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Modern Methods Pt. 2

Modern Methods for Rosin Extraction Part 2: Techniques

Part 1 of this document offered background information on rosin.  Part 2 will focus on how to actually extract it. {covers topics related to rosin extraction.}  

Rosin is a cannabis concentrate obtained by exposing a starting material (flower, kief,  hash, fresh frozen hash, etc.) to a combination of heat and pressure. The critical steps of the extraction procedure are as follows: the starting material must be placed in a filter that keeps all the unwanted plant matter contained during pressing but allows the expressed oils (i.e. the rosin) to pass through.  A piece of parchment paper is placed around the filter so that when the little packet is put on a heat press and squeezed, the oils oozing out of the pouch never come into direct contact with the heated elements.

The 5 Variables in Rosin Pressing

Rosin pressing is more of an art than a simple process that can be repeated over and over in exactly the same way.  Mastering this art entails understanding the five crucial variables of the procedure (starting material, time, heat, pressure, and filter size) and the ways that they relate to each other.  Being able to bring these variables into harmony is the key to pressing good rosin. Failing to properly account for these factors, on the other hand, can have serious negative effects on rosin quality, including discoloration and terpene evaporation.  For this reason, we recommend learning about these five variables before diving into the steps of the extraction procedure.

Starting material: The quality of a rosin sample is highly dependent on the quality of the starting material from which that rosin was extracted.  In other words, beginning with high quality starting material is crucial to obtaining high quality rosin. Input quality, which is discussed in greater detail in Part 1, may vary for several reasons.  The freshness of the starting material has a significant impact on its quality, as do the conditions under which the plant was grown. When working with flower, it’s important to ensure that its humidity level remains relatively high (at roughly 60%).  Flower that gets too dry is subject to preventable terpene evaporation and other forms of degradation, such as trichome heads taking on an amber tinge.

All shortcomings on the input side will be reflected in the final product, which is why it’s so important to select the right starting material.

Time: Three of the five variables are so closely interrelated that it’s worth explicitly noting the connection between them.  These are A) the heat and B) the pressure applied during the extraction process and C) that process’s duration.  There is no “perfect amount of time” for pressing rosin, because the ideal duration depends on the heat and pressure levels.  The only way to consistently press high quality rosin is to learn how to maintain a balance between these three variables. If one is adjusted, one or both of the others must be counter-adjusted accordingly.  For example, when experienced rosin processors increase the temperature in the heat plates, they compensate by pressing for a shorter amount of time and possibly also by reducing the pressure.

Heat: Ideal heat levels vary based on starting material, but there are a few best practices guidelines that apply regardless of temperature.  First and foremost, the heat applied to starting material should be consistent. Second, the heated platens should have an even heat signature and be free of “hot spots”.  If these conditions are not met, it may be impossible to ensure rosin quality from one pressing to the next.

Finally, while it’s true that there is no “perfect” heat setting, starting materials should not be exposed to excessive heat as this can lead to unnecessary THCA decarboxylation and terpene evaporation, two pitfalls described in Part 1.

Pressure: When too much pressure is applied to the starting material, or pressure is applied too quickly, the filter may give way.  Avoiding such events--called blowouts because they allow undesired plant matter to escape containment and mix with the rosin--is a primary consideration when choosing pressure settings.

To avoid blowouts, it’s important to choose both the right amount of pressure and the right rate of increase, which determines how quickly the amount of force that’s being applied climbs from 0 PSI up to the selected pressure level.  Choosing the right rate of increase is all the more important when the starting material is very oil-rich. This is because of the physical limitations of filters: there is a maximum amount of oil that can pass through them in a given amount of time, and trying to force more oil through a filter than it’s able to permit will result in a blowout.  

Another important consideration: over the course of several seconds, the press’s heat and force cause the compressed “puck” of starting material to melt and become thinner.  In order to keep the amount of pressure on the puck from changing, the two plates must move slightly closer together, by a distance equal to the thickness that the puck lost when it melted.  Failure of the press to automatically adjust leads to a decrease in pressure, and because heat and pressure are interrelated, this drop causes a reduction in heat transfer as well. As stated above, pressing with inconsistent temperatures can lead to variations in rosin quality.  

Some devices--manual hydraulic presses, for instance--don’t allow users to easily adjust the distance between the plates once pressure is being applied.  However, pneumatic presses automatically adjust the position of their plates based on changes in a puck’s thickness. This ensures that the pressure applied (and therefore the heat transfer) is consistent.  

Filter size: A couple of questions must be considered when choosing a filter.  First off, how much starting material is to be processed in a single pressing?  Bigger filters hold more starting material, of course, but bigger isn’t always better.  Attempts to press too much may cause a portion of the oils to undergo heat-related degradation because they must travel a longer path to exit the puck, which means they’re exposed to heat for more time.  

Another factor that should be considered in choosing a filter is starting material.  Different materials require different mesh sizes. For example, a much larger mesh size (i.e. a higher micron count) is appropriate when pressing flower than when pressing kief, because kief is made up mostly of small particulate matter that would easily pass through a large filter.   

Other Key Topics

Several of the ideas introduced in the “5 variables” section deserve further explanation.

Avoiding Blowouts: Blowouts are not completely catastrophic; the resulting mix of rosin and unwanted plant matter can be cleaned up in a second pressing, which yields an extract of only slightly reduced quality.  Blowouts can also happen to anyone; they’re not 100% preventable. However, certain precautions, when taken, usually prove effective in preventing these events.

One of the main causes of blowouts is inserting too much starting material into a filter.  Overpacking can lead to a situation in which, under the pressure of the plates, the material is pushed outward with a force strong enough to make the filter unfold or tear, or to break the string that’s holding it in the shape of a folded pouch.  

Blowouts are more likely to occur when filters are packed freehand, because the contents of hand-packed filters may not be uniformly distributed.  Between a pair of heat plates, the loosely packed areas experience less pressure than they’re intended to while the more densely packed areas experience more, and it’s these areas that are at risk of blowing out.  Many rosin processors use pre-press moulds to avoid blowouts related to the uneven distribution of starting material.

Matching the plate, mould and filter:  In order to maximize the quality and quantity of rosin obtained in a single pressing, it’s important to use plates, a mould, and a filter of matching sizes.  This is the case for several reasons.

Using a mould that’s been tailored to the dimensions of the filter not only reduces the risk of blowouts, it also minimizes the amount of open space in the middle of the filter and along its seams.  This helps to increase the amount of starting material that can be processed in a single pressing without sacrificing quality.

It’s best to use a filter whose edges sit just within the edges of the plates, so that as rosin is pushed out of the edges of the filter, it escapes the hot environment between the plates almost immediately.  This spares the rosin from unnecessary terpene evaporation, THCA decarboxylation, and other forms of heat-related degradation.

Finally, by using smaller plates and a matching filter, experienced processors are able to obtain close to a full yield of rosin while maintaining a high level of quality due to the relatively short distance that oils must travel to escape the plates.  

Decarb and Terpene Evaporation: Though many people associate the term “evaporation” with boiling, the fact is that terpene evaporation even at room temperature.  Small scale terpene evaporation and THCA decarboxylation are an inevitable result of many concentrate extraction techniques, including rosin pressing.

The degradation that occurs when rosin is extracted properly does not appear to noticeably affect the quality of the concentrate, because it occurs at relatively low levels.  When pressing rosin, therefore, the objective is to avoid preventable decarb and terpene evaporation.