A practical guide for nutritional and traditional health care.
Although it may seem incredible, most people generally have wrong notions regarding oils that are labeled ‘cold-pressed'. In fact, majority of the people, which includes the owners of stores selling cold-pressed oils as well as the customers, are of the erroneous view that oils that are said to be cold-pressed stay cold while they are being pressed. This is an entirely wrong interpretation of the term ‘cold-pressed'. There are people who believe that oils sold under the label ‘cold-pressed' are of superior quality vis-à-vis nutritional properties and they are right, to some extent, when they believe that oils that are cold-pressed are spoilt when they come in contact with heat. Since, most people have wrong notions about cold-pressed oils, before we move ahead on this topic, it is essential to know the precise meaning of the term ‘cold-pressed'.
Precisely speaking, oils that are labeled as ‘cold-pressed' are basically unrefined oils, such as olive oil, that are produced by pressing the parent seed, grain or nut at the minimum possible temperature. In other words, the process involved in producing cold-pressed oil uses a low heat procedure. It may be noted that introducing heat to the process involved in producing cold-pressed oils will reduce or vitiate the oil's essence, color as well as its dietary importance. Nevertheless, it has been found that introducing heat to the process augments the yield of the oil. This is the primary reason why cold pressed oils are generally very costly and, at the same time, cold pressed oils are of superior quality compared to oils produced through other processes, such as applying heat.
It may be mentioned here that the phrase ‘cold pressed oil' is actually dependent on diverse parameters, especially subject to the region of the globe where it is being produced. For instance, the oil that is sold under the label ‘cold-pressed' in the European Union ought to be made in an environment where the temperature never goes beyond certain degrees. Although the temperature may differ vis-à-vis the parent seeds or nuts that are being processed to produce the specific ‘cold-pressed' oil, under no circumstance should it exceed 80° Fahrenheit or 27° Celsius. On the other hand, the oil marketed as ‘cold-pressed' oil in the United States is actually not standardized and, hence, ‘cold-pressed' oils sold in that country may not be the genuine ‘cold-pressed' oil whatsoever. In order to ascertain the genuineness of any oil sold under the label of ‘cold-pressed' oil, it is essential for the consumers to smell and taste the oil before they buy them. Only by smelling and tasting the oil, they are able to verify whether the oil labeled as ‘cold-pressed' is actually so.
Generally, the procedure adopted to make cold pressed oils from seeds, nuts or fruits involve grounding these substances to prepare a smooth paste. Subsequently, the paste is made to undergo a malaxation (a kneading technique) process. In other words, the paste is stirred slowly and this action persuades the oil enclosed by the paste to clump. Next, the oil is extracted by applying pressure to compel the oil to come out of the paste. In case heat is applied to the paste, it will increase the yield of the oil. There are some producers of cold pressed oil who add warm water to the paste or heat the paste before pressing it to extract the oil. Alternately, some other producers use an altogether different technique to make cold pressed oils. They simply use an oil stone (a chunk of fine-grained stone that is generally oiled) to separate the oil from the paste. Once the oil has been produced, it is categorized according to its superiority and then bottled for shipment.
There are a number of manufacturers of cold pressed oil who produce a variety of the oil known as ‘expeller pressed oil'. This particular type of cold pressed oil is produced in an environment of high pressure. Such high pressure is occasionally essential in the instance of using thick seeds and nuts to produce cold pressed oils. However, this process generates heat owing to friction in high pressure conditions. Some of the expeller pressed oils may also be described as cold processed oil as the temperature does not go up much during the process involved in producing these oils. On the other hand, expeller cold pressed oils that involve significantly high temperatures cannot be termed as cold pressed oil simply because of the extreme heat used to produce them. In such cases, the manufacturers may distinguish between the two oils by labelling them aptly. Those that are produced in high temperature conditions may be labelled as ‘expeller cold pressed oil'.
Several cooks are of the view that cold pressed oils possess a better-quality essence and, hence, they are very active in seeking this type of oil. It may be noted that cold pressed oils are usually better compared to other types of oils when it comes to dressings as well as preparing dishes wherein the essence of the oil plays a significant role. Nevertheless, when the cold pressed oil is heated while cooking, consumers or cooks ought to be more worried regarding the smoking point of the oil that they may be using to prepare the dishes. There are a number of cold pressed oils that cannot endure high temperatures and, therefore, these types of oils should never be used for culinary purposes. If they are used for cooking, their subtle and intricate essence is bound to fade away.
The saga of cold-pressed oils
It is interesting to note that the term cold-pressed is yet to find a precise meaning. Although it may seem to be strange, the fact remains that neither the government nor the industry engaged in producing ‘cold-pressed' oils have arrived at a consensus regarding a definition for the term. In such a situation, all are at liberty to invent their individual definitions for the term ‘cold-pressed' according to what suits their personal objectives.
In fact, there is one producer which terms all oils that have been heated to extremely high temperatures during the deodorization or amortizing as ‘cold-pressed' since they have not applied any external heat to the seeds during the pressing process. However, the definition of ‘cold-pressed' offered by this company contradicts the fact that it is never essential to apply external heat in the sophisticated presses, as the process of pressing itself generates heat owing to pressure as well as friction caused by the rotational movements. In addition, this definition of ‘cold-press' also disproves the heat applied to the seeds and nuts prior to as well as after pressing them. This includes the deodorization process during which temperatures above 200°C or 400°F are maintained for anything up to an hour.
The term ‘cold-pressed' has actually been derived from German words. In fact, this term is a translation of the German words ‘kalt geschlagen', which literally denoted ‘cold pummeled'. Around a century back, oil was produced domestically in an extremely sluggish, mallet-hammered and manually operated wedge presses in Germany. First, the seeds were transferred into a container that had the shape of a wedge and a wedge made from wood was driven to it. The housewife would thump the wedge with a wooden mallet at intervals of an hour and this would make the oil trickle from the wedge for about an hour. After another interval, the housewife would hit the wedge again to ensure that oil continues to drip for another hour. The lady would continue this process throughout the day to obtain the oil required for her household. In effect, the words ‘kalt geschlagen' actually denoted that the oil was produced without applying any heat either to the seed or the oil. By this process, the Germans produced entirely natural, fresh, unrefined crude and superior quality oil.
Till this day, the term ‘kalt geschlagen' is used by people in Germany even for oils that are produced using most modern and sophisticated methods. Although the modern methods engaged in producing oils are entirely different from what it had been a hundred year ago, people like to use the term as for oils that are of superior quality. Even in North America, people use this term extensively for oils that are produced by methods that involve applying heat to the seeds and nuts or the oil itself.
The truth is that in the present times, it is nearly impossible to find any oil that has not been produced commercially by applying heat. However, it needs to be noted that ‘virgin' olive oils are a rare exception in this regard. Another exception is a peanut oil brand that is available in natural foods trade. This oil is still produced by the old hydraulic pressing technique that does not produce any heat. Baring these two oils, most other commercially available oils are made by applying external heat.
It may be noted that around 80 years ago, when hydraulic pressing technique was the only method to produce oils commercially, manufacturers cooked the seeds before the pressing process with a view to enhance their oil yield. In fact, the screw presses (mechanical or the expeller process) also create heat owing to friction while the seeds as well as the crushed substances are compressed concurrently and spun around into a squeeze. Application of external heat actually makes the oils come out of the seeds more quickly. In effect, the more the heat, the less amount of oil is left behind in the pressed seed cake. At the same time, it also means more efficiency in operation, higher prices and more profits along with very little wastage of the oil.
In order to obtain oils using the expeller pressing method in small presses, one needs to apply a minimum external heat of approximately 50°C or 122°F. While no oil can be produced by this method using lesser heat, the heat inside the press head is actually much more than what is being applied externally. Within the small presses, the temperature often goes up to anything between 54°C and 72°C, which is equivalent to 130°F - 160°F. In presses that are a size up, the heat goes up to approximately 65°C to 85°C or 150°F to 180°F. However, when you are using large presses to produce oil, the temperatures go up much higher. In the oil producing industry, it is a regular trend to gauge the lower temperature at which the oil trickles out of the press. This lowest temperature of oil dripping from the press is known as the ‘pressing temperature'. However, many feel that it would be more appropriate if it is termed as the ‘dripping temperature'.
When the term ‘cold-pressed' is used in Switzerland, it denotes that the temperature has never gone beyond 50°C or 122°F during the entire process of making the oil from the seeds to the oil being bottled for sale. However, there is no fixed definition for the term ‘cold-pressed' and, hence, everyone is free to invent as well as use his/ her definition. The normal temperature at which oil begins to drip or trickle out of huge presses is around 95°C or anything between 185°F and 203°F. Within the press, the heat is always a little higher and there are a few presses that produce so high temperatures owing to the very high pressure and friction at which they function that the oil that trickles out of the machines actually has a somewhat burned flavour. Since there are people who have a preference for such burned taste of oils, several producers market a number of brands that possess addition burned tastes or flavour to cater to the preference of this category of consumers.
Pressing oil using least temperature
There are basically two primary reasons why oil needs to be pressed at the lowest possible temperature. In other words, it is always better to produce oils applying the least amount of external heat.
Firstly, while the temperature inside the pressing machines goes up due to application of more external heat, the chemical reactions also accelerate. Precisely speaking, the speed of the chemical reactions with the seeds, crushed materials and oils inside the pressing machines increase over two-fold for a rise of every 10°C (18°F) in the heat applied externally. The more the temperature of the oil being produced by the pressing machines, the oil is destroyed or spoilt more rapidly by oxygen, light and other chemical effects. The rate of destruction of the oil may be diminished by completely shunning air and light from the pressing process. However, it is unfortunate that usually most pressing facilities operate without taking these protective measures.
Secondly, when the temperatures are high, it results in internal changes in the oil molecules, which damages the oil faster. In such cases, any unsaturated fatty acid is likely to change into aberrant trans-configurations. Alternately, the fatty acids may also oxidize, crosslink, dimerize (react to form a dimer - two identical molecules) or polymerize transforming the form as well as characteristics of the molecules of fatty acid. In turn, these destroy the nutritional as well as biological significance of the fatty acids and even make them toxic.
Generally, such chemical reactions and internal changes in the oil molecules start occurring noticeably as the temperature of the oil touches 160°C or 320°F and they turn to be very grave when the temperature exceeds 200°C (392°F). In fact, the temperatures seldom go beyond 100°C or 212°F during the oil pressing process. Therefore, the heat generated during the pressing process itself is not the main setback provided air and light is prevent from coming in contact with the oil being produced. Keeping this aspect in view, it may be said that the ‘cold-pressing' process is completely rooted in fiction and unawareness. In reality, ‘cold-pressing' does not provide any value advantage to the oil produced by this process.
In effect, the term ‘cold-pressing' is insignificant or without any worth. Rather, it may be said that the manufacturers use this term unethically simply with the view to cater to the consumers who are not only ignorant, but also think that oils produced by the ‘cold-press' method are simply of superior quality. As far as the quality or excellence of the oil is concerned, it is more imperative that the oil is secluded from oxygen and light during the pressing process. In addition, the oil also needs to be protected from these agents when it is being bottled, stored and shipped.
The process of deodorization or getting the oil rid of the unpleasant odour continues for approximately an hour at very high temperature (approximately 245°C or 473°F) actually spoils the nutritional value of the oils and also generates trans-fatty acids as well as results in chemical transformations.
At the same time, the hydrogenation process, which is undertaken to change liquid oils into semi-solids or hard fats, continues for several hours at temperatures as high as 250°C (482°F). The hydrogenation process is carried out to deliberately produce trans-fatty acids since they melt at a relatively high temperature and are also more solid compared to cis-fatty acids. In addition, the trans-fatty acids help to provide body, stability, texture and shelf life to products made from oils - substances like margarines and shortenings.
Trans-fatty acids are also produced when something is fried or deep fried using oils, particularly when the oil is allowed to heat and boil for many hour, or sometimes even for several days, at temperatures ranging between 160°C and 220°C (320°F to 428°F) conditional on the type of oil being used. In addition, allowing the oil to boil for a prolonged period also produces chemical destruction of fatty acids induced by heat, oxygen and light.
Although it is advisable to keep the pressing temperature or the heat produced during the pressing process at the lowest possible, actually the pressing temperature is not the main problem during the process of oil manufacture provided the producers are able to bar air and light coming in contact with the oil. However, what is of great concern is the temperatures at which different other processes, including deodorizing, frying and hydrogenating, are carried out.
Before wrapping up the discussion, it may be rightly stated that the term ‘cold-pressed' is actually founded on a misconstruction. In reality, ‘cold-pressed' is of no value at all. It does not help to determine the quality of oils in any way whatsoever.
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