How Does a Freeze Dryer Work?

Todde Philips   

🇺🇸 Retired veteran, father, rock-climbing expert & rosin connoisseur

Freeze dryers have grown in popularity in recent years, as solventless extraction artists are constantly improving on the quest to produce the world’s best bubble hash. For commercial and craft producers alike, freeze dryers present the most optimum solution to quickly and thoroughly dry fresh ice water hash. For decades, other methods have been successfully used to dry wet bubble hash, but in terms of overall quality and terpene preservation freeze dryers offer a better solution than the other approaches. 
While traditional means of drying ice water hash rely on the process of evaporation, whereby liquid moisture in the hash changes to a gas as it escapes into the open air, freeze dryers rely on an altogether different process. And the technology behind freeze dryers doesn’t utilize any solvents or synthetic products to react with the hash. Freeze dryers simply create the ideal environment for wet bubble hash to dry. 

When Are Freeze Dryers Used in Solventless Extraction?

After ice water hash is extracted from either fresh frozen or air dried cannabis flowers it’s thoroughly soaked with water. The hash is very difficult to work with in this form, and looks like an amorphous blob or a wet patty. Storing hash when it’s in this state will invite mold growth, which will render the hash unusable. Immediately after the hash is extracted, it’s important to thoroughly dry it before it’s put away for curing and storage, or rolled into a Temple Ball

One of the traditional ways to dry these wet hash patties include freezing the patties so they are solid and then breaking them down into a powder to dry on parchment-lined cardboard. This drying process of grinding the hash into a sand-like texture and then leaving to dry in the open air will take several days, invite oxidation, and lead to terpene loss. Drying hash like this is also inconsistent, as moisture can remain present in small pockets within the hash and trapped in the thicker chunks of the hash. Different pieces of hash will dry in the air at different rates, which makes air drying quickly more difficult. 




Advantages of Freeze Dryers

When it comes to drying hash, speed and thoroughness are central to the process. Freeze dryers provide the perfect answer to drying wet ice water bubble hash. 

Freeze dryers pull the moisture out of wet hash quickly and evenly. They reduce the amount of oxidation that occurs in the hash since the whole drying process is finished in just 24 hours or less. Since less oxidation takes place, the original color of the hash is also maintained. Often, air dried bubble hash is darker because of the amount of oxidation that takes place. Oxidation causes hash to turn a brownish color, which is a natural effect of oxidation. 

Freeze dryers completely eliminate moisture, preventing any wet pockets from remaining in the hash. Areas of moisture will harbor mold, so fully removing all moisture is a big win. They also minimize operational space, since the hash doesn’t have to be spread out so thinly over a large surface area in order to effectively air dry. 

Finally, freeze dryers allow the extractor to skip the step of grinding down the wet hash into the smallest pieces possible, in an attempt to let the hash thoroughly and evenly dry in the air. Microplaning or sieving wet hash is necessary to prepare it for air drying. This is a labor-intensive and tedious step that often leads to some wasted hash. With freeze dryers, there’s no need to break the wet hash into a sand-like texture. You can leave the hash in globs on a tray and put that straight into the freeze dryer, without preparing the hash through microplaning or sieving. 

One good tip is to make the wet patties all the same thickness before they go into the freeze dryer. This is the extent of the prep work needed for drying with a freeze dryer. 

In summary, freeze dryers save time and labor, reduce oxidation, and more thoroughly dry the freshly-made, wet bubble hash. They also cause less structural damage to the hash than other methods would entail, such as dehydration or even grinding with a microplane. 

Disadvantages of Freeze Dryers


The advantages of freeze dryers outnumber the disadvantages. There is one main disadvantage though, but it doesn’t have anything to do with quality or performance. The number one disadvantage is the price point of freeze dryers. Freeze dryers start at around $3,000 for the smallest size. But given the advantages, they justify the cost for hash makers who produce more than just a little bit for personal use. 



Freeze dryers also bypass an element of the artistry involved in solventless extraction. While the lack of manual preparation and handling for the drying process is considered a win for most people, others might look at this lack of artistic touch as a disadvantage. Sieving or microplaning wet hash does require a level of artistry and expertise to do it right, and if that is something you value, you’ll miss doing it when employing freeze drying technology.

Another disadvantage is the energy and maintenance costs of a freeze dryer, although this is generally insignificant for most operations. Freeze dryers don’t require a lot of regular, expensive maintenance. 

How Freeze Dryers Work

Freeze dryers may look like food dehydrators or small ovens, but they’re a lot more advanced! 

At the center of freeze dryer technology is the process of sublimation. Sublimation is a phase change, the transition of a substance from a solid to a gas without first passing through a liquid state. Similar to evaporation, except that evaporation is when a liquid changes to a gas. In contrast to air drying methods, freeze dryers use sublimation rather than evaporation to remove the moisture, which results in higher quality outcomes for the hash. 

Vacuum technology is also utilized in freeze dryers. The vacuum environment created inside the machine expedites the sublimation process, literally pulling the moisture out of the hash in a gaseous form. 

The steps to freeze drying include

  • Preparation 
  • Freezing Phase 
  • Primary Drying 
  • Secondary Drying



For preparation, wet hash is placed onto trays lined with parchment paper, ideally in patties that are of a similar thickness. The patties don’t need to be the same size, but they should be the same thickness. This ensures the most even and consistent drying possible. 

During the freezing phase, the hash is cooled below its triple point, which is the temperature and pressure at which gas, liquid, and solid can coexist in thermodynamic equilibrium. This is normally in the range of 30-50 degrees Fahrenheit below zero for hash. This is an important setting to ensure that sublimation rather than melting will occur in the following steps.

Next is the primary drying phase, when heat is applied and pressure is lowered. To optimize for terpene preservation, a heat setting in the range of 45-55 degrees Fahrenheit is useful. Pressure is lowered by creating a vacuum inside the machine, which speeds up the process of sublimation. During this primary drying phase, about 95% of the water in the material is sublimated.

The secondary drying phase is simply building on top of the first. During this phase, the machine removes the unfrozen water molecules that remain in the hash. The pressure can be lowered even more and the temperatures raised slightly. Aiming to keep the highest temperature under the 55-degree mark is beneficial for terpene preservation. At the end of this second drying phase the remaining moisture content will be extremely low, somewhere around 1-4% of the original water content. 





Drying freshly-made, wet hash is one of the trickiest parts of the entire ice water extraction process. While air drying hash can work fine and produce a high quality product by itself, it requires the additional step of grinding down the hash into a sand-like texture and spreading it thinly across a surface to let the moisture evaporate naturally over the course of days and weeks. Air drying hash also leads to more terpene loss and oxidation. 

Freeze drying technology offers hash makers an easy, fast, and efficient way to dry hash, in a way that preserves both terpenes and original color. Freeze dryers allow extractors to skip the step of microplaning or sieving the wet hash in preparation for drying and offers a mostly hands-off approach to the process of drying. 

As drying is such a vital part creating premium quality ice water hash, any improvements in the process should be seriously considered. Whether you’re a commercial or a home operation, consider freeze dryers a big win for your solventless extraction efforts. 

What do you consider to be the greatest advantage of using freeze dryers for bubble hash? Let us know in the comments!




What is sublimation?
Sublimation in hash occurs when the moisture contained within goes from a solid (ice) to a gas without passing through the liquid state. Sublimation is used in freeze dryers to thoroughly and efficiently remove moisture while causing minimal degradation to the hash. 

Is a freeze dryer worth it for in-home processors?
If it’s within your budget, freeze dryers are definitely worth it for home and hobby processors. They are effective at maintaining high qualities in freshly made bubble hash. For commercial processors it’s basically a requirement.

How long does freeze drying wet hash take?
Freeze drying wet hash only takes about 24 hours, much less time than air drying. 

How much does a freeze dryer cost?
Freeze dryers start at around $3000, well worth the cost for most solventless extractors who prioritize quality over all else. 

What temperature settings should you use for freeze drying bubble hash?
Temperatures should not exceed 45-55 degrees Fahrenheit during the drying phase in order to preserve terpenes.



paul knight

Generally, how long is the vacuum pump on during this process?


What is the rough % of weight reduction from wet hash to dry hash?


Hi Todde, thanks for the excellent article. Some questions: 1- you mention during freezing “This is normally in the range of 30-50 degrees Fahrenheit below zero for hash”. Do you mean the temperature should be set to 35 F? 2 What are the pressure setting during main drying? 3- Should I extract enough has to fill up all the trays before starting the drying? I guess during drying the Freeze Dryer door should not be opened and closed or I can add to the material inside the freezer as they get prepared? I appreciate your comments.

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