🥥 CVG Recipe Calculator

Get a clean 5-gallon (20-litre) bucket with a tight-fitting lid. Insulated coolers or foam-lined buckets retain heat longer and improve pasteurisation effectiveness.

Break up the coir brick and add to the bucket with vermiculite and gypsum. The gypsum (calcium sulphate) helps prevent the substrate from becoming compacted after hydration and improves particle separation.

Bring the calculated water volume to a full rolling boil. Boiling water at 100°C will initially heat the substrate mixture to approximately 80–90°C at the centre — within the pasteurisation range — before cooling.

Pour boiling water over the dry ingredients. Stir briefly to ensure the coir is submerged, then seal the lid tightly. Wrap the bucket in a thick blanket or towels to retain heat as long as possible. The substrate needs to hold above 65°C (150°F) for at least 60 minutes to achieve effective pasteurisation.

Leave sealed for a minimum of 6–8 hours, preferably overnight (12–16 hours). Do not open early. The extended sealed rest period allows both the thermal pasteurisation effect and the slow rehydration of coir fibres to complete.

Open with clean gloved hands. Mix thoroughly — the bottom layer is often drier than the top. Perform the squeeze test: grab a large handful and squeeze firmly. Three to five drops of water should emerge. If water streams freely, spread on a tray to dry slightly. If no drops emerge, add a small amount of water and mix again. CVG at correct field capacity is ready to use immediately or can be stored sealed for up to 24 hours before spawning.

Coco coir is the shredded fibrous husk of coconuts. It is an agricultural waste product, which makes it extremely affordable. Nutritionally, it contains small amounts of lignocellulose that mycelium can slowly digest, but its primary function in CVG substrate is structural and hydrological. Coir fibres hold water extremely well — up to 8–9 times their dry weight — while maintaining air pockets that prevent anaerobic conditions. This makes it the ideal base material for a substrate that needs to stay evenly moist for weeks.

Vermiculite is an expanded mineral (hydrated magnesium aluminium silicate) that is completely inert — mycelium cannot digest it or derive nutrition from it. Its role is physical: the irregular, angular particles prevent the coir from compacting into a dense mat, maintaining the porosity and gas exchange channels that healthy mycelium requires. Vermiculite also holds water in its layered structure and releases it slowly, acting as a buffer against rapid moisture loss between mistings.

Gypsum (calcium sulphate) performs two functions. First, it acts as a soil conditioner that prevents the substrate particles from clumping and sticking together after hydration — a property called flocculation prevention. Second, it provides calcium, which helps stabilise cell walls in the mycelium during rapid growth phases. The quantity used in CVG is small (approximately 1 tablespoon per standard recipe) but the improvement in substrate texture and workability is noticeable.

Field capacity is the moisture level at which substrate holds the maximum amount of water without free water being present. Above field capacity, water fills the air pockets in the substrate, creating anaerobic zones where bacteria thrive and mycelium cannot grow. Below field capacity, the substrate lacks sufficient moisture to support sustained mycelium growth and will dry out rapidly during fruiting. The squeeze test is the standard field capacity test because it directly measures whether free water is present without requiring any equipment.