When processors start comparing various oilseed extraction methods and machines, they often ask us about the difference between expeller pressed versus cold pressed oil extraction. Unfortunately, this question doesn’t quite make sense — and here’s why.
Comparing expeller pressed versus cold pressed oil equipment
What processors are really asking about is the difference between hot pressing and cold pressing. The fact that people often associate the expeller press with hot pressing indicates some confusion between extraction equipment, like the Expeller, and the extraction process, like hot or cold pressing.
In the same way that people often use brand names like Xerox or Kleenex when referring to an entire product category, the Expeller trademark has become practically synonymous with a traditional screw press — which is typically associated with hot pressed oil. However, it’s important not to confuse the equipment with the extraction method, because an Expeller can be used for either hot pressing or cold pressing, depending on your full system process.
Ultimately, processors are trying to figure out the best extraction method for their facility, so they can select the right equipment to process oil efficiently. We’ll answer this burning question below by comparing hot and cold pressed extraction techniques. But first, we’ll offer some background about the expeller press to set the records straight so that you can ask the right questions about oilseed extraction.
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History of the Anderson Expeller Press
In 1900, Anderson International’s founder, Valerius D. Anderson, invented a new way to extract oil by developing the first continuous mechanical extractor. He patented this screw press under the trademark name, Expeller®, and Anderson International Corp. began selling them to oilseed processors around the world.
Initially, heat was not involved in the extraction process (at least, not beyond the frictional heat created by the mechanical screw press). Heat was added to the process later, in the 1910s, when Anderson discovered that cooking and drying the oilseed prior to extraction could make the pressing operation more efficient. This led to the development of Anderson’s line of extruders, cookers, dryers, and other specialized equipment that cooks and dries oilseed using steam heat and friction.
We’ll explain the benefits of adding heat to this process in the next section, but it’s important to remember that the Expeller press itself isn’t adding heat. Heat is added separately through dedicated upstream equipment like the Extruder, so trying to compare Expeller pressed versus cold pressed oil isn’t really an accurate comparison. It’s like comparing a Xerox to a color copy, when in fact, a Xerox machine can make color copies, too.
Now that you understand why the comparison is really between hot pressed and cold pressed oil, we can get to the answer.
What is hot pressing?
Hot pressing is the process of adding heat to cook and dry oilseeds prior to extraction. Although these steps are often conflated into one, cooking and drying are actually two separate processes that each serve a valuable purpose to prepare raw material for more efficient pressing downstream.
Cooking: In the first step, heat is applied to cook the oilseeds at a constant temperature and moisture —breaking down the material at the microscopic level using heat to release the oil trapped inside. This process traditionally used indirect steam heat vessels to maintain the oilseeds at a constant and elevated temperature, making the oil easier to extract.
Moisture is a critical element of the cooking process because it helps transfer heat more evenly and efficiently. At this point in the process, oilseeds typically have a moisture level between 10-12%. However, that moisture will make it harder for the press to operate downstream because it over-lubricates and even clogs the equipment. For this reason, it’s critical to remove the moisture after cooking by using — you guessed it — more heat.
Drying: After the cooking process, heat is added in a second step to dry the oilseeds — essentially removing excess moisture to prepare the material for more efficient pressing. Generally, material should be dried to less than 5% moisture content before heading to the press. The Anderson Expeller, for instance, processes most efficiently when material contains between 3-5% moisture.
Traditionally, oilseed processers used stacked batch cooking and drying vessels to generate steam heat for these added steps. Alternatively, the Anderson Dox™ (Dry Oilseed Extruder) replaces expensive steam-heated cooking vessels with mechanical energy to more efficiently cook and dry oilseeds ahead of the Expeller.
Regardless of the equipment used upstream, adding heat prepares the oilseed for more efficient pressing by rupturing the cells to release the oil, so it flows more freely through the Expeller.
What is cold pressing?
Cold pressing, by comparison, does not add heat to cook and dry the oilseed before extraction. Instead of using traditional steam vessels or extrusion systems to cook and dry the oilseeds, cold pressing skips these steps by sending raw material straight to the Expeller press.
Since this “cold” material hasn’t been cooked or dried to release the oil from the seeds, the screw press has to work even harder to extract the oil with pressure alone. This calls for more torque to squeeze the oilseeds harder and longer. Some processors achieve this by running multiple presses or multiple passes through the same press, which can be very inefficient. The Anderson Super Duo Expeller® utilizes two presses in a single pass to extract oil more efficiently, making it ideal for cold pressing.
But just because there’s no external heat added in cold pressing doesn’t necessarily mean there’s no heat involved. Heat often sneaks into the process early on, to dry the raw oilseed material for storage, and later on, through the form of friction in the press.
Drying Oilseeds for Storage: Keep in mind that whether you’re hot pressing or cold pressing oil, you still need to dry your raw oilseed material for safe storage beforehand. This is different from the drying step we just discussed, which uses heat to dry the cooked material to less than 5% moisture content immediately before extraction in a traditional hot press.
Drying oilseed for storage is a critical first step because if your material isn’t stored at the proper moisture level (below 12%), you risk losing it all to mold, mildew, and bacterial growth before you can even begin processing. Whether you proceed to hot pressing or cold pressing, you’ll always start by drying your material for storage. However, in the case of cold pressing, you won’t add heat to further dry the oilseed again before extraction.
Combating Friction in the Press: As with the original Expeller, the mechanical motion of the screw press naturally creates some frictional heat, even in cold pressing. In fact, with more torque comes even more friction. Cold presses must compensate for this heat by using a water-cooled shaft to keep the press cool during the process. Then, as oil is expelled from the press, it’s pumped through a heat exchanger to instantly drop the temperature of the oil and keep it cool.
Cold-pressed or “virgin” oils often demand a premium price in the market compared to traditional hot pressed oils, which can make cold pressing an attractive option to improve profits.
An expeller press can become a hot press or a cold press, depending on the steps you take upstream before extraction. Equating an expeller with hot pressing isn’t quite accurate because the screw press has nothing to do with the processing temperature. Whether you’re adding heat to cook and dry oilseed for hot pressing, or minimizing heat through cold pressing, you can achieve optimal efficiency for your facility when you have the right equipment for the job.
Now, instead of asking about the differences between expeller pressed versus cold pressed oil, you understand how to compare hot pressing and cold pressing — using an expeller either way to extract the oil trapped inside.
To learn more about oilseed extraction methods and machinery, contact the experts at Anderson International.