PLANT FOR TEMPERATURE-CONTROLLED TREATMENT OF FOOD PRODUCTS, SUCH AS MILK OR THE LIKE

Field of the invention

The present invention generally finds application in the field of food industry systems and particularly relates to a plant for temperature-controlled processing of liquid or semi-liquid food products, such as milk, pulps, sauces, jams or the like.

Background of the invention

Food products, particularly liquid or semi-liquid products, are known to require certain heat treatments for partial or total destruction of the microbial load, to extend products' shelf life.

Such processes stabilize the microbial count for a time that depends on the specific type of treatment, i.e. essentially on the selected time-to-temperature ratio.

On the one hand, a higher temperature is more effective in destroying the microbial flora, on the other hand an excessively long treatment time would tend to degrade most of the nutrients in the product, thereby reducing its organoleptic quality. Thus, treatment times and temperatures have to be mutually adjusted to meet the combined need of obtaining a high quality product with an adequate shelf life.

An exemplary know milk sterilization plant is diagrammatically shown in FIG. 1. The plant essentially comprises a tank A, wherefrom the liquid is drawn at a storage temperature Ti of about 4°C, a preheating section B, in which milk is progressively heated to temperatures T ₂ and T ₃ of about 75 ⁰ C and 85°C respectively, by steam flows Si and S ₂ , a unit C for destroying the microbial load, in which milk is heated to a sterilization temperature T ₄ of about 15O ⁰ C by flow S3, a section D for progressively cooling milk from temperature T ₄ to temperatures T ₅

and T ₆ and a storage tank for the treated milk E.

Particularly, the microbial load destroying unit C may be of the direct type, providing injection of steam S ₃ in milk. A flash vaporization unit F, operating by abrupt expansion, is provided upstream of unit C to separate steam from milk. In this unit, the milk added with the steam flow S ₃ is subjected to quasi instantaneous expansion, thereby generating a steam flow Si at temperature T _5v , whose latent heat is at least partly also used to preheat the milk in section B, and a flow of "concentrated" milk, cooled to a temperature T ₅ of about 80 ⁰ C. To inhibit separation of milk components after such abrupt expansion, a homogenization unit G is provided downstream of the expansion unit.

While this kind of system has been improved with time to obtain an end product of high organoleptic quality, because direct steam injection can heat milk to the sterilization temperature in a very short time, it still suffers from a few recognized drawbacks.

Firstly, vacuum expansion inevitably causes the loss of many volatile nutrients, such as aromatic nutrients, thereby affecting the end quality of the processed product.

Furthermore, direct contact with milk requires steam to be pretreated to ensure it is as aseptic as possible when it is injected. This process is highly inconvenient and costly. As is known, extraction of all chemical, physical and pathological residues from a gas flow requires highly complex implementations, and the relevant national and international standards are frequently updated, thereby involving higher costs.

Finally, due to the presence of steam in milk, the flash expansion unit F is required to operate under vacuum, so that steam may be almost totally separated from the liquid. As a result, the homogenization step that is always required after such treatments, shall be carried out under high pressure and under aseptic conditions,

i.e. by preventing the milk flow from contacting any external pathogenic agents susceptible of polluting it and of nullifying the benefits of the previous sterilization step.

Due to the irreversible heat losses associated with a system of this type, its thermal efficiency is very low, i.e. of the order of 50%, which makes the system unattractive in terms of cost effectiveness.

Summary of the invention

The main object of this invention is to overcome the aforementioned drawbacks, by providing a system for temperature-controlled processing of food products that is highly efficient and relatively cost-effective.

A particular object of the invention is to provide a system whose end product has an optimal organoleptic quality.

A further object is to provide a system that allows to minimize installation and maintenance costs.

Another object is to provide a system in which such installation and maintenance are of the highest simplicity.

Yet another object of the invention is to provide a method for processing food products that minimizes process costs and provides a high quality end product.

Another important object is to provide a system that has a relatively high efficiency and is attractive in terms of cost effectiveness.

These and other objects, as better explained hereinafter, are fulfilled by a plant for processing food products comprises, in accordance with claim 1 , a storage tank for collecting the product to be processed, a preheating section (3) for causing the

product temperature to increase from an initial storage temperature to an intermediate preheating temperature, a product heat treatment unit downstream of said preheating section for reducing the product microbial load by heating it to a treatment temperature higher than the preheating temperature, a cooling section downstream of said treatment unit, for cooling the product to a final preservation temperature and a hydraulic circuit for providing fluid connection of said storage tank with said cooling section, passing through said preheating section and said heat treatment unit, characterized in that said heat treatment unit comprises quick heating means of the indirect heat transfer and constant flow type, said cooling section comprising instant cooling means including an expansion chamber at a pressure higher than or equal to atmospheric pressure.

Thanks to the particular configuration of the plant according to the invention, the product flowing out of the expansion chamber has a temperature close to the equilibrium temperature corresponding to the pressure in the chamber, so that the processed product will be cooled to a temperature that is higher than the temperature reached by prior art systems.

It shall be understood that the terms "product flowing out" or "outflowing product", as used herein are intended to designate a fluid composed of a liquid fraction and a vapor fraction, which result from abrupt expansion and have substantially the same temperature.

One feature of the plant according to the invention is that, during expansion, the product is subjected to a lower temperature drop than in the prior art plaints, whereby the loss of volatile nutrients in the liquid fraction is reduced, and the organoleptic quality of the processed product is improved.

Advantageously, the hydraulic circuit may include a return line for putting the expansion chamber in fluid communication with the storage tank, so that the volatile substances lost during expansion may be reintroduced in the inflowing product, thereby improving the final quality thereof.

Since the temperature of the fluid after cooling is still relatively high and has a higher enthalpy as compared with prior art plants, heat can be recovered and applied in the preheating step, thereby considerably increasing the overall system efficiency.

In a preferred, non-exclusive embodiment, the preheating section may include a plurality of preheating units to heat the product from the storage temperature to the intermediate preheating temperature. Advantageously, the return line feeds at least partially the heating circuit of one of the preheating units.

The circuit may further have a final line to put the expansion chamber in fluid communication with a processed product preservation tank, situated downstream of the cooling section.

Conveniently, the final branch line may feed at least partially the cooling circuit of one of the preheating units.

This configuration allows to recover heat from liquid and steam flowing out of the chamber, so that the plant of the invention has a thermal efficiency in the range of 80 - 90%.

It shall be understood that the expression quick heating means of the indirect heat transfer and constant flow type, as used herein, is intended to designate heating means in which the product under treatment is not in direct contact with a fluid at higher temperature, e.g. steam, so that the mass flow of the product is substantially constant from the inlet section to the outlet section, except minor product density variations caused by temperature increase. Obviously, mass flow is constant when considering the product as a whole, i.e. as a sum of the liquid and vapor fractions of the inflowing and/or outflowing product.

The use of indirect heating plants, e.g. of the type with heating plates or with a high frequency electromagnetic field provides considerable advantages in terms of

costs and convenience, as no steam treatment and purification arrangements and no aseptically-operating homogenization units is required anymore.

Advantageously, the plant may comprise a product homogenization unit that is included in the preheating section for homogenizing the product upon addition of the steam flow in the storage tank.

Brief description of the drawings

Further features and advantages of the invention will be more apparent from the detailed description of a preferred, non-exclusive embodiment of a plant according to the invention, which is described as a non-limiting example with the help of the annexed drawings, in which:

FIG. 1 is a schematic view of a prior art food processing plant;

FIG. 2 is a schematic view of a food processing plant according to the invention.

Detailed description of a preferred embodiment

Referring to the above figures, the plant of the invention, which is generally designated by numeral 1 , is particularly suitable for processing food products such as milk, purees, fruit juices or the like. While the following description essentially relates to milk processing, it shall be understood that this example is only provided by way of illustration and without limitation, the plant being suitable to process any kind of food product. By analogies, temperature ranges are only provided as a mere example, and do not limit the inventive concept disclosed in the appended claims.

Basically, the plant comprises a milk storage tank 2, a milk preheating section 3, a heat treatment unit 4 located downstream of the latter and designed to reduce microbial load in milk, and a product cooling section 5 downstream of unit 4. The different plant sections are in fluid connection with each other by means of the

hydraulic circuit 6.

In section 3, the product is heated from an initial storage temperature Ti, approximately 4°C, to an intermediate preheating temperature T ₄ of about 80 ⁰ C - 9O ⁰ C. The so preheated milk flows into unit 4 wherein its temperature is abruptly increased to a treatment value T ₅ of about 135°C - 140 ⁰ C. To perform such heating function, this unit comprises quick heating means of the indirect heat transfer and constant flow type, such as either heat exchanger with heating plates of adequate size, a burner or an electromagnetic field application unit.

In the next cooling section 5, milk at temperature T ₅ flows through instant cooling means 7 including an expansion chamber 8 at a pressure P _e higher than or equal to atmospheric pressure so that the product flowing out of such expansion chamber 8 has a temperature Tβ close to the equilibrium temperature corresponding to such pressure P _e . The value of T ₆ is approximately of 100 ⁰ C - 105°C.

As is known, after expansion in chamber 8, the outflowing milk is separated into a liquid fraction L and a vapor fraction V, having the same temperature Tβ, which are both used to preheat the milk flowing into the unit 4.

More in detail, as shown in FIG. 2, the preheating section 3 may comprise a plurality of progressive preheating units 9, 10 and 11. In unit 9, milk is heated from a storage temperature Ti of about 4 ⁰ C to an intermediate temperature T ₂ , typically of about 40 ⁰ C - 50 ⁰ C, using the heat released to such unit 9 by the flow S-i, essentially consisting of the milk vapor phase V.

For this purpose, the line 12 of the circuit 6 feeds the heating circuit of the unit 9 and connects the chamber 8 to the storage tank 2. Thus, the vapor phase V of milk, e.g. having a temperature of 100 ⁰ C to 105 ⁰ C, releases condensation heat to unit 9 through which milk flows coming from tank 2, and increases the temperature of the outflowing milk. The vapor phase V, which is thereby cooled,

will be reintroduced in the storage unit 2.

For properly conveying the vapor phase V, the branch line 12 has the end 13 in the higher portion of the expansion chamber 8. An end of the final line 14 of the circuit 6 is located on the bottom of the chamber 8, for conveying the liquid phase L of milk. This phase, in the same manner as described above for unit 9, is feeding the heating circuit of the preheating unit 10 (flow S ₂ ), to increase milk temperature from the value T ₂ to a value T ₃ of about 70 ⁰ C - 80 ⁰ C.

The liquid phase L, which is thus cooled to a temperature T ₇ of about 40 ⁰ C - 50 ⁰ C, will be cooled to a final preservation temperature T ₈ , which may be the same as the initial storage temperature, i.e. 4°C, by the flow S ₄ in the final cooling unit 15. Milk will be preserved in a tank 16 at this temperature.

In order to homogenize the milk flowing into the unit 4, a product homogenization unit 17 is provided in the preheating section 3, to remove any inhomogeneity in the milk flowing out of the tank 2 due to the addition of the vapor phase V therein.

To heat milk from the temperature T ₃ to the temperature T ₄ , the third preheating unit releases the required heat to the milk by the external flow S ₃ .

The above disclosure clearly shows that the system of the invention fulfills the intended objects and particularly the object of providing a system whose end product has an optimized organoleptic quality.

Thanks to the combination of quick heating means of the indirect heat transfer and constant flow type, with instant cooling means 7, the product flowing out of the expansion chamber 8 has a temperature Tβ close to the equilibrium temperature corresponding to the pressure P _e in the chamber, which provides all the advantages mentioned above.

The plant according to the invention is susceptible of a number of changes and

variants falling within the inventive concept as disclosed in the appended claims. All the details thereof may be replaced by other technically equivalent parts, and the materials may vary depending on different needs, without departure from the scope of the invention.

While the system has been described with particular reference to the accompanying figures, the numerals referred to in the disclosure and claims are only used for the sake of a better intelligibility of the invention and shall not be intended to limit the claimed scope in any manner.