SOP for Optimizing Hash Drying by Detecting Freeze Drying Endpoint

SOP for Optimizing Hash Drying by Detecting Freeze Drying Endpoint

Jan 24, 2024

Method initially developed by Jason Blumenkamp
Co-authored by Jason Blumenkamp and the team

Calculating time spent in ultimate vacuum is the easiest way to determine the optimal drying time for your hash.

This guide walks you through the process of figuring out what your freeze dryer’s ultimate vacuum level is during drying, running a test batch to determine Final Dry times, and the internal experiments we followed to get here.

Why Should You Do This

Better resin. Faster production.

Finding your true drying endpoint minimizes unnecessary terpene loss.

It also speeds up production by avoiding spending time drying material that’s already dry.

Over-drying hash is a huge problem for many solventless labs who currently run freeze dryers. Harvest Right machines operate in a “set and forget” style that doesn’t leave much customization in terms of process parameters. 

As an operator, you are subject to whatever the machine’s perceived definition of “dry” is.

Harvest Rights are designed for food, not hash. It’s not likely their engineers were optimizing for hash dryness when they created their Final Dry profile. 

By relying on the predefined HR recipe, most people are over-drying their hash. Hash typically doesn’t need to dry for the entire duration of the cycle. Leaving it to do so only subjects it to unnecessary degradation. 

This is a process to mitigate unnecessary terpene loss, maximize resin preservation, and create a consistent production schedule that can be scaled across different starting material and final SKUs.

Introduction to SOP

Let’s start with a cursory glance at freeze drying hash:

  • During vacuum drying, water is sublimated from the hash.

  • Water vapors form and increase pressure inside of the drying chamber.

  • When primary drying completes and free water molecules are removed from the hash, vacuum levels stabilize at the ultimate vacuum that can be achieved in the chamber.

  • As evaporation from the tray surface decreases, tray temperatures begin to match the tray temp set points in your freeze dryer software

Once primary drying is complete and unbound water is removed from the material (marked by stabilization of vacuum levels), the focus shifts to secondary drying. This phase is crucial for removing residual bound water and requires precise control to ensure hash reaches the desired level of dryness without unnecessarily damaging terpene content. The operator’s role becomes more prominent during this phase, as standard freeze dryer software may not adequately detect the subtle changes occurring during this final drying stage. 

Secondary drying

During secondary drying, so little water vapor is released that it may be impossible to measure any changes through your freeze dryer’s software.

That leaves it up to the operator to determine ideal secondary drying time.

Fortunately, it’s a relatively simple process to calculate and repeat the perfect secondary drying time if you follow the right steps. 

Using time at ultimate vacuum, correlated dry batch weight and dryness level, you’re able to develop a consistent freeze drying SOP for your lab and preserve the greatest amount of volatiles possible.

  • Time at ultimate vacuum

  • Correlated to dry batch weight

  • Dryness level

Notes from Our Experiments

Please use our internal metrics with caution. All starting material, lab environments, and techniques have slight variations that may cause different results.

Batch sizes of 100-200g dry weight required approximately two (2) hours at the ultimate vacuum levels to dry completely using a Harvest Right Large Pharmaceutical model and Oil Less Pump.

  • Ultimate vacuum level of 180mTorr was achieved.

  • Dryness was determined by the ability of the hash to freely fall through a stainless sieve with simple vibration and shaking (please note some hash might not be able to perform this style of dryness test).

More testing needs to be done to determine the optimal pump for freeze drying hash. We do know that contaminants in vacuum pump oil can negatively impact pump performance, time to pull vacuum, and ultimate vacuum level.

Be mindful of condensation when checking trays. Water can condense on your material when removing the trays from a cold vacuum chamber. If you see condensation on your trays, freeze them again and dry for additional time. 

Checking freeze drying endpoints like this is well-tested and has been used in other industries for years. Multiple freeze dryer companies offer forms of dryness detection. Most take a software based approach, but Labconco offers a form of dryness endpoint detection based on material temperature monitoring with their freeze dryers. If you would like to read more about endpoint monitoring, check out “LYOPHILIZATION – Process Monitoring During Freeze-Drying”.

Several hash companies have published a lot of great information about freeze drying, and we recommend doing your own research in coordination with this basic SOP to increase your chances of success.

Keep a lab book, record observations from your experiments, and let the community know when you have a breakthrough with the drying process. 

Procedure for Identifying Hash Drying Endpoint

Here is the full process for identifying optimal drying time based on ultimate vacuum. Please keep in mind that starting material will behave differently depending on how it’s cultivated, washed, and prepared. It is recommended to retest when changing batch sizes or types of resin.

  1. Run a batch and record the lowest vacuum pressure you observe during the drying process.

  2. After the standard cycle completes, remove your trays/product and start the vacuum system. Record vacuum pressures with the empty tray rack after 15 min, 30 min, 45 min, 60 min, 90 min, and 120 min. 

    • Click ‘MORE TIME, DO NOT DEFROST’ on Harvest Right units

    • Some time around 45-90 minutes the chamber should reach the ultimate vacuum level the system can achieve.

    • Note if this is the same pressure achieved during a typical timed run. If your vacuum system is working properly the two hour point is long enough to verify the system is at the ultimate vacuum level. You must record this pressure with the chamber at the same temperature as a standard run. 

  3. The initial dry time optimization is performed with only one tray, evenly loaded with a thin layer of hash that fills up the entire surface area. 

  4. Record tare weight of tray with any liner.

  5. Record the weight of the loaded tray with the hash and water. This is used to calculate the amount of water in the hash. 

    • Customize the freeze dryer setting to maximize the dry time and start the drying process.

  6. Shelf temperatures below 35°F are recommended. Lower shelf temperatures preserve volatiles, but may increase drying time. We typically see shelf temps ranging from 20°F to 40°F. Jason often runs his freeze dryers with no temperature or below 30°F.

  7. Set your freeze dryer software to the maximum programmable (Final Dry) time, so that you can end the process manually based on vacuum and temperature data.

  8. Start the drying process. Diligently monitor the vacuum progress and record the time and vacuum readings at set time intervals. 

    • Check every 30-60 min at the beginning of the process and more frequently (every 10 min) towards the end, as you approach the ultimate vacuum level you previously recorded.

    • There are third-party devices that can remotely monitor your freeze dryer, making it a lot easier to check your process and record the data.

  9. Once the ultimate vacuum level is achieved, set a timer for a specified amount of time (we used 2 hours) and check your product for dryness when that interval is complete. If more drying time is needed, add at least 45 minutes (this allows the system to achieve ultimate vacuum level again, plus enough time to remove remaining moisture).

  10. Record the dry weight of the hash in the tray by subtracting the tare weight. 

    • This data is used to correlate batch size to secondary drying time at ultimate vacuum. 

    • The calculated water weight can help estimate the amount of time for future primary drying cycles.   

The ultimate vacuum level on your particular freeze dryer will change over time due to vacuum seals, pump performance, and other physical variables. 

If you want a much simpler way to do this, use a HashyLink to record the vacuum levels to avoid constant trips to the freeze dryer during testing. 

Once you do determine the duration your batches need to spend in ultimate vacuum to achieve dryness, HashyLink again enables you to measure the time before your check without being in front of your freeze dryer’s screen the entire time.

Conclusion and Further Questions

More data is needed to make recommendations for secondary drying times. We would like to do follow-up experiments with moisture meters to see if they can aid with any real-time prediction. Drying times are dependent on a wide range of variables from cultivar to scoop size and technique. There’s a lot of factors at play, and it’s important to keep as many aspects of your process constant as possible when experimenting with different drying parameters. 

Contact HASCHRU@GMAIL.COM for consulting.

Visit for a simple freeze dryer monitoring device.

This is an open invitation to other companies who want to collaborate with us to study freeze drying of hash in more detail. If you’re a processor or equipment company with a deep interest in drying hash, send us a message to connect.

From the Hashy crew…

On Shelf Temperatures and Vacuum Pumps

Shelf temperatures have trended downwards over the last few years as hash makers increase their understanding of volatile terpene preservation. On the vacuum side of things, pulling a very deep vacuum may actually lead to increased dry times. It’s been assumed that you want to achieve the lowest vacuum possible, and while that may be true on some units, it might be detrimental to condenser capacity. 

On Harvest Right and Labconco units, this is something to be particularly mindful of. Our working definition of ultimate vacuum is currently as low as it will go, but in the future, this might be further optimized based on chamber size and how quickly your condenser is able to work. 

Working on this SOP has been a really exciting process. We’re happy to bring some real data to the table and work with hash makers all over the world to increase our understanding of what dries the best resin.

The most important thing is to follow a basic process for experimentation and record your results. Guessing and checking makes it a lot harder to make fire hash on a consistent basis. 

– Chase

© 2024 CSKD, LLC. All rights reserved.

© 2024 CSKD, LLC. All rights reserved.