Rye grain (sometimes called rye berries) is a great choice for grain spawn; most varieties perform well on it, it’s easy to find and relatively low cost.
Rye will expand to around x1.7 its original weight, so to prepare a 1.5kg bag of grain spawn you’ll need 880g of dry grain. Or to work backwards you’ll need around 60% of the intended weight in dry grain.
You will also want to choose a bag with a low micron filter to prevent contamination (anything under 0.3microns is suitable for grain spawn). The Unicorn 10T bags are great for 1.5kg of grain and the SAC O2 T-filter 32x42 is perfect for 3kgs.
There are 4 steps to preparing grain spawn:
1) hydrate the grain
2) cook the grain
3) dry the grain
4) sterilise the grain
1) hydrate the grain
Hydrating the grain should be done 18-24hrs ahead of cooking, this allows any dormant spores of mould or bacterial to germinate so the sterilisation process will be more effective.
- Weigh out 60% of your intended final weight in dry grain
- Put it into a pot and fill with cold water, covering the grains by about 2-4 inches
- Leave it overnight
If you don’t manage to get to your grain within 24hrs, don’t worry, depending on the ambient temperature it may be ok for up to 48hrs; however, if the grain has a sour smell or there are visible sprouts you should start over.
2) cook the grain
- Drain and refill the pot with fresh water, the grain will expand a significant amount so it’s best to have the water level around 5 inches higher than the grain
- Heat the pot until the water begins to boil
- Simmer for around 10-15mins
The amount of time the grain takes to simmer can vary, it’s best to check its progress regularly (every couple of minutes). When it’s perfect the grain will look translucent, plump and a white germ will be clearly visible at one end; a couple of kernels may have burst open. This the ideal time to remove it from the pot.
It may take a few attempts for you to get this right but don’t worry if it’s not perfect, often it will still work to some extent. If you undercook the grain your colonisation times will be longer and some strains may stall. If you overcook the grain many kernels will burst and your grain bag will be mushy, increasing the risk of contamination.
3) dry the grain
Drying the grain reduces the risk of contamination by preventing standing water in the bag.
Ideally the grain should be spread out in a thin layer allowing the water to evaporate off as steam. You can make a large colander out of mesh or some paper towel on a tray or worktop will work fine.
This takes 30mins to an hour and you should move the grains around occasionally.
Once the surface of the grains is visibly dry and no steam is coming off them they are ready to sterilise.
If you are unsure whether the grains are dry enough you can place your open palm on top of them, if they are sufficiently dry only a couple will stick to it.
4) sterilise the grain
- Weigh the grain into bags and fold over the top, push down firmly to remove any trapped air (air pockets can cause the bag the burst during the sterilisation process)
- If you’re using a unicorn bag do not use the gussets, instead fold the sides flat
- Arrange the bags in your pressure cooker or autoclave so that the steam can circulate around them, place the bags fold-down, so that the weight of the bag is holding itself closed
- Sterilise the bags for at least 90mins at 15PSI or 121ºc
If you are doing 3kg bags or a large run of multiple bags you should increase the sterilisation time to 3hours.
You’ll want to wait until the bags have cooled before inoculating them in a clean environment.