The Physics Behind Rosin: Heat & Pressure
At PurePressure, we believe there is a rather large misconception in the rosin community that increased capacity by larger plates and a huge tonnage is an effective way to ensure higher yields. This is not necessarily the case. The aromatic terpenes and bright yellow color most people love in rosin is best achieved in small batches where the material spends minimal time in contact with heat. Color is mostly affected by the age and quality of the material. However, if too much pressure is applied there is a high probability that extra plant matter will find its way into the rosin and can reduce the quality of the final product. Rosin needs precise heat distribution to ensure proper flow, and it needs to have the proper amount of pressure at the bag. This is best achieved with the proper implementation of a basic equation: Pressure(PSI)= Force(LBF) / Area(IN^2) and by consistent heat application. When deciding what rosin press to use you should consider the following: plates (are they rectangular or square?), heat distribution (is it even?), pressure (what is optimal for the material you are pressing?). We will consider all of these factors in detail below.
To start, the plates of a rosin press should always be rectangular (ideally long and narrow, as well). There are two key reasons for this.
1) Rectangular plates maximize the perimeter to area ratio. Your bag of material will be squished between two plates effectively eliminating the top and bottom areas as possible escape routes. By dividing the perimeter of the bag by the area of the bag we are able to compare any bag size with a single metric. This metric or ratio gives us the perimeter of a bag per 1 square inch of area. In the example below you can see our 2” x 9” bag has 1.333” of perimeter per square inch of area. This large perimeter is important so that the rosin has the largest exit area. A waveform seam would theoretically be best for rosin because it would maximize perimeter. However, the rosin would get trapped in the seams and end up decreasing yield. The three equations that are important to think about are:
Area (A) = L1 x L2
Perimeter (P) = 2L1 + 2L2
Perimeter/Area = P / A (For best results maximize this number)
Exactly how a rectangular shape maximizes the perimeter/area ratio is easiest to see if we work out the math. I’ll take two common bag sizes just to make it easier to see.
2” x 9” bag (PurePressure Bag)
L1 = 9”, L2 = 1.8” (actual bag dimensions)
Perimeter = 2*(9) + 2*(1.8) = 21.6”
Area = 1.8 x 9 = 16.2 in^2
Perimeter/Area = 21.6/16.2 = 1.333
6” x 6” bag (Square Competitor's Bag)
L1 = 6”, L2 = 6”
Perimeter = 2(6) + 2(6) = 24”
Area = 6 x 6 = 36 in^2
Perimeter/Area = 24/36 = 0.667
As you can see by these two commonly used bag sizes 1.333 > 0.667. In this example, the rectangular PurePressure bag has twice as much perimeter/area compared to the competitors square bags.
2) The distance from the center of the bag to the edge of the bag should also be minimized. L2/2 is the maximum distance the rosin will need to travel to exit the bag. Larger distances (L2/2) increase the amount of time the material is in contact with heat and is the largest contributing factor to terpene degradation. A larger L2/2 also increases the likelihood of oils getting trapped inside the bag which can dramatically decrease yields. Reference Figure 1.
When making rosin it is very important to have even heat distribution. Heat lowers the viscosity of rosin by melting the trichome heads and stalks. Applied pressure mobilizes the less viscous cannabinoids and forces them out of the filter bag. Altering the temperature of the heat plates is what changes the oil’s texture and is primarily how you manipulate rosin into shatter, budder, wax and other consistencies. Even minor variances in temperature across the surface of the heat plate can produce mixed textures and small texture flaws which would be avoided on a more consistent surface.
Even heat is also essential for maximum rosin flow. Think of it this way. If there is a lot of traffic on the highway moving at a consistent speed there are no problems. If one car slows down even a little a traffic jam forms. This is the same for temperature discrepancies in rosin. Introducing cold spots will cause the rate of flow to slow down and will increase press time causing terpene degradation. It is possible that the rosin will be slowed to a stand still and will not make it out of the bag at all, which will decrease yields. In the worst case scenario, the pressure of the liquid trying to escape will build up until it exceeds the strength of the rosin bag, resulting in a bag blow-out.
We performed measurements on a variety of heat plates using a thermocouple, thermal paste and kapton tape. One of the commercial presses we measured had a 90℉ variance in temperature. This is the equivalent of a sudden stop from 60 mph. It’s a wreck. One thing that attributes to this huge differential is heating coil placement. Some rosin presses use U-shaped coils. This is not a good idea. With this heat coil placement the center is cold. By the time the center is hot enough to mobilize the rosin the area directly over the heating element is much hotter and will likely burn the material. As the rosin reaches the edge of the plate it is cooled, which slows down the flow and often decreases yield. These heat plates will produce significant flaws in consistency. PurePressure’s heat coil placement ensures the most consistent heat distribution over the entire surface of the plate ensuring replicable texture and consistent flow.
Note: infrared thermometers do not work on shiny surfaces such as our machined aluminum heat plates because their emissivity (reflectiveness) will produce a dramatically lower reading.
Probably the most misunderstood part of making Rosin is the concept of pressure. There are many things that affect the pressure required for optimal results: material type (bubble, kief, or flower), humidity, quality of grow, cure method, and age of material. For each set of conditions there will be often be an ideal "sweet spot" for optimal pressure.
The graph below shows how the sweet spot (area between the dotted lines) we've come up with changes for bubble, kief, and hash.
As you can see there is a point at which, although you may still be increasing yield, you may actually be pushing fats, lipids and chlorophyll into your rosin, potentially decreasing quality. This is particularly problematic if you are making flower rosin where more inert, organic material is possible to be over-pressed.
Based on extensive pressing and anecdotal conversations with hundreds of our customers, we feel that we've honed in on some these pressure guidelines that will help most users achieve excellent results with their rosin press. It is currently our belief that the optimal pressure range for pressing rosin is between 300 and 1000 psi, at the bag. Flower will be on the upper end at 600-1000 psi and kief or hash will be on the lower end between 300 and 800 psi. The plate size does NOT factor into these numbers. If you have a 20 ton press and press a 2x9 bag you will get 2500 psi at the bag. With a 2x3 bag you will get 7500 psi at the bag. These PSIs may marginally increase yield but it is likely that the increased yield is at the expense of the purest quality possible.
Given this, we completely accept the fact that there are many people who would disagree with us here and produce great rosin on higher tonnage presses. We believe that has a lot more to do with the quality of their material however than any excess pressure being applied.
So how is pressure achieved and how do you calculate pressure at the bag? Please refer to figure 4 below:
On a pneumatic press pressure is generated by compressed air which enters the machine and is distributed over the area of a piston. Pressure = Force / Area so Force = Pressure x Area. The cylinder on the Pikes Peak Press is 82.3 in^2. With 120 psi of air entering the machine we calculate 82.3 in^2 x 120 psi = 9,876 LBF. Since 2,000 LBFs equals 1 ton we can see that the Pikes Peak pneumatic press generates approximately 5 tons of force. This is the force at the plates. However, what we really care about is the force at the bag.
We will now calculate the pressure at the bag using the equation Pressure = Force / Area, where area is the size of the bag. For example, the area of a 2” x 9” bag is 1.8” x 9” = 16.2 in^2. (1.8” is the true measurement inside the seam). If we plug that number in we get 10,000 / 16.2 = 617 psi at the bag. Now let’s run this calculation for our 2” x 3” bags. 1.8” x 3” = 5.4 in^2. 10,000 / 5.4 = 1,851 psi at the bag. As you can see the smaller the bag, the more pressure you will get. Think of a nail. A nail tip exerts a large amount of pressure on whatever it is traveling into because it has a tiny area. If you hit a hammer with the same force but drive the head of the nail into the wood rather than the tip it will barely dent the surface. This is because it has a larger surface area. When creating recipes for a specific batch of material, you will want to know the pressure at the bag that produces the highest quality and yield. You will be able to scale your recipe up or down in size with replicable results by maintaining a constant bag pressure. For example if we create a recipe that works well in a 2” x 3” bag and we want to scale up to a 2” x 9” bag we will increase the air pressure entering the machine, compensating for the larger bag area and maintaining a constant bag pressure.
PurePressure is completely biased when it comes to our passion for rosin. We love the concentrate for its ability to reveal the growing process, for its lack of adulterants, and because the process of making it is beautifully simple yet artful. Making rosin takes consistency and finesse. It will never be BHO or CO2. This is why it gets a higher price point and why it is special. It is not my intention to say that it is impossible to get good results making rosin with high tonnage and large plates. What I am saying is high tonnage and large plates should not be the emphasis. PurePressure has researched each aspect of the process to dial in what makes truly exceptional rosin. We have designed rectangular heat plates that maximize yield while preserving terpenes. We have dialed in a temperature regulation system that consistently distributes heat within only 1 degree discrepancy and we have found a way to apply and control pressure maximizing quantity and quality. What PurePressue has found, and truly believes, is that the key to rosin is finesse not brute strength.