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Standard Operating Procedure: Cannabis Extract Winterization
1. Purpose
This SOP defines the procedure for winterization (dewaxing) of crude cannabis extract using cold ethanol to remove fats, lipids, and waxes. Winterization improves clarity, flavor, and downstream processability of the extract for distillation or further refinement.
2. Scope
Applies to all winterization operations performed on BHO crude, CO2 crude, or ethanol crude extract. This SOP covers dissolution, cold soaking, filtration, and solvent recovery.
3. Equipment & Materials
| Item | Specification | Notes |
|---|---|---|
| Food-grade ethanol (190+ proof) | 95%+ purity, USP grade | 200 proof preferred for maximum lipid precipitation |
| Freezer or chest freezer | -20C (-4F) minimum; -40C (-40F) preferred | -40C removes more waxes; -20C adequate for most operations |
| Glass or stainless mixing vessel | Appropriate for batch size | Must be solvent-compatible. No plastic. |
| Buchner funnel + vacuum flask | Porcelain or stainless, sized to batch | Ensure vacuum flask rated for ethanol vapors |
| Filter paper | Qualitative, 20-25 micron | Whatman #4 or equivalent. Slower paper = cleaner product. |
| Vacuum pump | Oil-sealed or diaphragm | Diaphragm preferred for solvent-safe operation |
| Rotary evaporator or recovery unit | Sized to batch volume | For ethanol recovery after filtration |
| Thermometer / IR thermometer | -50C to +50C range | Verify freezer and solution temp before filtering |
| PPE: nitrile gloves, safety glasses, lab coat | Chemical-resistant | Ethanol is flammable. No open flames. |
4. Safety Requirements
- Ensure adequate ventilation (minimum 12 air changes per hour in processing area)
- Keep a Class B fire extinguisher within 10 feet of the workstation
- Wear nitrile gloves (latex degrades in ethanol), safety glasses, and lab coat
- No open flames, sparks, or non-intrinsically safe electronics in the work area
- Ground all metal vessels and funnels to prevent static discharge
5. Procedure
1 Dissolve Crude in Ethanol
Combine crude extract with 190+ proof ethanol at a ratio of 10:1 ethanol to crude by volume (e.g., 1L ethanol per 100g crude). Stir until fully dissolved. The solution should be uniform with no visible chunks or separation.
| Parameter | Target | Acceptable Range |
|---|---|---|
| Ethanol:Crude ratio | 10:1 (v/w) | 8:1 to 15:1 |
| Ethanol proof | 190+ (95%+) | Minimum 190 proof |
| Dissolution temperature | Room temp (20-25C) | Do not heat above 40C |
| Stir time | 5-10 minutes | Until fully dissolved |
2 Cold Soak
Place the sealed vessel in the freezer. Soak for a minimum of 24 hours at -20C or 12 hours at -40C. The cold temperature causes fats, lipids, and waxes to precipitate out of solution and form visible sediment or a cloudy suspension.
| Parameter | Target | Acceptable Range |
|---|---|---|
| Soak temperature | -40C (-40F) | -20C to -80C |
| Soak duration at -40C | 12-24 hours | Minimum 12 hours |
| Soak duration at -20C | 24-48 hours | Minimum 24 hours |
| Vessel type | Glass or stainless, sealed | Must be solvent-compatible |
3 Filtration
Filter the cold solution through the Buchner funnel with 20-25 micron filter paper under vacuum. Work quickly. The solution must stay cold during filtration. If the solution warms above -10C, precipitated waxes begin redissolving and pass through the filter.
| Parameter | Target | Acceptable Range |
|---|---|---|
| Solution temp at filtration | Below -20C | Must remain below -10C |
| Filter paper | 20-25 micron (Whatman #4) | 10-25 micron |
| Vacuum pressure | 15-20 inHg | Do not exceed 25 inHg |
| Filtration time | 10-30 minutes per batch | Replace filter if flow stops |
Tips for efficient filtration:
- Pre-chill the Buchner funnel and flask in the freezer for 30 minutes before use
- Use a coffee filter or coarse pre-filter above the primary filter to catch large wax particles
- If filtration slows, replace the filter paper. Do not increase vacuum excessively.
- For large batches, filter in portions rather than pouring all solution at once
4 Optional: Second Filtration Pass
For higher-purity product (distillation feedstock), return the filtrate to the freezer for an additional 4-8 hours, then filter again through a finer filter (10-15 micron). This removes residual micro-waxes that passed the first filter.
5 Solvent Recovery
Transfer the winterized filtrate to the rotary evaporator or solvent recovery unit. Recover ethanol at 40-50C bath temperature under vacuum (100-150 mbar). Continue until no more ethanol condenses and the extract has reached the desired consistency.
| Parameter | Target | Acceptable Range |
|---|---|---|
| Bath temperature | 40C (104F) | 35-50C |
| Vacuum level | 100-150 mbar | 50-200 mbar |
| Rotation speed (rotovap) | 80-120 RPM | Adjust to prevent bumping |
| Target residual ethanol | <5000 ppm | Per state/jurisdiction requirement |
6 Final Product Assessment
Weigh the final winterized extract. Calculate yield based on starting crude weight. Inspect for clarity, color, and consistency.
| Parameter | Expected Range | Notes |
|---|---|---|
| Winterization yield | 70-85% of crude weight | 15-30% removed as fats/waxes |
| Color | Lighter than crude input | Golden to amber for BHO/CO2 crude |
| Clarity | Clear to slightly hazy | Cloudy = incomplete winterization |
| Consistency | Thick oil to sap | Varies by starting material |
6. Troubleshooting
| Problem | Likely Cause | Corrective Action |
|---|---|---|
| No visible precipitation after soak | Freezer temp too warm, or crude already low in fats | Verify freezer temp with thermometer. Extend soak to 48h. Try -40C if using -20C. |
| Filtrate still cloudy | Solution warmed during filtration | Re-chill and re-filter. Pre-chill all filtration equipment. |
| Filter clogs immediately | Too much precipitate or filter too fine | Use coarse pre-filter. Filter in smaller portions. |
| Low yield (<65%) | Excessive soak time at very low temps, or crude was high in fats | Normal for high-fat crude (CO2, warm ethanol). Verify no product left on filter cake. |
| Final product smells of ethanol | Incomplete solvent recovery | Continue rotovap at 45C/100 mbar until no condensation. Check for leaks in vacuum system. |
| Waxes return after storage | Product stored cold, residual waxes crystallize | This indicates incomplete winterization. Re-winterize at lower temp. |
7. Batch Record
| Batch Number: | Date: | ||
| Operator: | Reviewer: |
| Record Item | Value |
|---|---|
| Crude input weight (g) | |
| Crude source/type | |
| Ethanol volume (mL) | |
| Ethanol:Crude ratio | |
| Freezer temperature (C) | |
| Soak start time | |
| Soak end time | |
| Total soak duration (hours) | |
| Solution temp at filtration start | |
| Solution temp at filtration end | |
| Filter type/size | |
| Second pass? (Y/N) | |
| Rotovap bath temp (C) | |
| Rotovap vacuum (mbar) | |
| Ethanol recovered (mL) | |
| Final winterized extract weight (g) | |
| Yield (%) | |
| Visual assessment (color/clarity) | |
| Residual solvent test result (ppm) |
8. QC Checkpoint Summary
| ☐ | Checkpoint | Criteria | Pass/Fail | Initials |
|---|---|---|---|---|
| ☐ | 1. Dissolution | Solution fully dissolved, no visible chunks | ||
| ☐ | 2. Cold soak | Visible precipitation after soak period | ||
| ☐ | 3. Filtration | Filtrate clearer than input; filter cake contains wax | ||
| ☐ | 4. Solvent recovery | No ethanol odor; residual below 5000 ppm | ||
| ☐ | 5. Final assessment | Yield 70-85%; clear to slight haze; golden-amber color |
9. Revision History
| Version | Date | Author | Changes |
|---|---|---|---|
| 1.0 | Initial release |