According to Ruistars, sesame is mainly distributed in Henan, Anhui, and Hubei, followed by Liaoning, Hebei, Shandong, Jiangsu, and Jiangxi in China.

The oil content of sesame is between 40% and 58%, and the fatty acid composition of triglycerides is relatively simple as shown in Table 1. The content of vitamin E in sesame oil is not high (50mg/100g oil), but it is very stable and has a long shelf life. This is due to the presence of about 1% of natural antioxidants such as sesamol, sesamolin and sesamin in crude sesame oil.

In China, sesame can be extracted by water, pressing, or pre-pressing and leaching. However, the production scale of the water-based method is generally small, the processing is scattered, the process is old, the equipment is backward, the labor productivity is low, the residual oil of sesame residue is high (generally dry base 9% to 12%) and the water content is high (moisture can be as high as 65%), sesame residue is easily spoiled and smelly, the utilization rate is poor, generally used as fertilizer or dried for feed. In addition, due to the high frying temperature of the seeds, some components coke at high temperatures and become bitter, which affects the quality of hemp residue.

The advantage of water-based oil production is that the oil produced has an excellent aroma and is no less efficient than that produced by pressing. At the same time, the equipment for water-based oil production is relatively simple. The disadvantages are the low productivity and the high water content of the oil cake residue, which is not easy to preserve.

Sesame oil produced by machine presses, called “big trough oil,” has a strong aroma, but is less fragrant than “small mill oil.” Due to the high oil content of sesame, two presses are needed to increase the oil yield, resulting in higher power consumption, darker oil, and less aroma. It is also produced with more oil residue and filter cake. However, the press cake can be leached to make oil. After leaching, sesame oil has lost its inherent flavor due to a series of refining, and is used only as a general cooking oil.

Water-based oil production

(1) The basic principle of water method of oil extraction

water method of oil extraction is different from the pressing method or leaching method in principle, therefore, using the non-oil components of oil on the different affinities of oil and water, add the right amount of water to the prepared oil, after a series of procedures, the oil and hydrophilic proteins, carbohydrates and other separation.

Frying the seeds is extremely special

The role of sautéed seeds is to make the protein denaturation of the oil cell structure in the colloid coalescence of cellular tissue destruction, so that scattered tiny droplets of oil aggregation, sesame seeds after sautéing, from the original astringent and unflavored become fragrant and crispy, so that the system made of sesame oil has a special flavor.

Transformation of dispersion system

Due to the high oil content, the paste is transformed from a gel into a coarse dispersed system of solid particles in liquid oil, where the solid particles are discontinuous dispersed phases and the oil is a continuous dispersing medium. This system is more stable and the oil and solids in the sauce are difficult to separate on their own in storage. The finer the grinded seeds, the better it is, so that water can easily penetrate into the sauce when the oil is being added to the pulp, absorbing water evenly and replacing oil completely.

Water instead of oil

Mixing and stirring the oil is the key to aqueous extraction of oil. The solid particles in the sauce are mainly proteins, carbohydrates, and combinations of proteins and other substances. These polymers contain hydrophilic and lipophilic groups. These polymers contain both hydrophilic and lipophilic groups, and can be wetted by both water and other substances. However, since the hydrophilicity of these compounds is far more dominant than the lipophilicity, their ability to bind to water molecules is much stronger than that to oil.

When boiling water is added to marijuana and stirred, the water comes into contact with the solid particles and is absorbed by the solids. Solid particles absorb water, on the one hand, due to the expansion of water absorption, the volume increases, and thus the molecular energy decreases, so that the solid surface can be reduced, on the other hand, due to the solid surface molecules on the water to produce a strong attraction, making the original oil occupied part of the solid surface was replaced by water, with the increase in water absorption of solid particles, oil on the solid surface of the combination of energy gradually decreases, the oil and the solid surface of the gradual separation. However, in reality, the solid surface cannot be completely replaced by water molecules, and therefore, the oil is not completely removed.

The amount of water added to the sauce is based on the maximum amount of water absorbed by the solid particles, thus maximizing the effect of water instead of oil. However, if too much water is added, when free water is present, it can cause emulsification, mixing the oil, water and paste residue together and making it difficult to separate them. At the same time, the pesto is thin, the viscosity is reduced, the surface tension is weakened, and the oil layer is easily mixed into the pesto when skimming. If too little water is added, the resulting residue is too viscous and the oil droplets do not float easily when the oil is shaken and separated.

When the sauce is mixed with water for a certain period of time, it becomes so thick that even the oil disappears. This is due to the fact that the solid particles of the sauce gradually absorb water and swell, causing the distance between the particles to diminish and the oil droplets that were previously visible to be stirred into the sauce. When the particles have absorbed enough water to form a hydrophilic surface, the oil is gradually discharged, and the entire sauce is thinner and thicker. The oil is gradually discharged and the sauce becomes thinner and thicker. The oil between the particles becomes more and more, and the distance between the solids becomes larger and larger. The role of the oscillation of the separation of oil: The oscillation of the gourd is to cause the internal squeezing and oscillation of the pesto, to help the oil droplets wrapped in the pesto interior to collect and float. The proper temperature should be maintained during shaking to reduce the viscosity of the oil and facilitate separation.

(2) Water substitution process

Process:

Sesame seeds→Sorting→Rinsing→Frying→Frying the seeds→Smoking→Blowing→Milling the seeds→Adding the pulp→Churning the oil→Shaking and separating the oil→Small grinding of aromatic oil
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Sesame

Cleaning:

The purpose of cleaning is to remove impurities and immature seeds.

Rinsing:

It can remove the residual microscopic impurities after sifting to make the sesame seeds cleaner; in addition, soaking the sesame seeds in the pool for an hour to make them evenly penetrate the water, so that the protein denaturation can be more complete and perfect when frying the seeds, and also extend the frying time to avoid the phenomenon of scorching, frying paste or scorching inside and outside. Usually oil factories use washing machine for rinsing, and the water content of sesame seeds after washing is about 35%.

Frying:

When frying sesame seeds, it is important to master the fire, time and temperature. In the beginning, due to the large water content of sesame, it is advisable to fry the material rapidly; when the frying degree reaches 70%, reduce the heat, and always check the tenderness of sesame, generally so that the temperature reaches about 200 ℃ is appropriate. The cooked sesame seeds are red or yellow-brown when twisted by hand. When frying the ingredients, turn them frequently so that moisture and smoke can be easily dispersed to prevent scorching and uneven ripening of the sesame seeds. At the same time, according to the different varieties of sesame seeds, in the specific operation of the treatment, the thick skin should be high heat, the thin skin should be low heat.

Special attention should be paid to the sesame seeds, pouring a proper amount of cold water into the frying pan to cool the sesame seeds when the frying time is right (about 30 minutes and 190℃～200℃). The sudden drop in temperature makes it easier to crisp up the structure of the sesame seeds, making it easier to grind the seeds finely. It also helps to lower the temperature of the sesame seeds before serving to avoid scorching. The sesame seeds can be sautéed by human or mechanical stirring, and the speed of the powered stirrer is usually 40-45r/min.

Smoke:

When the sesame seeds are put out of the pot, although water is poured to cool down the temperature, the temperature is still around 140℃～150℃, if not cooled down, there is still a possibility of scorching, so the heat should be dissipated immediately after the pot is put out of the pot. Therefore, it should be cooled off immediately after cooking. Therefore, it is called “lifting the smoke”. Smoke lifting operation can be carried out by smoke lifting machine, but in small oil factories, it is usually carried out manually.

Blowing:

During the frying process, the sesame skin easily falls off, and some of the frying paste (commonly known as sesame bran) is mixed with the sesame, which contains less oil and affects the quality of the oil, so it must be removed. The blowing operation is usually done by blowing or sifting.

Seed grinding:

Sesame seeds are ground to a paste in a stone or emery wheel grinder after being fried and blown clean. When sesame seeds are ground, the presence of oil results in a paste, usually called masa (as opposed to the normal edible sesame paste that is ground when fried young).

When grinding the seeds, add ingredients evenly to prevent empty grinding. The seeds should be grinded as they are cooked, but not too much. The temperature of sesame seeds should be kept high, generally 65℃～70℃. If the temperature is too low, the sesame seeds will not be finely ground. If the grinding speed is too high or the temperature is too high, the flavor of the oil will be affected.

Adding water is an important part of refilling the oil. According to the test results, the optimum amount of water to add is twice the amount of non-oily substance in sesame seeds (about 83% of the weight of sesame seed pulp). For the first time, add 60% of water, keep the water temperature above 90℃, and stir continuously for 40-50 minutes. For mechanical stirring, the speed is about 30r/min. After adding water, the masa is easily thickened, so it must be turned evenly, otherwise, it is easy to lump together uneven draught. Stirring to maintain the temperature in the pot at 70 ℃ or more, 40 minutes after the consistency is reduced, there are very small particles appear, the particles covered with a very small amount of oil.

The second addition of water is about 20% of the total amount of water added (water temperature of 90 ℃ or more). Stirring was continued for 40 to 50 minutes with manual turning (temperature maintained at 60°C). At this time, the granules gradually became larger, there was more oil outside the granules, and some of the oil began to float.

The third addition of water is about 15% of the total amount of water added (the temperature is maintained above 90℃). After 15 minutes of stirring with manual assistance, most of the oil floated to the surface and the sauce at the bottom formed a honeycomb shape, making flow difficult. The temperature was maintained at about 50°C. The last addition of water (sizing) was done with the help of a stirrer.

The last addition of water (sizing) should be at discretion. When the temperature is adjusted to the appropriate level, reduce the stirring speed to 10r/min without manual turning, and after 1 hour, most of the oil will float on the surface. After skimming, the surface should retain about 7 to 9mm of oil layer to prevent the material temperature from dropping too quickly.

Vibrating oil:

After the above treatment, there is still some oil scattered inside the slurry, which can then be separated by vibrating method (pier oil). The dun oil is still made in the redemption pot, and the rotational speed of the pot is 10r/min. when dun oil is made, two copper gourds are used to move up and down, so that when the gourd is rammed down, the center one is about two-thirds of the gourd and the side one is only one-third of the gourd. After about 50 minutes of deep pier, the surface oil increases, and then the shallow pier for an hour, so that the second skimming can be done. Then, after 50 minutes of deep pier, the third skimming can be done. After the deep pier, the gourd is raised appropriately, and then the shallow pier for 1 hour, the fourth skimming. The amount of skimming depends on the temperature; more skimming and less staying should be done in summer and less skimming and more staying should be done in winter in order to keep warm.

Oil extraction by sesame press method

Process Flow:

Sesame seeds→Screening→Rinsing→Frying the seeds→Smoking→Blowing→Pressing→Oil wool→Precipitation filtration→Sesame oil
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Sesame Cake → Second Pressing

The pressing of sesame seeds for oil is characterized by the preservation of sesame oil flavor, for which the conditions of heat treatment are critical. This is because the proper increase of pressing temperature facilitates the conversion of sesame ethers into sesamol, which has a special flavor. The oil can be extracted by pressing with two presses under the condition of “frying the seeds” of the water method, but the temperature should not be too high, otherwise the oil will be blackened and the cake will be bitter. The advantages of the cake meal is low water content, can be stored for a long time.