In the world of rosin presses, perhaps the most important elements in the extraction process are your heat plates (also referred to as heat platens or simply platens). Heat plates for a rosin press come in a wide variety of sizes and shapes, but they are typically only made with a few different common grades of stainless steel or aluminum. Depending on who you talk to, you will get a different story and many theories currently circulate as to which is better. In this article, we’re going to weigh the pros and cons of the most popular stainless steel and aluminum alloys that are used in rosin press heat plates, as well as discuss other implications with using those metals concerning consumable, concentrated cannabis products.
Virtually all metals come in many different grades, which are determined based on their purity as well as what other compounds (often other metals) they are mixed with. These other metals are called alloys. The metallurgy of each different alloyed metal will offer unique qualities intended for particular applications, so choosing the correct heat plate metal for your rosin press is critical to get the most out of your production. Perhaps the most common grade of aluminum used for rosin press heat plates is 6061 which is treated with magnesium and silicon, otherwise known as aircraft grade aluminum. For stainless steel, some of the most popular alloys are 304 or 316 which contain nickel and chromium, both which have unique properties suited for a wide variety of tasks. Given the amount of metal used in a standard set of rosin press heat plates, cost is typically not much of a consideration.
There are two primary factors you should consider when it comes to selecting which metal you want to use with your heat plates on a rosin press, and in priority they are:
Image Credit: PureTemp.com
The thermal conductivity of your heat plates is arguably the most important factor to consider when selecting which heat plate material you intend to use to press rosin. Even heat distribution + pressure + cannabis material = rosin. Thermal conductivity is typically measured in watts per meter-kelvin, or expressed as ((W/(m. K)). It is also expressed via Fahrenheit in a similar formula, but without getting overly technical, we’ll leave you with the following eloquent explanation. Via Engineering Tool Box, “Thermal Conductivity - k - is the quantity of heat transmitted due to a unit temperature gradient, in unit time under steady conditions in a direction normal to a surface of the unit area.” Each metal has its own k value, with a higher number equating to better, more efficient heat distribution.
Surprisingly, pure aluminum comes in at a k value between 200 to 249, and stainless steel offers a k value of 12 to 45. This means that most grades of stainless steel only offers 6% to 18% of the thermal conductivity that aluminum does. While heating elements deserve their entire own article which we’ll tackle down the road, what you need to know is that stainless steel of virtually all grades, as well as plain carbon steel, are poor conductors of heat across the board, whereas aluminum is considered one of the best. Other notable metals that conduct heat well are gold (k = 318), pure copper (k = 389), or even better, pure silver (k = 407). If someone wants to make a set of pure silver heat plates for us to play with at the PurePressure lab, we wouldn’t mind testing them!
Secondly, durability is the other key factor to consider when selecting a heat plate metal. Metal durability in science is often expressed on the Brinell scale, or, less commonly, the Mohs scale. For our purposes, we believe the Brinell scale is more useful, which is represented as BN. The higher the number, the harder the metal. In this instance, stainless steel is clearly the harder metal, where 316 stainless steel has a BN rating of 217 and 6061 aluminum has a BN rating of 95. Aluminum is often about 57% softer and is more prone to scratching depending on the application and the thickness of the aluminum itself. Unless your heat plates are very thin, there is virtually no risk of warping with either metal. Another factor in durability considerations is corrosion resistance; both aluminum and stainless steel tend to be quite corrosion resistant thankfully. When it comes to rosin press heat plates, extra hardness does not necessarily equate to a longer lifespan however, due to the softness of the materials being pressed. If you were stamping metal instead, stainless steel would likely be your metal of choice.
Given that rosin is made most often with cannabis flowers, kief (trichome heads), or bubble hash, all of which are very soft, you are unlikely to wear out stainless steel or aluminum heat plates even with continuous use. If your heat plates are uneven, contoured, or aren’t precision machined from thick stock material they could wear out quickly regardless of what metal was used to produce them. Furthermore, most rosin is pressed in a polyester, nylon, or silk filter bag between sheets of parchment, which virtually eliminates potential scratching. In some instances woven stainless steel filter bags are used, although far less commonly. These bags could potentially scratch aluminum if pressed without parchment or with thin, low quality parchment paper.
Why Thermal Conductivity Matters Most
When you compare the different qualities that stainless steel and aluminum have, it’s worth understanding why thermal conductivity should be your keystone measure here. Rosin press heat plate thermal conductivity is important because high thermal conductivity aides in the transfer of heat from the heat plates to the material being pressed. Combined with pressure, that heat is used to liquefy your oils and lower their viscosity so they may freely flow from the rosin filtration bag. When the heat is able to transfer efficiently you will liquefy the oils in less time and the oil will raise in temperature uniformly instead of having hot and cold spots. This means that with aluminum, you have greater process control and ultimately a better shot at higher, more consistent yields with your rosin press. The more quickly your oil escapes the heat, the higher the terpene preservation tends to be, which can often increases the quality of rosin tremendously.
Food Grade Designation: Does it Matter?
A commonly touted advantage of stainless steel is that it qualifies as “food grade”, which is determined by the FDA in the United States as a set of guidelines that metals must have in order to safely make contact with food. In fact, many varieties of both aluminum and stainless steel qualify as food grade, along with many other materials that are deemed by the FDA as “Effective Food Contact Substances”. The catch here is that when rosin is pressed between parchment paper, it automatically becomes qualified as a food grade production. This is in reference to the gelatin in parchment paper, hence the food grade qualification. Unfortunately, the FDA has scant information available on the subject and nearly all parchment paper is sold as food grade, whether it is bleached or unbleached. Another issue that is occasionally brought up is the safety of aluminum itself as a food contact metal, which has been demonstrated by the Agency for Toxic Substances & Disease Registry as a safe metal. Both stainless steel and aluminum are ubiquitous in the food industry and aluminum especially is prized for its even heating properties for a wide range of cooking applications.
Conclusion: Stainless Steel vs. Aluminum for Rosin Press Heat Plates
Suffice to say, this is a topic where it’s a little too easy to go down the rabbit hole on material sciences, tensile strengths, and some very complex topics. For the utility of our readers, we feel that the important takeaway is that, above all else, aluminum offers vastly superior thermal conductivity for pressing rosin despite being a softer metal. Poor or uneven heating conductivity can result in low yields and inconsistent rosin, which isn’t what you want when you’re trying to produce the best solvent-less rosin around. The type of metal used in your heat plate is certainly not the only factor involved in heat distribution, but it is a major one, and heating element design deserves its own discussion. It’s worth mentioning that while there are plenty of people who successfully use stainless steel heat plates, they very well could be getting better results with aluminum. As mentioned before, thermal conductivity can have a significant impact on the consistency, quality, and terpene preservation of your rosin.
In conclusion, the engineering staff here at PurePressure strongly believes based on comparing and contrasting the physical properties of stainless steel vs. aluminum that for rosin, you should demand aluminum heat plates in your equipment. Whether you’re using your own at home press or our industry leading Pikes Peak rosin press, we absolutely recommend high quality aluminum heat plates for the best results.
- Very durable, high tensile strength, but offers very poor thermal conductivity
- Very high thermal conductivity, softer, prone to scratching