore size which appear to be 0.2 microns and are easily distinguished by being round rather than square. The material they claim to use changes depending on the website you find them on. Some say Polypropylene, some Polyethylene and some PVC which is unusual.
Honestly, for what it’s worth, avoid the Chinese bags. It’s frustrating putting all the effort into preparing a substrate or grain only to have a bag split. As a mushroom grower you recognise that you will lose the odd bag to contamination or manufacturing imperfections, but when it becomes a regular occurrence of defects the failure accumulates over time. They also don’t work out much cheaper than the others.
The 2 winners in my books are Saco2 and Unicorn. Saco2 are more expensive but have a high quality and good pedigree being a sister company of mycelia. Unicorn are great value, great quality and have a proven track record in the mushroom cultivation world.
Many of you will want to know about bag capacities. I can’t honestly give you accurate information on this since different substrates and grains have different volumes. My only advice is to be mindful when selecting your bag sizes. It would be rather annoying to have 1000 XLS bags or PP50/SEU4/V40-51 bags turn up only to realise they don’t fit your setup!
Honestly though, don’t get too caught up or worried about the different filter sizes in the beginning. Once you’ve had some time and experience with different bags, you’ll find the ones you like, fits in with your sterilisation method and suits your size of fruiting chamber!
I’ve got a few bags for sale in my shop if you fancy a go! Cheers for this boring, long read!