Unicorn 4T — Mushroom Grain Spawn Bag (Small)

The Unicorn 4T is the standard grain spawn bag for batches up to 1kg — compact, reliable, and the bag most UK growers reach for first. Whether you're running rye, oat grain or wheat berries, it handles autoclave and pressure cooker cycles cleanly with no warping or seal failure. Made in the USA since 1990 by Unicorn Bags LLC, the industry's most trusted name in mushroom cultivation bags.

Specifications

• Filter: 0.2 micron T filter — tight filtration for grain spawn, minimises contamination risk during colonisation
• Capacity: 400g – 1kg of grain
• Size: 4" × 3" × 18"
• Material: 3.0 mil polypropylene — autoclave and pressure cooker safe at 121°C / 15 PSI
• Side-gusseted, reinforced bottom seal

Why growers choose the 4T

• The 0.2 micron T filter is the tightest in the Unicorn spawn range — ideal when you want to minimise contamination pressure on smaller batches
• Compact footprint means you can fit more bags per autoclave run
• Perfect for hobbyists, small lab setups, and anyone working in the 1kg grain range
• The same bag we've been running our own grain spawn in since 2021

Ready to scale up? The 10T holds up to 1.8kg, the 3T up to 3kg, and the XLST up to 6.8kg — more grain per run, same trusted 0.2 micron T filter.

Need substrate bags instead? See our fruiting bag range.

In stock at our Glasgow warehouse. Dispatched same or next day.