Cooking Oil Processing

There are major 3 steps for cooking oil processing:---

1.??? NEUTRA:ISATION/REFINING

2.??? BLEACHING

3.??? DEODOURISATION

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Major loss is the NEUTRALISATION LOSS in the whole process of Vegetable Ghee & Cooking Oil. So we have to give full attention on NEUTRALISATION.

? To control that loss we must know the theoretical neutralization Loss. Most of the technical Managers think that it is equal to FFA% x 2.5. But the experiences show that NEUTRALISATION LOSS depends upon the WESSON’S LOSS.

? So we have to first determine the WESSON’S LOSS of that edible oil which is going to be neutralized.

This Loss includes FFA, moisture, mucilaginous matters.

? After neutralization, neutral oil & TFM (Total Fatty Matters) of the Soap Stock, which is removed, must be determined, neutral oil should not be more than 1% if its TFM is 40%.

?I have discussed in details WESSON’S LOSS & NEUTRALISATION PROCESS in my earlier pages.

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Bleaching:--

? No doubt major losses are Neutralization Losses, but there is a need to control the bleaching losses also. Here I am discussing about bleaching losses.

For that first we have to understand the Bleaching process

The bleaching of edible oils and fats is a part of the refining process of crude oils and fats, which removes contaminants that adversely impact the appearance and performance of triglyceride (triacylglycerol)-based materials. Many of these impurities have to be removed from the oil to achieve the high quality oil standards necessary for edible applications. Preceded generally by degumming and refining (neutralization) processes, bleaching is required to remove specific detrimental contaminants that are not effectively removed by these processes before the oil progresses through deodorization.

The bleaching operation effectively removes some of the color, reduces the contents of chlorophyll, residual soap and gums, trace metals, oxidation products, and indirectly impacts on deodorized oil color. While the bleaching process appears to be a simple mixing of bleaching earth and oil followed by filtration, the chemical and physical reactions occurring are complex and greatly reliant on process variables (i.e. moisture levels, temperature, contact time, and vacuum), oil quality entering the bleacher. The success or efficiency of the bleaching operation is interdependent on the effectiveness of upstream processes where contaminants that have the potential to interfere with the bleaching mechanisms should be removed. Some consider bleaching the “safety net” of the refining process in that it is the last operation in the oil refining process before going to deodorization.

For better results we have to select the Fuller’s Earth that has the following properties:---

? Having the lowest oil retention.

? pH should be not less than 4.

? Bleachibility should be not less than 70%

? Moisture should not be more than 12%

Bleaching is the physical and chemical interaction of an oil or fat with bleaching earth to improve its quality. One definition of quality is “to reach a level of excellence.” However, with respect to oil specifications, it is quite variable and depends on the product and market we are dealing with. For example, for deep-frying oils, it is very important that phosphorus (P) be as low as possible and a residual content of <0.5 ppm is desired.

Various processing conditions can affect one or more of the oil characteristics that have been listed in quality specifications. By balancing these conditions one against the other, you will be one step closer to a more efficient bleaching process.

If we acquire the following results, then that will be called efficient process.

? Soaps are completely removed

? Phosphorus content is reduced to below 2 ppm

? Iron content is reduced to below 0.2 ppm

? Chlorophyll content is reduced to below 0.05 ppm

? Peroxide Value is reduced to below 0.5 meq/kg

There are numerous interactions between the process variables that influence the removal of oil contaminants and the efficiency of the bleaching process.

Fuller’s Earth dosing in bleaching operations is typically controlled by monitoring bleached oil red color and/or chlorophyll; they are two of the easiest parameters to measure.

Temperature

Oil bleaching temperatures typically range from 90–125°C (195–257°F). Temperature affects oil viscosity and adsorption kinetics. Oil viscosity decreases with increasing temperature resulting in better dispersion of bleaching earth particles, improved clay/oil interactions, and less resistance to flow. The ability to maintain a particle in slurry suspension is inversely related to the viscosity of the oil, implying that bleaching earth with coarser particle size distributions (PSD) will require a more powerful agitation to stay in suspension and that with finer PSDs may more rapidly disperse into the oil at higher temperatures. A higher temperature may give you benefits on chlorophyll removal, color, and filtration rates, however, depending on oil type and oil quality, may in turn worsen the color of the deodorized oil, and its oxidative stability.

Contact time

The contact time between the oil and the bleaching earth refers to the total time that the bleaching clay is in contact with the oil. Times typically range from 15 to 45 minutes, with 20 to 30 minutes being most common. In batch systems, contact time tends to be longer due to the sequential nature of the batch process. The positive effect of increased contact time is that it may improve bleached color and chlorophyll removal.

Oil moisture content

To reiterate, the optimal level of starting moisture in oil to improve bleaching is not fixed. We have to dry the oil first. Bleaching Earth which we used is already containing the moisture contents upto 10%.

Vacuum

Bleaching efficiency improves when operating pressure in the bleacher is run between 50 to 125 mmHg (absolute). Reduced pressure allows for a smooth water evaporation rate resulting in increased efficiency for removal of phospholipids, chlorophylloids, and some red pigments. Reduced pressure also minimizes interaction of oil and air resulting in lower peroxide values, anisidine values, and bleached oil color.

Bleaching efficiency is highly dependent on the interaction between vacuum, moisture and temperature.

The absolute pressure of the vacuum works in conjunction with temperature to drive moisture out of the oil. Depending on the incoming moisture levels, too strong a vacuum can be detrimental for bleaching efficiciency in that it will pull moisture out of the system too quickly and drive moisture to below the optimal range (0.06 to 0.1%) to reap its benefits (reportedly as much as 30% improved activity). The process is deemed optimal when the moisture content of the oil leaving the filter press approaches 0.05 weight % from the high side of the optimal range.

Filtration

The filterability of adsorptive minerals, including clay minerals and diatomaceous earths (DE), depends on the natural (or created) porosity, the particle size distribution (PSD) of the product, and the type of filtering aids (DE, cellulose fibers, paper, etc.) and equipment employed. In general, the flow of oil through a given adsorbent bed can be improved by increasing the particle size and/or decreasing the range of the PSD. Permeability of the filter bed also depends upon the interaction between the particles in the system with respect to the PSD of the bleaching adsorbent, the amount of filter aid employed as pre-coat, and the mesh size of the filter media (paper, screens, cloth).

To arrive at an optimal bleaching process, you must first establish what the primary target specifications will be and make sure that you are getting the appropriate contaminants removed by the overall refining process

? Low in phosphorus (good if <15 ppm, very good if <10 ppm and excellent if <5 ppm)

? Low in free (unesterified) fatty acids (FFA <0.1 % unless some adaptation of physical refining is being employed)

? Low in soaps (<50 ppm unless silica/silicate refining is used)

Once you have this under control you can begin the bleaching stage where:

? Soaps are completely removed

? Phosphorus content is reduced to below 2 ppm

? Iron content is reduced to below 0.2 ppm

? Chlorophyll content is reduced to below 0.05 ppm

? Peroxide Value is reduced to below 0.5m.eq/kg

All values cited herein serve as industry guidelines to meet product specifications. Each refinery is unique, having any assortment of equipment and production lines set up to meet customer driven specifications.

To control the Bleaching Losses:--

*Minimum quantity of Bleaching Earth should be used to achieve the above mentioned results.

*The Oil Contents in Spent Earth (used Fuller’s Earth) should not be more than 25%.

??? Keeping in mind, one bag(25Kg) of Fuller’s Earth retained 8.25Kg minimum oil, so try your best to use minimum Fuller’Earth(as per requirement) to minimize the bleaching losses.

FARHAT AZM

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