What is Master's Mix?

Growers use Master's Mix for its big first flush and because one recipe suits most wood-loving species, including oyster, lion's mane, chestnut, shimeji and enoki. GroCycle, a company that sells growing kits and courses, credits T.R. Davis of Earth Angel Mushrooms with the recipe. Davis tried 10% to 70% soy hulls and settled on 50%: more raised the risk of contamination and deformed mushrooms, and less cut yields (GroCycle).

Cornell's Small Farms Program says sawdust or pellets mixed with wheat bran or soybean hulls is what most specialty growers fruit on, and gives the highest yields. It needs steam sterilization and a lab for inoculation (Cornell).

Make Master's Mix by mixing equal weights of hardwood sawdust and soy hulls with water, bagging it and pressure-sterilizing it. GroCycle's recipe for one 5-lb block (GroCycle):

1. Measure. 1 lb (453 g) of hardwood sawdust and 1 lb of soybean hulls, or 2.5 cups of each as pellets, plus 1.4 liters of water.
2. Hydrate. Soak the soy hull pellets in 700 mL overnight, and the hardwood pellets in the other 700 mL for 30 minutes.
3. Check moisture. Squeeze a handful lightly. More than a drop or two means it's too wet; see field capacity.
4. Sterilize. GroCycle gives 2.5 hours at 15 PSI. Midwest Grow Kits, which sells Master's Mix pellets, gives 3.5 hours at 250°F (15 PSI), longer for big loads (Midwest Grow Kits).
5. Cool, then inoculate clean. Cooling in the cooker can take up to 8 hours. Inoculate with grain spawn in front of a flow hood, or in a glove box such as a still air box.

For what bags, pellets and spawn cost per block, see our cost per pound guide.

Master's Mix is one supplemented sawdust recipe among several. The others in these sources use bran instead of soy hulls:

Recipe	Wood	Supplement
Master's Mix	50% hardwood sawdust	50% soy hulls
GroCycle sawdust mix	60% hardwood sawdust, 20% wood chips	18% bran, 2% gypsum
Stamets' recipe (via UC)	73% oak sawdust	24.6% bran, 2.4% gypsum
Oregon recipe (via UC)	76% oak sawdust	12% millet, 12% bran

Sources: GroCycle, UC Cooperative Extension. GroCycle says shiitake does better on sawdust with a little bran, because Master's Mix carries too much nitrogen for it, and that many growers find 5–15% supplement best for reishi (GroCycle).

• Pasteurizing it, or using it in an open tub. Midwest Grow Kits says it is a sterilized substrate, "not for open tubs or pasteurization" (Midwest Grow Kits). See sterilization vs pasteurization.
• Mixing it too wet. Overhydrated substrate is the most common cause of slow colonization, GroCycle says.
• Inoculating it warm. GroCycle warns that substrate that hasn't cooled can kill the mycelium.
• Expecting an even second flush. GroCycle finds the second flush often weaker than on sawdust and bran, though the first usually makes up for it (GroCycle).

Hypha keeps your Master's Mix recipe with your supplies in its inventory, and compares each strain's success and contamination rates.