Preparing to pelletize hops
by Courtney Llewellyn
While Washington, Oregon and Idaho are well-known as the top hops-producing states in America, the number of hop farms outside of the Pacific Northwest continues to grow. That may be one of the reasons why Penn State Extension recently hosted a series on hop pellets and considerations for farm-scale production.
The first session was led by Dan Ciolkosz, Ph.D., of Penn State’s Department of Agricultural and Biological Engineering. He provided an overview of the pelletizing process for farmers already growing hops.
A pellet is simply densified, cylindrical, compacted material. In the ag sector, it’s often seen as a form of wood, feed and food pellets. So why pelletize hops? “It’s related to customer preference,” Ciolkosz explained. Their higher density means they take up less space, they have a longer shelf life and they’re easier to store and transport. Their handling and flowability means they’re less like to cause clogs. “And it’s reputed the aroma release is greater” from pellets versus whole hops, Ciolkosz added.
The key to the whole pelletizing process is the squeezing action of the roller into the die. A pelletizer cools and hardens the pressed material. Ciolkosz said most biomass already has a natural “glue” that will hold things together when pressure and heat are applied.
The necessary equipment comes in a variety of sizes and configurations. Smaller equipment tends to use a flat plate die; larger equipment will use a ring die.
The Pellet Process
If you want to make hops pellets, first you need to prepare your feedstock. That means grinding/milling the hops and making moisture level adjustments, keeping 8% to 10% moisture generally. Then you’ll want to prepare your equipment, cleaning and checking roller pressure before starting things up.
Next, you’ll actually run the machine. Make sure you follow safety procedures. Run a pre-mix through for a warmup and check your feed rate before adding your hops. (Use the pre-mix to clean out the pelletizer at the end of the process too.)
When you’re done, cool and dry your pellets on a rack or in a bin for storage.
Pellet Problems to Avoid
Like any other ag process that involves machines, problems may arise. Ciolkosz broke them down and spoke of ways to remedy them.
- Washthrough – This occurs when pellets don’t form, and it’s often caused by lack of back pressure (which in turn is caused by not enough moisture or improper die configuration).
- Clogging – This happens when there’s too much back pressure in the die. The pellets just don’t move through. To fix washthrough and clogging, adjust your moisture controls and your die configuration.
- Low durability – Hops pellets can afford to be a little softer than other materials, but if they’re too soft, they’re moving through the die too quickly. Slow down the feed rate.
- Quality degradation – If the die gets too hot, it can lead to oxidation and the off-gassing of aromatics. To fix this, adjust the feed rate – or active cooling is an option. Ciolkosz said 60º C (140º F) is the absolute top temperature you want to reach while forming pellets.
Is it worth it to pelletize hops? Ciolkosz said the cost is about $60 to $120 per ton of pellets produced. But “even a smaller scale pelletizer can handle multiple farms’ products,” he noted, which means if you do decide to dive in, you could offer your services to other growers nearby for a fee.