GB1605159A

GB1605159A - Vacuum cooling

Info

Publication number: GB1605159A
Application number: GB1435880A
Authority: GB
Original assignee: Tweedy of Burnley Ltd
Current assignee: Tweedy of Burnley Ltd
Priority date: 1978-05-12
Filing date: 1978-05-12
Publication date: 1982-07-14

Description

(54) IMPROVEMENTS RELATING TO VACUUM COOLING (71) We, TWEEDY OF BURNLEY LIMITED, of Peel Mill, Gannow Lane, Burnley in the County of Lancaster, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method of vacuum cooling moisture-containing foodstuff articles and includes apparatus for carrying out the method. The invention relates particularly to a method and apparatus for controlling rates of vacuum cooling.

Moisture-containing foodstuff articles can be cooled by subjecting the articles to reduced pressures, such that the moisture in the articles evaporates, the latent heat of evaporation being removed from the articles. In particular, this method can be used to cool baked farinaceous products such as bread and pie crusts. Vacuum cooling of foodstuff articles is attractive because it allows the temperature to be reduced quicker than is possible by the traditional method of simply allowing the articles to cool under atmospheric pressure, and it also ensures that the articles are in a controlled atmosphere during cooling which avoids certain disadvantages (e.g. spore growth) of the traditional atmospheric cooling.

However, it is sometimes difficult to carry out vacuum cooling of foodstuff articles without detracting from the desired characteristics of the finished articles. For example, if the article is of a type which will easily distort, too rapid cooling will spoil the article, or even cause it to explode, whilst ori the other hand if the cooling is too slow, then a thick hard crust may form on the article.

In the Specification of United Kingdom Patent No: 1 413 481 a method of exercising control over the rate of cooling of farinaceous foodstuff articles by vacuum is described. The present invention provides a method of exercising control over a vacuum cooling process, which may be used in conjunction with the method described in Patent Specification No: 1 413 481 but it is to be understood that the invention can also be used in instances where the method of that patent is not employed.

According to a first aspect of the invention a method of cooling a moisture containing foodstuff article comprises: placing the article in a sealed chamber connected to a pump by a pipe and a valve, operating the pump continuously to reduce the pressure in the sealed chamber so that moisture vapour is given off by the article, whereby the latent heat of evaporation of the vapour is removed from the article, and progressively opening the valve in stepwise manner to reduce the impendence in the pumping system.

According to a second aspect of the invention a cooling apparatus for the treatment of moisture-containing foodstuff articles comprises a vacuum chamber to receive the article(s) to be cooled; a pumping system comprising a pump, and a pipe and a valve connecting the pump to the vacuum chamber; and a pre-programmed control system for progressively opening the valve in stepwise manner to reduce the impedence in the pumping system. There may be a motor drivingly connected to the valve, the control system including a timer, the output signals from which cause operation of the motor, the timer being pre-programmed to issue a series of output signals of predetermined duration and frequency.

One construction of apparatus in accordance with the invention and its method of operation, will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a partly sectioned and somewhat diagrammatic front elevation of a vacuum cooling apparatus, and Figure 2 is a section through a valve assembly.

In order to speed up the distribution and sale of loaves of bread after baking, it is necessary to cool the loaves rapidly prior to their being packaged. The process of vacuum cooling in which loaves are placed in a sealed chamber and pressure in the container is reduced, suggests itself as a means of rapidly cooling loaves.

However, if the pressure in the container is reduced too quickly, the resulting rapid escape of the moisture from within the loaves can cause destructive deformation or even explosion of the loaves. In an attempt to overcome this problem the process of vacuum cooling has to be modulated in some instances, such as by the use of the method described in United Kingdom Patent Specification No: 1 413 481. In the embodiment of the invention described with reference to the accompanying drawings a modulated vacuum process for the cooling of loaves of bread is regulated by altering the impedence of a pumping system.

Referring to Figure 1 of the drawings, a chamber for use in a modulated vacuum cooling process for cooling loaves is indicated generally at 10 and takes the form of a sealed pressure vessel. The cooling process for which the apparatus is designed operates on a batch system, and the chamber 10 is large enough to receive a portable rack 12 which itself supports shelves 13 on which loaves 14 of bread, such as rye bread are carried.

A pair of pipes 18 and 19 connects the inside of the chamber 10 with a vacuum pump 20 driven by a motor 22, the pipe 19 being arranged in parallel with part of the pipe 18. The pipe 18 in this particular example is of approximately 30 centimetres diameter bore and the pipe 19 which provides a by-pass for the pipe 18 is of approximately 2.5 centimetres diameter bore.

The pump 20 and the motor 22 are mounted on a base plate 23 adjacent to the chamber 10.

Operation of the motor 22 causes the pump 20 to evacuate the chamber 10 via either or both of the pipes 18 and 19, and the motor 22, pump 20 and pipes 18 and 19 together form a pumping system for the apparatus. In order that the impedence of the pipes 18 and 19 (and therefore the impedence ofthe pumping system) can be varied, a valve 24 is provided in the pipe 18 and a valve 25 is provided in the pipe 19.

Since the motor 22 operates at constant speed and the pump 20 has a fixed capacity, the pumping rate of the pumping system can only be varied by altering the impedence of the system, and the pumping rate is inversely proportional to the impedence.

An electrical control panel 26 is mounted on one side of the chamber 10 and house control apparatus (not shown) required to control the modulated vacuum cooling of the loaves 14 within the chamber 10 by controlling the operation of the motor 22 and the valves 24 and 25.

The valve 25 is a solenoid controlled on/off valve so that the pipe 19 can be either opened or closed under the control of the electrical control apparatus. The valve 24 on the other hand is a butterfly valve (shown more clearly in Figure 2) and having a valve member 40 carried by a spindle 42 which is journalled in the valve body 41, which is itself fixed in the pipe 18.

When closed, the valve 24 completely shuts off the pipe 18 and when fully opened, it permits virtually unimpeded flow through the pipe 18.

A small electric motor 44 is connected to the valve spindle 42 via a speed reduction gearbox 46 which has a high velocity ratio, and may for example, be a double-reduction worm gear unit.

The reduction gearbox 46 is mounted on the valve body 41 and the motor 44 is mounted on the gearbox.

Operation of the motor 44 in one direction causes opening of the valve 24, and operation of the motor in the reverse direction causes closing of the valve 24. Because of the large speed reduction it is necessary to operate the motor for a protracted period (for example 40 seconds) in order to turn the valve member 24 through 90" from the fully closed to the fully opened position.

A detection apparatus 16 is provided and as shown in Figure 1, this apparatus is mounted within the chamber 10 adjacent to the inlet to the large diameter pipe 18. It is the function of the detection apparatus to control the application of the vacuum within the chamber 10 to avoid distortion or explosion of the loaves 14, and the detection apparatus is fully described in the specification of Patent Application No: 19104/78 from which this application is divided.

Included in the electrical control panel 26 is an electronic timer of known construction, which can be pre-programmed to give signals of predetermined duration and frequency, and this timer is arranged to cause operation of the motor 44 in a forward sense each time it produces a signal.

The operation of the apparatus will now be described. At the start of the modulated vacuum cooling process, the loaves 14 which have been baked (and which may have been partially cooled) are loaded on to the shelves 13 of the rack 12. The rack 12 is inserted into the chamber 10, and when the door of the chamber is moved towards the closed position, part of the detection apparatus 16 is lowered on to the loaves 14 as described in the specification of Application No: 19104/78. The cooling cycle is initiated by operation of a switch (not shown) and this causes the motor 22 to be operated to drive the pump 20 (and the pumping is then continuously operated until shut down of the apparatus) but at this stage in the process, the valve 24 in the pipe 18 is closed, and the valve 25 in the by-pass 19 is opened, so that there is a considerable impedence in the connection between the pump and the chamber 10. Air is withdrawn from the chamber 10 until the pressure in the chamber falls to a level equal or just above the saturated vapour pressure of water at the temperature of the loaves. A pressure responsive switch (not shown) in the chamber 10 is pre-set to signal the attainment of the critical pressure, and the signal from this switch causes the motor 44 to be operated in a forward sense by the timer, at the pre-programmed rate, for example for one half second every fifteen seconds, and consequently the valve member 40 of the butterfly valve 24 is progressively opened in a stepwise fashion. This opening of the valve 24 begins to reduce the impedence of the pumping system.

Once the pressure within the chamber 10 is reduced below that of the saturated vapour pressure of the moisture within the loaves 14, the moisture begins to evaporate quite rapidly from the loaves which begin wo swell upwardly If the pressure is reduced too quickly, the loaves 14 tend to swell so quickly thst they are liable to be distorted or even to explode. However, as soon as the upward expansion of the loaves is sufficient to operate a sensing switch in the detecting apparatus 16, the control circuit of the motor 44 is opened so that even though the timer continues to issue signals, there is no corresponding energisation of the valve motor 44 and the valve 24 remains in its partially opened position. Hence, the impedence in the pumping system remains unaltered, and the pressure/time curve of the atmosphere in the chamber 10 from then on takes the form of the hyperbola which occurs when the pumping rate is not modulated. This slows the cooling process.

If the loaves 14 actually shrink as a result of slowing the cooling process, the detecting apparatus 16 senses this and the sensing switch in that apparatus is again opened and this re-connects the valve motor 44 to the timer for further opening of the valve 24.

If the upper loaves 14 rise so rapidly that an emergency switch in the detecting apparatus is closed, then that changes the state of the control circuit and over-rides the timer, switching the motor 44 into reverse, and operating that motor in a continuous fashion. Thus, the valve 24 commences to close, producing an increase in the impedence in the pipe 18. At the same time, a solenoid controlled valve 72 is opened to admit a restricted flow of air into the chamber 10. Once the excessive swelling of the loaves had been counteracted, and they begin to shrink again, the emergency switch opens, so that the reverse operation of the motor 44 stops. On further shrinkage of the loaves, when the sensing switch is closed, the timer is re-connected with the valve motor 44 so that the valve 24 is again progressively opened to decrease the impedence and increase the vacuum in the chamber 10.

This control process comprising the steps of operating the sensing switch, and perhaps the emergency switch may be repeated during the cooling process, and takes place quite automatically.

Although the control circuit is generally capable of exerting control over the process of modulated vacuum cooling carried out in the chamber 10 by pre-programming of the timer, the control circuit can and does receive information from the detection means 16 in the form of signals. The modulated vacuum cooling process carried out in the chamber 10 is thus not merely a pre-programmed automatically controlled process but may, when the situation demands, be subjected to a degree of feedback control arising from operation of the detection means 16 which is arranged to detect changes in the height of the loaves 14 and to give ares- ponse to those changes in the form of a signal (or no signal) to the control panel and the control circuit which then exercises control of the valve motor 44, and the valves 24,25 and 72 accordingly.

The electrical control circuit further includes a pressure responsive switch (not shown) located in the chamber 10 and pre-set to operate when a predetermined low pressure, slightly higher than the pressure at which the cooling process is to be terminated, is attained. When this switch is activated, a cycle end timer is started, but the valve 24 continues to open (or to remain in a partially open state if the sensing switch is held open). During the period of operation of the end timer (say about 30 seconds) the pressure in the chamber varies very little because the pressure/time curve is then following a near horizontal path. (In a typical example, the pressure reduces from 9 TORR to 5 TORR).

During the period that the cycle end timer is operating, the internal pressure is equalising across each loaf of bread, and this is desirable to prevent distortion of the loaves when the pressure in the chamber increases.

At the end of the time delay, the motor 44 is switched into continuous reverse operation, and at the same time the valve 72 is opened, so that the impedence in the pumping system increases and some air is admitted into the chamber. The pressure in the chamber begins to rise slowly, and when a predetermined safe pressure is attained a pressure responsive switch operates the valve 70 and allows a full flow of air into the chamber. It is then possible to open the door of the chamber and remove the rack 12 within the loaves 14, and the cooling cycle is complete.

WHAT WE CLAIM IS: 1. A method of cooling a moisture-containing foodstuff article comprising: placing the article in a sealed chamber connected to a pump by a pipe and a valve; operating the pump continuously to reduce the pressure in the sealed chamber so that moisture vapour is given off by the article, whereby the latent heat of evaporation of the vapour is removed from the article, and progressively opening the valve in stepwise manner to reduce the impedence in the pumping system.

2. A cooling apparatus for the treatment of moisture-containing foodstuff articles, comprising: a vacuum chamber to receive the article(s) to be cooled; a pumping system comprising a pump, and a pipe and a valve connecting the pump to the vacuum chamber and a pre-programmed control system for progressively opening the valve in a stepwisemanner to reduce the impedence in the pumping system.

3. A cooling apparatus as claimed in Claim 2, in which there is a motor drivingly connected to the valve, the control system including a timer, the output signals from which cause operation of the motor, the timer being preprogrammed to issue a series of output signals of predetermined duration and frequency.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

14 tend to swell so quickly thst they are liable to be distorted or even to explode. However, as soon as the upward expansion of the loaves is sufficient to operate a sensing switch in the detecting apparatus 16, the control circuit of the motor 44 is opened so that even though the timer continues to issue signals, there is no corresponding energisation of the valve motor 44 and the valve 24 remains in its partially opened position. Hence, the impedence in the pumping system remains unaltered, and the pressure/time curve of the atmosphere in the chamber 10 from then on takes the form of the hyperbola which occurs when the pumping rate is not modulated. This slows the cooling process.

If the loaves 14 actually shrink as a result of slowing the cooling process, the detecting apparatus 16 senses this and the sensing switch in that apparatus is again opened and this re-connects the valve motor 44 to the timer for further opening of the valve 24.

If the upper loaves 14 rise so rapidly that an emergency switch in the detecting apparatus is closed, then that changes the state of the control circuit and over-rides the timer, switching the motor 44 into reverse, and operating that motor in a continuous fashion. Thus, the valve 24 commences to close, producing an increase in the impedence in the pipe 18. At the same time, a solenoid controlled valve 72 is opened to admit a restricted flow of air into the chamber 10. Once the excessive swelling of the loaves had been counteracted, and they begin to shrink again, the emergency switch opens, so that the reverse operation of the motor 44 stops. On further shrinkage of the loaves, when the sensing switch is closed, the timer is re-connected with the valve motor 44 so that the valve 24 is again progressively opened to decrease the impedence and increase the vacuum in the chamber 10.

This control process comprising the steps of operating the sensing switch, and perhaps the emergency switch may be repeated during the cooling process, and takes place quite automatically.

Although the control circuit is generally capable of exerting control over the process of modulated vacuum cooling carried out in the chamber 10 by pre-programming of the timer, the control circuit can and does receive information from the detection means 16 in the form of signals. The modulated vacuum cooling process carried out in the chamber 10 is thus not merely a pre-programmed automatically controlled process but may, when the situation demands, be subjected to a degree of feedback control arising from operation of the detection means 16 which is arranged to detect changes in the height of the loaves 14 and to give ares- ponse to those changes in the form of a signal (or no signal) to the control panel and the control circuit which then exercises control of the valve motor 44, and the valves 24,25 and 72 accordingly.

The electrical control circuit further includes a pressure responsive switch (not shown) located in the chamber 10 and pre-set to operate when a predetermined low pressure, slightly higher than the pressure at which the cooling process is to be terminated, is attained. When this switch is activated, a cycle end timer is started, but the valve 24 continues to open (or to remain in a partially open state if the sensing switch is held open). During the period of operation of the end timer (say about 30 seconds) the pressure in the chamber varies very little because the pressure/time curve is then following a near horizontal path. (In a typical example, the pressure reduces from 9 TORR to 5 TORR).

During the period that the cycle end timer is operating, the internal pressure is equalising across each loaf of bread, and this is desirable to prevent distortion of the loaves when the pressure in the chamber increases.

At the end of the time delay, the motor 44 is switched into continuous reverse operation, and at the same time the valve 72 is opened, so that the impedence in the pumping system increases and some air is admitted into the chamber. The pressure in the chamber begins to rise slowly, and when a predetermined safe pressure is attained a pressure responsive switch operates the valve 70 and allows a full flow of air into the chamber. It is then possible to open the door of the chamber and remove the rack 12 within the loaves 14, and the cooling cycle is complete.

WHAT WE CLAIM IS: 1. A method of cooling a moisture-containing foodstuff article comprising: placing the article in a sealed chamber connected to a pump by a pipe and a valve; operating the pump continuously to reduce the pressure in the sealed chamber so that moisture vapour is given off by the article, whereby the latent heat of evaporation of the vapour is removed from the article, and progressively opening the valve in stepwise manner to reduce the impedence in the pumping system.
2. A cooling apparatus for the treatment of moisture-containing foodstuff articles, comprising: a vacuum chamber to receive the article(s) to be cooled; a pumping system comprising a pump, and a pipe and a valve connecting the pump to the vacuum chamber and a pre-programmed control system for progressively opening the valve in a stepwisemanner to reduce the impedence in the pumping system.
3. A cooling apparatus as claimed in Claim 2, in which there is a motor drivingly connected to the valve, the control system including a timer, the output signals from which cause operation of the motor, the timer being preprogrammed to issue a series of output signals of predetermined duration and frequency.