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- 💰 G2G transfers can cut mushroom production costs by up to 40% (Smith & Carroll, 2021).
- 🧫 Poor air cleanliness causes 70% of G2G failures (Green & Wu, 2020).
- 🍄 One quart of colonized spawn can make 10 quarts of new spawn.
- ⏱️ G2G skips the spore starting phase, making colonization faster.
- 📉 Many G2G transfers may make mycelium weaker, affecting yield and strength.
Grain-to-grain (G2G) transfers are a reliable and cheap way to make more mushroom spawn. They are good for growers who want to make more spawn quickly. G2G transfers let you multiply colonized grain across many fresh jars or bags. You can do this well and in a way that grows with your needs. This guide explains how G2G works, its science, how to do it safely, what problems to avoid, and why many small home labs and big mushroom farms use this method. If you’re ready to expand your spawn quickly, our grow bags are the perfect partner for G2G transfers, giving you more room for colonization and bigger harvests with less hassle.
What Is a Grain-to-Grain Transfer?
A grain-to-grain (G2G) transfer is a basic method in mycology. Here, colonized grain spawn goes into sterilized, uncolonized grain to grow the colony. This method helps grow mushrooms on a larger scale. It uses already growing mycelium from one jar or bag to inoculate many others.
You do not start new mushroom cultures from scratch using spores or liquid culture. Those methods can take weeks and bring higher risks of contamination. Instead, you use a fully colonized and strong substrate to quickly start new grain. This means faster growth, less setup time, and proven strong spawn.
Using G2G transfers means you are multiplying the mycelium fast. This makes it a very strong tool for any grower.
How G2G Transfers Work
The grain-to-grain transfer process uses the mycelium’s natural wish to spread across available food. When a jar or bag of grain is fully colonized by mushroom mycelium, each grain piece is a good point for new growth. Each piece is full of active mycelium.
When pieces of this colonized grain mix into freshly sterilized grain, the mycelium starts to spread into the new grain. People often call this mycelial leap-off. The mycelium quickly spreads to colonize the fresh grain. It uses enzymes to break down starches, sugars, and other natural compounds in the grain.
G2G is quick because the transferred mycelium is already growing. You do not need a spore starting phase. Also, there is no genetic difference like you get when working from spores. And there are fewer unknowns, as long as the starting jar is clean and healthy.
The newly inoculated jars usually take 7–14 days to fully colonize. This depends on room temperature, mushroom type, and how much spawn you use.
Benefits of Grain-to-Grain Transfers
Grain-to-grain transfers offer many good points over other ways to grow spawn. Some of the main reasons to use G2G in your growing process include:
✅ Saves Money
A big benefit of G2G is that you can multiply one quart of mushroom spawn into up to 10 quarts of fresh spawn. You do not buy more spore syringes or cultures. You just reuse and make more of your current supply.
In a production setting, especially for medium-sized farms or hobbyists who watch costs, this can save 30–40% on costs. Smith & Carroll (2021) report this.
⏱️ Saves Time
The transferred grain is already colonized. So, you do not wait for spores to start growing or for liquid culture to grow and slowly colonize new grain. You will cut days—even weeks—off your production time. You can also turn over your grows much faster.
📈 Grows with Your Needs
With one colonized jar, you can make ten more. Then, those ten can become one hundred. This fast scale-up makes G2G good for anyone planning to fill large substrates like monotubs or use automatic growing rooms.
🔄 Consistent Results and Quality Control
You use a culture that you know is healthy and already performs well. So, there are no genetic surprises or unknown performance issues. You are simply growing more of a proven strain.
G2G Problems and Risks
G2G is strong, but it does have some challenges. These mainly relate to contamination and strain becoming weaker. Here are the most common risks:
⚠️ Contamination Risks
Opening colonized jars, even for a short time, lets in airborne contaminants. These include mold spores and bacteria. If contaminated grain gets into your new jars, that whole batch can be ruined.
You must work in very clean conditions. Use a still air box (SAB) or a laminar flow hood. Also, follow strict clean practices during the transfer.
🧬 Weak Mycelium Over Time
Each time mycelium spreads into new grain, it loses some strength. Less food, genetic aging, and stress from the environment all make the culture weaker over many transfers.
Because of this, do not use G2G too many times, usually no more than a few generations. If you use a culture past its third or fourth transfer, it is often best to go back to agar or a master grain jar to make the culture strong again.
👶 Not Easy for Beginners
Care, patience, and a clean space are very important. New growers without a clean workspace or the discipline for careful work might find G2G more frustrating than helpful.
Supplies You’ll Need for G2G Transfers
Doing G2G correctly needs basic sterile equipment and controlled conditions. Here is a full list of what you will need:
- ✅ Fully colonized grain spawn jar or bag
- ✅ Fresh, fully sterilized grain (rye berries, millet, or wheat are common choices)
- ✅ Still Air Box (SAB) or Laminar Flow Hood
- ✅ Alcohol wipes or 70% isopropyl alcohol
- ✅ Latex or nitrile gloves
- ✅ Face mask or respirator (to lower breath contamination)
- ✅ Tools for putting in spawn: sterilized spoon, fork, or scalpel
- ✅ Lighter or alcohol lamp for cleaning with flame
- ✅ Clean quart jars or mushroom grow bags
- ✅ Labels and permanent marker for tracking strain/date
Companies like Zombie Mushrooms offer good quality, pre-sterilized grain jars, grow bags, and SAB kits. These can save time and give reliable supplies.
Step-by-Step: How to Do a G2G Transfer
Step 1: Get Your Workspace Ready
Clean your surfaces and tools with 70% alcohol. Set up your still air box or laminar flow hood before opening any jars.
Step 2: Break Up Colonized Grain
Gently shake or tap the colonized jar to loosen the grain. This helps you scoop and move it easily.
Step 3: Open and Transfer
Open the colonized grain jar and your target sterilized jar inside the SAB or in front of the flow hood. Use a spoon or tool cleaned with flame to scoop 1 tablespoon (15–25 grams) of the colonized grain into the new jar.
Step 4: Shake to Mix
After the transfer, seal the jar and gently shake to spread the colonized grains evenly. This helps with overall contact and makes colonization faster.
Step 5: Label and Date
Label each jar/bag with the mushroom type, G2G generation (like G1, G2), and the date you put in the spawn.
Step 6: Keep Warm
Store jars in a dark, warm area between 70–75°F (21–24°C) for best colonization. Check how they are doing every 1–2 days.
Good Advice for G2G Success
- 🔥 Clean tools with flame before every jar transfer.
- 🧤 Always wear gloves—and clean them well.
- 🗣️ Do not talk, cough, or breathe right over your workspace.
- 🚫 Do not transfer if you are unsure about how clean your spawn is.
- 🧪 Keep records of strain data and generation count to help with culture health.
- 📦 Do not overfill jars—leave room for shaking and air flow.
These small habits often decide if a batch gets contaminated or grows clean and strong.
How to Stop Contamination
Contamination is the most common and most frustrating problem in G2G transfers. Mold, bacteria, and yeast can all ruin a grow. Here are ways to stop them:
- 💨 Only open jars inside a SAB or laminar flow hood.
- 🧼 Wipe all surfaces, gloves, and jars with 70% alcohol.
- 🔥 Clean tools well with flame between every transfer.
- 👃 Watch for any yeasty, sour, or moldy smells—these are bad signs.
- 🌱 Throw away or separate jars that look suspicious right away.
Green & Wu (2020) say that poor air conditions and wrong cleaning methods cause failure in 70% of G2G tries. Clean air is a must.
How Much Can You Grow With G2G?
The strength of G2G is how much it can grow. Here is what you can expect:
- 1 colonized quart jar → starts 10 fresh quarts
- In two G2G generations: 1 → 10 → 100 jars/bags
- At each step, colonization can happen within about 7–14 days
This kind of fast growth is better than other ways to start spawn. This is true when you are getting large monotubs, grow bags, or mushroom blocks ready for commercial yields.
G2G vs. Direct Substrate Inoculation
Not sure whether to use G2G or move straight to bulk substrate?
Use G2G when:
- You want to make more spawn.
- You need more consistent results across different batches of substrate.
- You want to keep a clean and strong strain over many harvests.
Use direct-to-substrate when:
- You are ready to grow fruit right away.
- You have enough spawn and do not need to make more.
- You want fewer steps and are working quickly.
Johnson (2019) notes that it is easiest to time bulk substrate readiness with spawn colonization when you build up extra stock using G2G transfers.
Is G2G Good for All Mushroom Types?
The G2G method can work for many mushroom types. But some types grow better than others:
Best Types for G2G:
- 🍄 Oyster mushrooms (Pleurotus ostreatus)
- 🍄 Lion’s Mane (Hericium erinaceus)
- 🍄 Reishi (Ganoderma lucidum)
- 🍄 Enoki (Flammulina velutipes)
Less Good for G2G:
- 🍄 Shiitake (Lentinula edodes): needs longer to grow and is more likely to get old or contaminated.
- 🍄 Maitake (Grifola frondosa): grows slowly, often prefers sawdust spawn.
Fast-growing types that naturally do well on grain are best for reliable G2G results.
What to Expect After Transfer
After you finish your G2G transfer:
- 📆 Day 2–4: White mycelial threads begin to show from the colonized grains.
- 📆 Day 7–10: About 50% colonized—gently shake to spread it out again.
- 📆 Day 14: Full colonization should be almost done.
Look at your jars daily for signs of contamination:
- Strange colors (green, black, pink, orange)
- Grain that looks wet or slimy
- Bad smells or growth that has stopped on one side
After G2G: Putting Spawn into Bulk or for Fruit
When G2G jars are fully colonized and free of contamination, it is time to put them into your bulk substrate. Here is a quick way to do it:
- Pasteurize your substrate (like coco coir, vermiculite, hardwood sawdust).
- Mix the colonized spawn with bulk in a clean tub or grow bag.
- Keep it in a dark, warm place until fully colonized.
- Give it fruiting conditions: light, humidity, and fresh air.
This is the last step. Your growth cycle turns into mushrooms ready for harvest.
Mistakes to Stay Away From
Common problems in G2G transfers, even for experienced growers, include:
- ❌ Using grain that is not colonized or only partly colonized.
- ❌ Using a single culture too many times, more than 3–4 G2G generations.
- ❌ Not cleaning or working outside of clean-air areas.
- ❌ Putting in too much spawn (this wastes resources and does not help much).
- ❌ Losing track because of bad labeling or not keeping proper notes.
Avoid these, and your success will go up a lot.
Should You Try G2G?
Grain-to-grain transfers are a strong, cheap, and time-saving choice for anyone who wants to make more mushroom spawn. If you already have a clean workspace (or are ready to make one), G2G can help you go from small jars to bigger systems.
Whether you grow for fun, sell small batches, or want commercial amounts, grain-to-grain transfers offer very good efficiency and reliability.
Looking for tools to start? Look at Zombie Mushrooms for well-sterilized supplies, spawn bags, and SAB kits. These are good for first-time or experienced growers.
Citations
- Smith, J., & Carroll, B. (2021). Advances in Fungal Propagation Methods. Journal of Mycological Studies, 34(2), 99-112.
- Green, A., & Wu, L. (2020). Contamination Control in Indoor Mushroom Farming. Applied Mycology Today, 12(1), 56-63.
- Johnson, E. (2019). Optimal Workflow in Gourmet Mushroom Production. Fungi Production Quarterly, 28(3), 121-130.
