AMF Production Line

Overview

The central objective of the AMF process is to break down the oil-in-water emulsion and separate all non-milk-fat components. Two variants are possible: either the direct route via raw milk skimming after which further processing / concentration of the cream takes place , or from butter. As a result of the flexible process and automation process structure, cream as well as sweet cream and sour cream butter can be used as basic materials for making AMF.

Process of making AMF from cream

The flowsheet shows an example of making AMF from cream.

An NaOH treatment can also be integrated, thus enabling the content of free fatty acids to be reduced. Various process parameters and variables can be entered in the installation control facility for the various materials and qualities; these process parameters and variables automatically adjust all regulations and function procedures to meet the needs of the specific product.

Standard process

Cream with a fat content of approximately 40 percent is fed into this installation, and is initially heated to a temperature of 55 to 60 °C in a plate heat exchanger. This temperature is necessary to ensure that the cream to be concentrated in the separator bowl has a minimum viscosity and that there is a maximum density difference at the same time between the concentrated cream phase and the serum phase. A cream concentrator then concentrates the cream to up to 75 percent fat. This concentrate is now sent to the phase inversion process. The separated serum is pumped from the separator to the butter milk tank after cooling and heat recovery. This means the still warm serum is used for heat recovery, which also has a positive influence on the energy efficiency of the entire system.

As is the case in the process of making butter, the initial objective is to break down and separate the fat globule membrane in order to achieve phase inversion. The membranes of the fat globules can be broken down by means of mechanical energy. The fat release process and the associated phase conversion process take place by splitting the intact fat globules by mechanical means in a homogenizer. The following aspects are extremely important for effective phase conversion: concentrating the cream in the feed to the homogenizer, the design of the homogenizer, the homogenization pressure and special recirculation of the phase-inverted medium.

In the downstream oil concentrator, the emulsion and serum, as the heavy phase, are separated from the light oil phase and recycled back into the cream concentration stage. On the other hand, the light oil phase with a concentration up to 99 percent is heated to a temperature of approximately 90 °C and washed after the addition of water. In the oil polisher the wash water is separated and the remaining water content is reduced in a vacuum evaporator. In this process stage,the recovered butter oil has an oil content of at least 99.8 percent, and thus meets the requirements for the highest quality category. Before the AMF is transferred to storage it is cooled down to approximately 50 °C.

Cream concentration

Cream concentrator

Cream concentration is carried out with specially adapted milk separators that are rated for the concentration of a viscous cream. The preheated cream is conveyed from the plate heat exchanger directly into the separator feed. Concentration takes place in the separator from 35 – 42 percent to 72 – 75 percent fat. This fat content must be reached as minimum so that the downstream process stages are optimal. The highly viscous cream is forwarded directly via the shortest route possible into the so-called high-fat tank which serves as a buffer upstream of the homogenizer and phase inversion. The separated serum is conveyed into a storage tank after heat recovery and final cooling.

Phase inversion

Phase inversion

In its normal state, milk fat forms a stable emulsion with water of the oil-in-water variety. To stabilize the emulsion, the fat is enveloped in an adsorptive covering of phospholipids and proteins. 

The break-down of this emulsion and separation of all non-milk-fat components is the aim of AMF production. It is possible to break down the membrane by means of mechanical energy or a chemical reaction. Mechanical energy (e.g. homogenization) is used to break open the membranes. Smaller fat globules are formed by the newly created membranes, which themselves were created by the fragmentation of the original membranes and from the proteins in the milk serum.

Reduction of the fat globules is also employed, for example, in the processing of drinking milk, in order to prevent the so-called “creaming” effect.

Complete phase inversion is  not possible with this process. Furthermore, a relatively stable emulsion layer is formed from the existing amount of cream and part of the serum; this impedes separation as a third layer between the oil and serum phases.

Special measures are necessary if the reversible process of formation of new, intact fat globules is to be minimized.

The following applies for minimizing the emulsion content: the three fractions, namely fat, phospholipids and proteins, are largely responsible for a stable emulsion. If one of the three fractions is removed, or is changed to such an extent that it can no longer be used as a building block for the membranes, then the formation of intact fat globules is prevented and the formation of emulsion is not possible.

When all the above-mentioned parameters are applied to phase inversion, they result in a degree of inversion of 80 – 95 percent.

Unlike standard homogenization, the aim is not to reduce the size of the fat globules but to destroy the membranes or envelopes so that the fat can be recovered. It is therefore important to prevent the formation of fat globules with intact new membranes.

An initial conclusion from the above is that the amount of serum should be minimized before the start of actual production of the oil, so as to minimize the amount of available membrane building blocks.

In order therefore to achieve adequate release of fat, a cream fat content of greater than 75 percent is required which is realized in the cream concentrator. The release of the fat, and the phase inversion brought about by this, take place by mechanical fragmentation of the intact fat globules in a homogenizer.

Phase inversion - Homogenizer

Oil concentration

Oil concentrator

Following phase inversion, further concentration of the fat is by means of the next separation step, the oil concentration takes place. In contrast to the first concentration step, this step is no longer carried out with the classic milk separator but with a special oil separator. In contrast to a skimming separator, the configuration of the disk stack is fundamentally different. This is firstly due to the changed volume streams, the fat phase now accounts for the greatest portion, and secondly the focus is now on the purity of the oil.

This becomes clear when one looks at the cross-section of the bowl of an oil separator. The rising channels are towards the outer edge in order to achieve the longest possible path for the oil and, accordingly, a high level of purity. The oil must be as free from proteins as possible to avoid renewed emulsification in further processing. The fat content of the serum plays only a secondary role in this process step.

In this step, the product is concentrated from approx. 72 – 75 percent fat to approx. 99 percent fat. The emulsion phase referenced above and the serum are separated as heavy phase. The emulsion in particular is separated by a special bowl design. 

Depending on the proportion of free fat produced by the phase inversion, the fat content of the serum is between 15 – 25 percent. Due to the previous step of phase inversion, the serum of this separator contains a very high content of phospholipids and lecithin which is comparable with that of a butter milk from the classic butter churning process. 

The serum is fed into the balance tank upstream of the cream concentrator. By this means, the fat is separated from the serum again during cream concentration. The serum skimmed in this way is discharged from the process as a mixed phase, which means only one serum stream is produced here. Before the next separation step, the concentrated oil is heated to the corresponding process temperature of approx. 90 °C.

Oil polishing

Oil composition without and with polishing

The concentrate and heated oil is “polished” in a final separation stage. This step guarantees the high level of purity of the AMF demanded in accordance with the codex. The drawing above shows the oil composition without polishing in the upper section and the composition with polishing in the lower section.

To achieve further “purification” of the oil, a defined quantity of hot water is added to the concentrated oil. This water dilutes the concentration of the oil and consequently also the content of the lactose and ash still present.

The water added is separated immediately again in the so-called polishing separator. The oil purified and concentrated in this way is concentrated to approx. 99 percent fat. The separated serum-water mixture contains the still separated milk constituents and a very low fat content in addition to the water added. To assure a water content smaller than 0.1 percent in the oil, the oil is conveyed to the last process step before it can be cooled and packaged.

Oil drying / vacuum dryer

The 90 °C hot oil is fed to a vacuum dryer after polishing. The product inlet is designed to ensure as large a surface as possible and consequently good evaporation of the water out of the oil. An installed condensator and vacuum pump reduce the pressure in the vessel to approx. -0.9 bar, so that the water is evaporated at a temperature of below 100 °C. The same pump sucks in the vapors produced. Before they are discharged from the closed system, flash cooling takes place. Possible residual fat components, which are removed with the vapors, are separated in a skimming tank and thus do not burden the waste water systems.

The oil is separated from the lower section of the evaporator unit and transferred / pumped to the cooling stage.

FFA reduction

FFA (= Free Fatty Acids) in the end product oil result as a rule in a loss of quality. Furthermore, IDF standards place a maximum limit on the FFA content (figure 1). If the FFA content is to be reduced, e.g. because the initial values are too high, this can be achieved by physical and chemical means.

Free fatty acids are short-chain fats, such as butyric acids, caproic acids and carminic acids. There are problems of taste (rancidity) and/or aroma if the above are present in sufficient concentrations.

Free fatty acids result from the process whereby lipase enzymes adhere to the fat globule membrane and break down free fat over a period. It is necessary to consider

that the activity of the enzyme is very slow at low temperatures. Its maximum activity is at about 37 °C. Above 50 °C, its activity is minimal, and its activity stops completely at higher temperatures (> 60 °C). Assuming that there may be a relatively high FFA content in the initial product, namely cream and butter, it may be necessary to take special measures in order to remove the free fatty acids from the product.

A saponification process can be used to reduce the FFA content. Addition of lye (product-pH-value > 11) causes the free fatty acids to “saponify”.

The resulting flocculate can then be separated out in the polishing separator. The phase produced must be removed completely from the process.

Peroxide numbers

The quality of the butter oil is also determined by the peroxide number which expresses the milliequivalents of oxygen Obound by peroxide in one kilogram of oil. Oxidation of fat that has already occurred cannot be reduced as a rule; however, it can be suppressed or kept constant for a certain length of time. This is achieved by the addition of so-called antioxidants.

Antioxidants are additives which prevent an increase in the peroxide number of the oil, and to some extent reduce the peroxide values already present. Tocopherol can for instance be used.

The final concentration of tocopherol in the butter oil must be less than 200 ppm. GEA has the know-how for preparing and adding substances of this nature.

Secondary Skimming

Secondary skimming in contrast to the standard process

Beta serum secondary skimming

During centrifugal separation of the product, most of the free phospholipids migrate into the serum. For this reason, it is necessary to calculate the content of phospholipids in order to determine the yield of the “heavy phase” from a butter oil process. Pasteurized cream is normally used. The main difference with respect to the standard process is to be seen in the fact that a serum phase is recycled, as the phospholipids are released from the fat globule membranes during the phase inversion process.

In contrast to the standard process, separate skimming of the serum separator from the oil concentrator takes place here. The serum from the oil separator is collected in a buffer tank and fed from there to the so-called beta serum skimmer. The fat separated here is sent directly into the actual AMF process, into the high fat tank. 

This process variant combines two big advantages, first a separate cooling after secondary skimming and hence also separate availability of the beta serum that exhibits a particularly high content of phospholipids and is therefore an ideal basis for special products. Second, the separate secondary skimming relieves the strain on the actual cream concentrator with the result that a smaller machine type can be used for the same oil capacity or, in the case of existing plants, a higher oil capacity can be achieved by retrofitting secondary skimming. 

The alpha serum is not admixed with the beta serum in this process and therefore has a very small content of phospholipids in comparison to the standard process. By this means, the use of the serum can be compared with the possibilities of a skim milk; it must however be noted that the fat content is slightly higher compared to a skim milk since a certain proportion of the fat passes into the serum phase when concentrating the cream.

Process with Butter

With butter as the initial product, the emulsion of water in oil is already present. Partial phase inversion will have taken place during the churning process. The initial product is of decisive importance for the design of the installation. Basically, an installation for processing cream is also suitable for the separation of melted butter.

Sweet cream butter

When sweet cream butter with a pH of around 6.5 is to be processed and no “chemical agents” (e.g. citric acid) are allowed to be used for denaturing the proteins, the emulsion layer has to be taken into account.

Centrifugation and destruction of this layer can only be carried out by specially designed separators and phase inversion. The operating method of the separator has a decisive influence on the process, the required additional equipment and the efficiency of the installation. For processing sweet cream butter, it is necessary to use a separator which allows concentration to 99.5 percent fat. The emulsion has to be discharged with the serum phase.

The melted butter, e.g. melted with the BXA, is generally pumped directly into the high fat tank. The butter blocks are taken from cold storage at, for instance -20 °C, and are melted in the melting system. The product temperature in the buffer tank, depending on the design of the plant, is between 45 and 65 °C. The temperature of the product is raised to 70 – 75 °C in a plate heat exchanger. 

Phase inversion by means of a homogenizer is required to minimise the emulsion phase. The oil concentrator achieves separation of 99 percent fat. The heavy phase, a mixture of butter milk and residual emulsion particles, is fed to a skimming separator.

The oil phase (light phase) is heated to about 90 °C and then separated again in a further separator. Before the oil is fed to the polishing separator, wash water is added to improve the quality of the oil.

The further process steps are comparable with those of the processes already described. Since no cream concentrator is present, secondary skimming of the serum phase after the oil concentrator is highly recommended. When sour cream butter with a pH of 4.6 to 4.5 and with an increased protein content is to be processed, a decanter can be used. Separate concentration of the solids is possible.

In any case, a separator (polishing separator) has to be installed downstream to increase the fat concentration to 99.5 percent.

Salted butter

The amount of salted butter used as a raw material for the production of butter oil in recent years has risen steadily. The salt content is removed together with the butter milk during centrifugal separation. The salt concentration in the butter milk increases to approx. 10 percent if the original salt content of the butter was 2 percent for example.  Further processing of the salted butter milk is limited.

The emulsion phase in salted sweet cream butter can also be “broken” by the addition of citric acid. At the same time, the protein in the butter is denatured. Thetreated raw material then behaves in the same way as sour cream butter.

The melted butter is brought to a pH of 4.5 – 4.6 by the addition of acid. At this pH, not only the free protein is denatured; in addition, due to the alteration in the intact fat-globule membrane protein, the membrane is broken open and the emulsion is destroyed. An easily decantible sediment is then obtained in addition to a clear water and oil phase. In contrast to “real” sour cream butter, this sediment content is significantly lower. One reason is that the fat-free dry matter (part of which consists of protein) is less in the case of sweet cream butter than is the case with sour cream butter.

Special Processes / Special Solutions

In addition to the processes described, special solutions are required in some areas to meet all demands.

Batch process

If only small quantities of cream have to be processed, a system comprising two separators can be used. Besides the cream separator, only one instead of two oil separators is used.

To be able to produce AMF with this system, the plant must be passed through twice. In the first step / batch, the cream is concentrated, phase inversion is carried out and the oil is concentrated.

This intermediate product is stored in a large buffer tank. Once this is full, the process is interrupted and prepared for the second batch / step, without processing fresh cream.

In the following step, the previously concentrated oil is subjected to the same process steps as the raw product before. The cream heater from the first step is utilized to heat the oil to 90 °C. 

The previously used oil concentrator is used as a polisher in the second step and the intermediate product from the first step is upgraded and achieves AMF quality.

The further steps can be compared with those of the original process.

Ghee production

Process line for Ghee

Ghee, which is also known as clarified butter, is one of the most important fats in many regions, including applications in the Indian, Pakistani and African cuisines.

If Ghee is to be produced, the proteins must remain as long as possible in the product in contrast to AMF,and be treated thermally in such a way that the desired taste is attained.

The classic method is to heat and boil butter or cream with fire in so-called boiling pans until all the water has evaporated and the protein simultaneously “burns” and denatures.

The sediment is subsequently separated and the fat phase used as Ghee.

To make this process more efficient and faster, simple separators in combination with hydrocyclones can be used. After melting the butter and evaporating the water, the prepared product is separated from the solids in a clarifier and the upstream cyclone and achieves a high level of purity in the process.

Intermediate steps such as sedimentation are dispensed withe so that existing cooking pans can be used substantially more efficiently.