“Medusa Fast Crash” vs. Super-Saturation Precipitation
Understanding the Real Cause of Sudden THCa Crashes
If you’ve worked in cannabis hydrocarbon extraction since at least 2020, you’ve almost certainly heard the terms “Medusa Stones” or “Medusa fast crash.” They’re usually shared as horror stories: beautiful, clear THCa diamonds suddenly turning opaque white, or extracted oil violently precipitating THCa either inside the system or immediately after pouring.
In extreme cases, operators describe rapid solvent off-gassing occurring simultaneously with precipitation, creating a dangerously aggressive reaction. Attempts to seal a vessel during this window can result in rapid pressure buildup followed by sudden expulsion of material — often described as a “volcano.”
Although these events are often grouped under the same nickname, they are not the same phenomenon.
Understanding the difference matters — not just for product quality, but for safety, reproducibility, and accountability.
The Industry Divide: User Error or Contaminated Solvent?
This topic remains controversial because opinions in the industry tend to be black or white, never gray.
Depending on who you ask:
• Fast crashes are purely user error, caused by poor control of saturation and temperature or
• They’re the result of contaminated LPG solvents, particularly butane There is rarely a middle ground.
The reason is simple: operators can intentionally induce rapid THCa precipitation by overshooting supersaturation. Because this behavior is controllable, many dismiss contamination as a factor altogether.
The reality is that both sides are correct — depending on the season.
The Seasonal Variable Most People Miss
In practice, 95–100% of fast-crash events are user error during the summer months. During winter, however, that percentage drops dramatically.
Why?
Because winter fundamentally changes how butane is produced, stored, and distributed.
During colder months, butane demand increases sharply due to its use as a gasoline additive. Its high volatility improves cold-start performance by vaporizing easily at low temperatures. To meet this demand, refineries are forced to draw deeper from storage tanks than they normally would.
And that’s where problems begin.
How Butane Storage Allows Contaminants to Concentrate
Instrument-grade butane (≥99.5%) is typically stored in large bulk tanks. While these tanks are not perfectly static systems, low turnover and long storage times allow impurities to concentrate — particularly toward the bottom “heel” of the tank.
Over time, compounds with differing density, polarity, and intermolecular behavior can preferentially accumulate in lower portions of the vessel. During periods of low demand (summer), refineries typically pull from the cleaner upper portion of the tank. During high demand winter months, they are often forced to siphon lower.
This behavior is common in bulk liquid storage systems and becomes more pronounced under sustained demand pressure.
A Simplified Stratification Hierarchy in Low-Turnover Butane Storage
In large, low-turnover storage tanks, impurities can accumulate over time according to differences in physical and chemical properties. While real-world tanks are subject to mixing and temperature changes, prolonged storage with minimal agitation allows preferential concentration, especially near the tank heel.
From top to bottom, a simplified hierarchy may resemble:
1. n-Butane
The primary solvent phase; lowest density and least polar.
2. Light “Heavy Ends” (e.g., n-Pentane)
Slightly higher-boiling hydrocarbons that remain miscible and are generally benign with respect to fast-crash behavior.
3. Amines (e.g., Methylamine)
More polar and denser than butane; tend to concentrate in lower portions of the liquid phase under low-turnover conditions.
4. Heavier Hydrocarbons (Hexane, Heptane)
Increase boiling point and viscosity; not associated with aggressive evaporation.
5. Aromatic Trace Contaminants (e.g., Benzene)
Typically present at very low concentrations; not causative of fast-crash events.
6. Ammonia (Condition-Dependent)
Can dissolve into liquid phases or partition into vapor space depending on temperature and saturation state.
7. Ammoniated Methanol
The densest and most polar fraction; preferentially accumulates in the tank heel and represents the highest risk for winter fast-crash behavior.
Which Contaminants Actually Matter?
Not all impurities are problematic.
Heavier hydrocarbons such as pentane, hexane, and heptane raise boiling points when mixed with butane and can largely be excluded as causes of aggressive evaporation or rapid precipitation.
The contaminants that matter most are:
• Methylamine
• Ammonia
• Ammoniated methanol
These compounds fundamentally change both solvent behavior and THCa chemistry.
Why Ammonia and Methylamine Change Solvent Behavior
When ammonia or methylamine is present in butane, the mixture can exhibit non-ideal vapor pressure behavior, including minimum-boiling azeotropic effects.
In practical terms:
• The mixture behaves as though it has a lower effective boiling point • Off-gassing becomes more aggressive
• Evaporative cooling continues beyond what pure butane would normally allow
Pure n-butane boils at ~31–32°F. When evaporating in an open container, the vessel cools until it reaches this temperature, at which point boiling slows dramatically.
But butane contaminated with ammonia or methylamine does not stop at 32°F. It continues to off-gas, driving temperatures even lower.
This creates a dangerous feedback loop:
1. Aggressive evaporation
2. Rapid temperature drop
3. Increased THCa supersaturation
4. Sudden precipitation
And that’s only half the story.
The Chemical Interaction with THCa
Ammonia and methylamine don’t just affect solvent behavior — they interact directly with THCa.
THCa is an acid. Ammonia and methylamine are bases.
When they come into contact, acid–base neutralization can occur, forming amine salts of THCa, such as ammonium tetrahydrocannabinolate. These salts exhibit very low solubility in butane and tend to precipitate rapidly — sometimes before the solvent has even exited the material column.
This mechanism is fundamentally different from supersaturation-driven crystallization.
The Role of Ammoniated Methanol
Ammoniated methanol is a strong indicator that solvent supply chains are being pushed to their limits.
In winter:
• Cold methanol holds significantly more dissolved ammonia
• The ammonia remains bound until a stronger chemical partner is introduced • THCa, being acidic, pulls ammonia away from methanol almost instantly This results in immediate salt formation and fast-crash behavior.
In summer:
• Ammonia solubility in methanol decreases
• Most ammonia migrates to the vapor headspace
• Remaining methanol acts primarily as a crystallization modifier
This produces distinct THCa morphologies — bars, needles, or “urchin” growth — rather than violent crashes.
It’s worth emphasizing how uncommon this scenario is. To date, we have only observed true methanol-driven THCa morphology once in the industry, and it occurred during the summer months. Since that event, reported incidents have overwhelmingly involved winter fast-crash behavior, consistent with ammonia- or amine-driven mechanisms rather than methanol-modified crystallization.
Why 2020 Matters
The first widespread reports of “Medusa” behavior appeared in summer 2020, during the height of the COVID-19 pandemic.
During this period:
• Refinery utilization dropped to historic lows
• Maintenance and water-wash cycles were postponed
• Fractionation efficiency declined
• Storage tanks were drawn down to their heels due to supply disruptions The result was increased methanol and amine carryover into butane streams.
Notably, those early events produced methanol-driven morphology changes, not winter-style fast crashes — further supporting the seasonal contamination model.
The Melt-Point Test: User Error or Contamination?
This is the most practical diagnostic tool available.
When THCa precipitates rapidly, measure its melting point:
• ~158°F → Likely pure THCa
→ Supersaturation or process-control issue
• ~100°F or lower → Likely amine-salt contamination
→ Solvent quality issue
Amine salts trap residual solvent and ammonia within the solid matrix, dramatically lowering the apparent melting point.
This simple test can immediately distinguish operator error from contaminated solvent.
Final Thoughts
Fast THCa crashes are not always caused by poor technique.
In summer, they almost always are.
In winter, solvent quality becomes a critical variable.
Understanding seasonal refinery behavior, contaminant chemistry, and simple diagnostic tools allows operators to move past blame and toward real solutions.
If you want consistent crystallization outcomes year-round, controlling saturation isn’t enough — you must understand your solvent supply chain.
