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Impact of different flushing times on quality and taste of cannabis

Many cannabis growers implement a flushing period in the final days to weeks before harvest in order to improve the taste and quality of the product. “While many cultivators attest to the effects of a flush, no scientific studies have been conducted to validate this practice,” the Rx Green Technologies team says. Therefore, the company has undertaken a study to determine the influence of different flushing times on the chemical profile, flavor, and combustion characteristics of cannabis. “The results of the trial indicate that there is no benefit to flushing cannabis flower for improved taste or consumer experience.”

For the trial, the cannabis variety Cherry Diesel was grown at the Rx Green Technologies R&D Facility using Rx Green Technologies nutrients and Clean Coco. The first flushing period began 14 days before harvest. The other flushing periods were ten, seven, and zero days before harvest. Each flushing period was tested on 12 different Cherry Diesel plants divided into four different groups (replications) spread evenly across the flowering room tables. Flower and fan leaf samples were collected from each flushing treatment on the first day of flush and the day before harvest to quantify concentrations of essential plant nutrients. After harvest, trial plants were cured before determining the final trimmed flower weight, terpene, and THC concentrations.

To determine smoking flavor and characteristics, samples of each flushing period were distributed to cannabis industry experts in a blind taste test. Each participant received one sample of each flushing time without the knowledge of its treatment. Participants were asked about their personal cannabis flavor preferences before tasting. After tasting, participants were asked to rate the sample for flavor, harshness of smoke, and color of ash.

Fan leaves collected from Cherry Diesel plants the day before harvest. Flushing times depicted are (a) 14 days, (b) 10 days, (c) 7 days, and (d) 0 days.  

The results of the trial show that visual differences in fan leaves between flushing times were apparent the day before harvest. Plants flushed for ten or 14 days had leaves that were more yellow, necrotic, and dry than plants flushed for zero or seven days. The color of the 14 and ten-day flushed leaves indicates a greater breakdown of chlorophyll in the plant, leading to reduced greenness.

Concerning the flower weight, THC, or terpenes in Cherry Diesel, flushing times did not have an impact. Flower samples were taken the day before harvest were also analyzed for the content of essential plant nutrients. Overall, there was no significant change in the mineral content of the flower as a result of different flushing treatments. In cannabis flushed for 14 days, nitrogen was 6.7% lower than in the zero-day flush treatment. Continuing to feed nitrogen can increase its concentration in the plant, reducing the need for the plant to use its reserves for essential functions. Phosphorus, potassium, calcium, magnesium, and sulfur were similar for all four flushing treatments.

There were changes in iron concentrations due to flushing treatments. Iron was at least 50 ppm higher in flower flushed for 14 or ten days. Small changes were observed for zinc as well. Zinc was approximately 73 ppm higher in flower flushed for 14 days. The fluctuation in zinc did not follow a consistent pattern like iron. There was no significant change in manganese, boron, copper, or molybdenum. Nutrients like iron and zinc can accumulate in growing media over time. Feeding water during a flush may release some of these nutrients from the media into the plant. Additionally, zinc and iron are involved in the breakdown of chlorophyll occurring during senescence.

Overall, the duration of the flushing period had no impact on the flavor, smoothness of smoke, or ash color. The seven-day flush period had the highest “bad” rating (21.1%), and the 0-day flush had the highest “great” rating (16.7%). Most panelists rated the flavor of the samples as “okay” or “good.” The ten-day flush had the highest “okay” ratings at 48.6%, and the 0-day flush had the highest “good” rating at 47.2%.

The terpene profile, as tested by a third-party laboratory, indicated earthy to spicy flavors for all flush treatments. Most panelists rated the samples as either “earthy” or “sweet.” Sweet was chosen as the predominant flavor by 38.9% of panelists for the ten, and seven-day treatments and 32% of panelists selected sweet as the dominant flavor for the zero-day treatment. Panelists selected earthy most frequently (32.4%) as the dominant flavor for the 14-day flush.

In this trial, Rx Green Technologies evaluated the effects of the flushing period on yield, potency, terpenes, mineral content, and taste characteristics of cannabis flower. Overall, the length of the flushing period did not impact the yield, potency, terpenes, or taste characteristics of Cannabis flower. Taste test results indicated a trend toward improved flavor and smoke quality with the zero-day flush. While there were no significant differences in nutrient content, there was a trend toward increased iron, and zinc in flower flushed for 14 days. The results of this trial indicate that there is no benefit to flushing Cannabis flower for improved taste or consumer experience.

Click here to read the complete study. 

For more information:
RX Green Technologies