AMF Production Line

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.

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.

Alpha and beta serum secondary skimming

In the process with alpha and beta serum secondary skimming, there is separate skimming of the alpha serum in addition to the skimming of the serum describe before. For this purpose, the serum from the cream concentrator is collected in a balance tank from where it is fed to a further skimming separator so that a further reduction of the serum fat content is realized. The cream produced is fed to the balance tank of the cream concentrator and in this way the fat is processed to butter oil. The serum is in turn used as in the standard process to heat 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.

Acid is added, and the product is heated to a temperature of 70 – 75 °C; an adequate reaction time is then allowed.

The oil is then concentrated in the oil concentrator to approx. 99 percent. The oil is heated to approximately 90 °C in the plate heat exchanger, and it is then concentrated to 99.5 percent in the oil polishing separator. It is necessary to add wash water upstream of the separator so that residual salt particles in solution can be washed out.

Care must be taken to ensure that the pH does not rise again when the wash water is added. The wash water should thus be adjusted to a pH of 4.5 – 4.6 with acid before it is added to the product.

The final value of the oil of 99.8 percent is adjusted in the downstream vacuum evaporator. For processing salted butter, it is extremely important to ensure that all parts of the installation which come into contact with the product are made of special corrosion-proof materials.

Sour cream butter

Sour cream butter is produced from biologically acidified cream. The pH value of the butter is between 4.5 and 5.2 depending on the country of origin.

Processing of sour cream butter into butter oil is generally the least expensive method. This is however only partly true when the pH is between 4.7 and 5.2.

When sour cream butter is processed, a third liquid phase (emulsion phase) is not present, as has already been stated. The most important criterion for the design of the plant is that the separable solids (denatured protein because of the low pH value) can amount to as much as 2 percent absolute. In general, the value is between 1.3 and 1.5 percent DS.

For processing from sour cream butter, it is particularly important to ensure that the melting process in the melting system is gentle, as localized overheating will relatively quickly lead to protein burning. The product leaving the butter melting system at a temperature of 45 – 55 °C is heated in the plate heat exchanger to 70 – 75 °C, and is then pumped to the 3-phase decanter. The oil is concentrated in the decanter to 95 – 98 percent, and is heated to approximately 90 – 95 °C; it is then brought to a concentration of 99.5 percent in the oil polishing separator. The residual moisture content is reduced to less than 0.1 percent by evaporation in the vacuum evaporator. The serum phase generally has a fat content of less than 0.8 percent; accordingly, if we consider the amount obtained (10 – 12 percent of the amount of raw product), fat recovery is only worthwhile if daily quantities are high. The decantible solids are concentrated in the decanter to 20 – 45 percent DS as required, and are then fed from the decanter discharge to the tank. The solids consist mainly of denatured protein. In addition, a fat in DS of 2 – 5 percent must be expected. The oil-enriched heavy phase from the oil polisher is recycled back into the process.

It is necessary to add water upstream of the oil polishing separator in order to ensure optimum “washing out” of the residual protein, and also at the same time to stabilize the separation zone in the bowl of the oil polishing separator in the required position.

For further utilization, the denatured protein discharged by the decanter can be converted into a stable soluble state.

As already mentioned, when butter with high initial FFA values is processed, butter oil can still be obtained by saponification of the short-chain fatty acids, followed by separation of the resulting flocculate.

A suitably prepared wash water (pH > 11) is added to the flow of oil upstream of the oil polishing separator. The free fatty acids come into contact with the basic water, are saponified and are simultaneously washed out. The wash water with the free fatty acids is separated from the oil in the oil polishing separator. The oil leaving the oil polisher then meets IDF standards with respect to FFA values for anhydrous butter oil.

Before “wash water with caustic” is added, the oil must have a concentration of more than 99 percent fat.

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.

Pre-clarification with decanter

For making butter oil, the decanter is used as a machine for pre-concentrating products with a high solids content. So-called Nizo butter is processed into butter oil in Europe. Special cultures are added to the butter during the buttermaking process. This reduces the pH value to approx. 5.2. Aroma cultures are added in order to achieve the required taste. The process of adding the cultures increases the solids content and thus increases the load on the oil concentrator during the oil separation process, as large quantities of denatured solids occur as a result of the low pH value.

Therefore the decanter offers a system that can easily handle the high amount of solids. An oil concentration of 95 – 98 percent is achieved. The solids can be concentrated to approx. 20 – 45 percent DS.

Fractionation

Butter fractionation

The liquid AMF is pumped from the storage tank where the product is stored for further processing in the crystallization tanks where the defined cooling and crystallization takes place. To ensure that the complete fat is liquid a heat exchanger pre-heats the AMF. If necessary this pre-heater can also be used for heating (95 °C) of the oil. In this case, further sections for defined heating and heat recovery would be necessary.

The crystallization tanks are specially designed for their purpose, coils and agitators ensure a very uniform cooling and crystallization of the fat which is the basis for good product quality and highest efficiency.

The separation of the liquid olein and the stearin phase takes place in a nozzle separator. Valves and measurement devices regulate the feed and discharge of the machine.

The liquid olein is discharged by the centripetal pump. The stearin leaves the separator through the nozzles. The olein phase is than heated by a plate heat exchanger to a certain temperature before being transferred into the olein storage tank.

The stearin phase is collected in the hopper of the separator and is transferred by a positive displacement pump through a heating device where all fat is melted again. After this heating stage the liquid fat phase is transferred into the stearin storage tank.

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