Testing the Hash Vac Method For Drying Hash

What Is the Hash Vac Method?

The Hash Vac Method is a technique for mechanically removing excess water from bubble hash by applying vacuum suction beneath a sieve screen. The suction helps pull away free water while airflow across the screen increases evaporation. The idea is that this can significantly reduce overall drying time, whether you’re finishing in a freeze dryer or air drying.

Our team at Lowtemp worked together with TS Labs and Tryptomics to put this method to the test and give you real results as opposed to anecdotal advice. We tried it not once but twice in order to give you the most accurate results. This article will focus on part 2 as the most comprehensive experiment. 

Hash Vac Experiment Goals

• Goal 1: Determine if the Hash Vac method actually reduces drying time in practice

• Goal 2: Determine if it negatively affects terpene and cannabinoid content

Defining success: With any new tech, our end goal is to put real-world results behind the hype and help push the industry forward. We’d call the Hash Vac method a total success if it meaningfully cuts down freeze dryer time without drastically impacting yield or end quality negatively. 

Equipment Used in the Hash Vac Experiment

• LeBrew Aqua Gauge - to measure moisture levels 

• 6HP wet dry shop vacuum with 2.5 inch hose and bristle brush head attachment

• Delmar brand dust separator with a five gallon bucket. 

• 90µ stainless steel screen 

• Shop Vac Dust Collector with a 5 gallon bucket.

HashCru’s website has a full list of recommended equipment as well as instructions on building the vacuum system. We varied from their list slightly by using our own 90micron screen from the Lowtemp Auto-sieve. We also did not use the clear plastic cover as our lab had an optimal environment for air drying although we see why it was recommended if you do not have a safe, dark dry space. We also opted not to purchase the optional LED lights.

Test Parameters and Starting Material

Starting Material

• Strain: Outdoor-grown Fruitopia

• Wash size: 30 lbs

• Material type: Ice water hash (bubble hash)

Bubble Bag + Screen Setup

• Hash was first run through: 

• 220µ bag

• 160µ bag
  

• Vacuum drying step was performed on:

• 90µ screen

Environmental Conditions

• Lab temp: 55°F

• Air dry storage: In the dark, in a safe in the lab

• Room humidity reading (lab): 2.5% humidity (meter reading)

Experiment Design

All of the flower was washed together as one batch. After the wash, all material went through 220µ and 160µ bubble bags. That’s where the separation started.

Split #1: Control vs Vacuum Group

Following the 160µ collection, we split the batch into two groups:

• Group A: NonVac Freeze (Control)
  This portion was run through a 90µ bubble bag and then placed directly into the freezer to prep for freeze drying. No vacuum step was used.
  

• Group B: The Hash Vac Test Group
  The other portion was placed directly onto a 90µ AutoSieve screen, where the vacuum process happened.

Vacuum Process Parameters: The Hash Vac test group was transferred to our 90µ AutoSieve screen. We poured RO water over the hash to spread it into an even, thin layer across the screen, targeting a thickness of approximately 1–2 mm. This was a key recommendation from HashCru to help prevent trapped moisture. We then vacuumed the sample for approximately 90 seconds. After the first vacuum pass, the hash measured at 0.783 AW. To reach HashCru’s recommended target of below 0.6 AW, the vacuum process was repeated for another ~90 seconds. After the second pass, the vacuumed sample measured at 0.420 AW.

Important note: Water activity (AW) is a measurement used to determine whether microbial growth is possible. Most molds, yeasts, and bacteria cannot grow below ~0.60 AW, which is why that number gets referenced so often. 

Split #2: Vacuum Group → Air Dry vs Freeze Dry

After the vacuum step, the vacuumed hash was split again into two finishing methods:

• Vac Freeze: vacuumed hash → freeze dryer

• Vac Air: vacuumed hash → air dry

The vacuumed freeze dried sample (referenced in the video as Vac Freeze) completed an expedited freeze dryer cycle in just under nine hours, finishing at 8 hours and 45 minutes. In comparison, the non-vacuumed control required a full 19-hour freeze dryer cycle, meaning the vacuumed sample finished roughly 10 hours faster!

The vacuumed air dried sample (Vac Air) was moved into the lab’s safe as it was the darkest most controlled environment in the facility. The lab was kept at 55 degrees and ambient humidity during drying measured 2.5%. The air dry process took roughly two days (50 hours). 

The Test Results

After the drying process was complete, we collected two grams from each sample group for analysis at Tryptomics, a third party testing facility. All samples were submitted as bubble hash. The groups tested were:

• NonVac Freeze – non-vacuumed, freeze dried (19 hours dry time)

• Vac Freeze – vacuumed, then freeze dried (8h 45m dry time)

• Vac Air – vacuumed, then air dried (~50 hours dry time)
  

We’re including the full Certificates of Analysis below so you can review the raw data yourself. For those who just want the high-level comparison, we’ve also summarized the key results in a simple table.

Download links: NonVac Freeze, Vac Freeze, and Vac Air.

Conclusion of The Hash Vac Method

1. Did Using the Hash Vac Reduce Dry Time? 

Yes, the Hash Vac method significantly reduced drying time. For labs running a lot of food-grade material, this is a cost-effective and relatively easy way to cut back on freeze dryer time. While we did not run a non-vacuumed air-dry control, we can confidently say it also reduces air-dry time and lowers water activity below critical microbial thresholds prior to air drying.

From a pure workflow and throughput standpoint, this is a meaningful efficiency gain, especially for labs running multiple loads per week.

2A. How Did the Hash Vac Method Affect Cannabinoids?

The Hash Vac method didn’t seem to have a really negative impact on cannabinoids overall. In fact, the vac freeze sample tested nearly the same. It is hard to draw conclusions on Vac Air Dry without a control, as the total loss in cannabinoids could have more to do with the air drying process. 

2B. Did the Hash Vac Method Affect Terpenes?

The short answer is yes, it did have an impact on terpene concentration. We observed a 9.7% reduction in total terpenes when comparing the non-vacuumed freeze dried control to the vacuumed freeze dried sample. The more important question, though, is whether that difference was noticeable to the end consumer. In informal sensory testing with Matt and Hunter, our dab testers, the results were split 50/50. 

Final Thoughts

It’s worth saying this upfront: Lowtemp has little to no foothold in the freeze dryer game. We don’t make our money selling them, and we’re not here to protect freeze-dryers as the status quo. They’re a necessary part of solventless production, but they’re also often a bottleneck and a pain point for a lot of hashmakers.

That’s exactly why we’re interested in new techniques like the Hash Vac method. Not because they’re perfect, but because they challenge the way things have always been done. As with all of our testing, our goal is to share real results, not push a narrative.

Altogether, the HashVac method shows real promise for home hashmakers that don’t have a freeze dryer and are looking for a quick and cheap way to air dry. It also shows a serious potential for anybody looking to speed up their dry time in freeze dryers. 

The small loss in terps could potentially be worked out by dialing in your freeze dryer settings, and ensuring there is no overdrying of your bubble hash. Check out our guide to drying bubble hash to properly dry your bubble hash.

Now we want to hear from you. Have you tried the Hash Vac method? Did it improve your workflow? Did it affect the quality of your end product? Let us know what you’ve seen. Shoot us an email or tag us on social.

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