CN110167363B

CN110167363B - Steam heating of nuts by forced convection with preheating

Info

Publication number: CN110167363B
Application number: CN201880006271.4A
Authority: CN
Inventors: J·F·科瓦克斯; J·M·拉佩尔三世; M·V·斯克拉菲尼
Original assignee: Laitram LLC
Current assignee: Laitram LLC
Priority date: 2017-01-10
Filing date: 2018-01-05
Publication date: 2022-06-03
Anticipated expiration: 2038-01-05
Also published as: AU2018208302B2; WO2018132307A1; CN110167363A; AU2018208302A1; AU2022100141B4; ZA201904189B; AU2022100141A4; ES2724365R1; ES2724365A2; ES2724365B2

Abstract

A process for pasteurizing almonds and other nuts using steam at atmospheric pressure. The amount of condensation on the nuts and subsequent water uptake is limited by pasteurizing the nuts in a heating chamber having a gas atmosphere comprising a steam mixture and creating a forced convection path through the nuts. The limited water uptake preserves the quality of the nuts. A forced convection steam cooker that transports food product on a porous conveyor belt forces a steam mixture through the nuts. The preheater preheats the nuts so that they can be pasteurized in a steam cooker at a temperature of 85 ℃ to 99 ℃, thereby reducing residence time and improving processing.

Description

Steam heating of nuts by forced convection with preheating

Technical Field

The present invention relates generally to steam cooking and more particularly to a method of steam heating nuts using forced convection at temperatures below 100 ℃ (212 ° f).

Background

Nuts, such as almonds, are often pasteurized by immersion in a hot water or air-steam environment. Steam sterilizers typically use the heat of condensation to heat the outer surfaces of the nuts to a temperature high enough to inactivate enough microorganisms to achieve an acceptable level of pasteurization. The nuts enter the steam pasteurizer at a temperature below the steam temperature. The steam condenses on the outer surface of the nuts and raises their temperature. However, the clumping loosens and loosens the nut shell. If apricots and other nuts are sold with a skin, the amount of water absorbed by the nuts should be limited. One method of limiting coagulation in almonds is described in international patent publication No. wo 2013/171336. This document teaches preheating low moisture food to a temperature above or slightly below the condensation temperature of the water vapour in the heating chamber to limit condensation. Another method described in U.S. patent application publication No.2013/0040030 applies steam to nuts at a pressure below atmospheric pressure to limit water absorption. However, preheating requires an additional heater, and the vacuum system requires batch processing, rather than continuous processing.

Disclosure of Invention

One version of a method for pasteurizing nuts embodying features of the invention comprises: (a) transporting the nuts along a transport path through a preheating chamber; (b) transporting nuts preheated in said preheating chamber along a transport path through a heating chamber; (c) forcing a substantially uniform gaseous atmosphere comprising a vapor mixture through the nuts in the heating chamber along a connecting path intersecting the transport path to heat the skins of the nuts and limit the amount of water condensation around the nuts; (d) maintaining atmospheric pressure in the heating chamber; and (e) controlling the temperature of the gaseous atmosphere in the heating chamber to a heating temperature greater than 85 ℃ and less than 99 ℃ to pasteurize the nuts.

Drawings

These features and aspects of the present invention, as well as its advantages, are described in more detail in the following description, appended claims, and accompanying drawings, in which:

FIG. 1 is a side view of a portion of a steam cooker embodying features of the invention with the side wall of the steam cooker facing away for clarity; and

FIG. 2 is an axial cross-sectional view of the steam cooker of FIG. 1;

FIG. 3 is a side cross-sectional view of the steam cooker of FIG. 1; and

fig. 4 is a block diagram of the steam cooker with the preheating zone shown in fig. 1.

Detailed Description

In fig. 1, a steam cooker embodying and characterizing features of the invention is shown, with its parts removed to better illustrate the side walls of the steam cooker facing. The environmentally-open cooker 14 has an outer shell 16, which outer shell 16 is supported on legs 17 and extends from an inlet end 18 to an outlet end 19. The foraminous conveyor belt 20 is trained about drive and

idler sprockets

22, 23 located at opposite ends of an upper carry way 24 through the cooker. Turning rollers or drums 26 guide the endless loop along a return path 28 below the cooker. A steam pipe network 30 injects steam supplied from a boiler or other steam source into the cooker through the bottom of the enclosure. The injection of steam is regulated by a valve 31 (in fig. 2) in the steam network.

The cooking apparatus shown is modular, with at least two identical heating modules 32, 32'. More modules may be connected in series to extend the total low temperature heating zone. A single module may be used for food products requiring only a short heating time. Each module is controlled individually by its own steam valve. A controller, such as a programmable logic controller, uses feedback signals from the temperature sensing probes 34 in each heating module to control the opening of the steam injector valves to maintain a predetermined heating temperature in each module. The probes, controllers and valves provide a means of maintaining a preselected temperature in each module. As also shown in FIG. 2, an air circulator (e.g., a fan 36 or blower) draws air 37 into the cooking vessel through one of the side walls 38. The fan also draws the steam 40 injected into the cooker through openings in an air chamber 42, where the air and steam mix 42. A fan blows the air-vapor mixture through an opening in the top of the plenum. The air-steam mixture then circulates along a convective path, as indicated by arrow 44, which intersects nuts 46 being conveyed along the carryway atop the conveyor belt 20. The conveyor belt is porous to allow the air-steam mixture to pass through and also to allow any condensate to drain. Other features of such forced convection cookers described so far are given in us patent No.6,274,188, 8/14/2001, incorporated herein by reference, for "a method for steam cooking low temperature prawns to reduce yield loss". An example of such a cooking appliance is the Laitram machine by Hara, Louisiana, USAManufactured and sold by inc

Provided is a cooking device. Due to the thoroughness of the forced convection heat treatment, the heat treatment can be carried out at temperatures below 100 ℃ (212 ° f) at atmospheric pressure. Indeed, the temperature of the heated zone below 85 ℃ (185 ° f) and preferably in the range of 62 ℃ (144 ° f) to 79 ℃ (175 ° f) can effectively blanch or pasteurize almonds without blistering or sagging their skins, as the low temperature can minimize moisture absorption by almonds.

In operation, nuts such as peanuts or almonds and other woody nuts are conveyed by the conveyor belt 20 along the conveying path 56 into the steam cooker 14. The nuts are heated in a low temperature cooking zone 58, which low temperature cooking zone 58 may include one or more identical forced convection heating modules 32, 32'. Air is drawn into the module and mixed with steam to form a substantially uniform gaseous atmosphere of air (or other gas, such as nitrogen) and steam or water vapor. The steam mixture is circulated by an air circulator (e.g., a fan) in a convective path that intersects the food product. In this example, the convection path is perpendicular to the conveyance path 56, but it may intersect or intersect the conveyance path from other directions. Together with the low temperature heat treatment, the forced convection flow through the nuts shears the coagulum that wraps around the nuts and inhibits moisture absorption. The duration of heating (dwell time) is set by one or more of the following: (a) the length of the low temperature heating zone 58, (b) the speed of the conveyor 20, (c) the temperature of the heating zone, (d) the size and type of nuts, and (e) the thickness of the nut mat on the conveyor. For almonds, the residence time may be 4 to 9 minutes in order to achieve a sufficient lethality, e.g. a 6 log reduction of the target organism (e.g. salmonella). The temperature of the heating zones is measured by temperature probes and controlled by the amount of steam introduced into the cooker in each module.

Fig. 3 shows a steam cooker 14 with two heating modules 32, 32'. In the first module 32, the convective path through the porous conveyor belt 20 and the conveyed nuts 46 is downward. In the second module 32', the convection path is upward through the nuts. Subjecting nuts or other food products to upward and downward convective flow results in a more uniform heat treatment.

The low temperature pasteurization as described above effectively minimizes the detrimental absorption of water by the nuts. However, pasteurization of nuts at lower temperatures requires longer residence times in the cooker to achieve the desired pathogen kill. While longer residence times reduce product throughput.

As shown in fig. 4, preheating the nuts in a low-moisture dry air preheating chamber 60 or preheater prior to delivery into the pasteurization zone 62 reduces moisture absorption during subsequent pasteurization at higher temperatures (e.g., temperatures between 90 ℃ (194 ° f) and 99 ℃ (210 ° f), rather than temperatures below 85 ℃ (185 ° f)). For example, nuts with a surface temperature pre-heated to about 54 ℃ (130 ° f) at a relative humidity between 1% and about 60% may be pasteurized for only 1.75 minutes at 95 ℃ (203 ° f) rather than at 79 ℃ (175 ° f) for 4 minutes in a low temperature pasteurization zone. The preheater heats the surface of the nuts to a temperature below the dew point or condensing temperature to ensure that a coagulum forms on the outer surface of the nuts during pasteurization. Tests have shown that by preheating the nuts in a preheater 60 at a temperature between about 57 ℃ (135 ° f) and about 85 ℃ (185 ° f) for about 1 minute to about 6 minutes to raise the surface temperature of the nuts to between about 38 ℃ (100 ° f) and about 70 ℃ (158 ° f), the nuts can be pasteurized in a forced convection steam pasteurization zone 62 of a cooker at a temperature between 85 ℃ (185 ° f) and 99 ℃ (210 ° f) for a residence time of about 1 minute to about 6 minutes. This reduced pasteurization time increases throughput. Pasteurization can also be carried out at temperatures as low as 74 ℃ (165 ° f) with longer residence times.

Although the preheating chamber 60 has been described as a low humidity dry heat heater, in other versions the preheating chamber 60 may be a separate forced convection steam cooker, an additional forced convection heating module before the two modules 32, 32' of fig. 1, or the first module 32 of fig. 1.

Claims

1. A method of pasteurizing nuts, comprising:

conveying the nuts along a conveying path through a preheating chamber;

transporting nuts preheated in said preheating chamber through a heating chamber atop a foraminous conveyor belt traveling along a transport path;

wherein the pre-heating chamber pre-heats the nuts to a surface temperature below a condensation temperature in the heating chamber such that condensation forms on the nuts located in the heating chamber;

forcing a substantially uniform gaseous atmosphere comprising a mixture of steam along a downward forced convection path through the nuts and the porous conveyor belt in the heating chamber to heat the skin of the nuts by condensation, but to limit the amount of condensation around the nuts to prevent the skin from bubbling or relaxing;

maintaining atmospheric pressure in the heating chamber;

controlling the temperature of the gaseous atmosphere in the heating chamber to a heating temperature greater than 85 ℃ and less than 99 ℃ to pasteurize the nuts.

2. The method of claim 1, wherein the temperature of the preheating chamber is between 57 ℃ and 85 ℃.

3. The method of claim 1 wherein said nuts have a residence time in said preheating chamber of between 1 minute and 6 minutes.

4. The method of claim 1 wherein said preheating chamber preheats said nuts to a surface temperature between 38 ℃ and 85 ℃.

5. The method of claim 4 wherein said preheating chamber preheats said nuts to a surface temperature of less than 70 ℃.

6. The method of claim 1 wherein said nuts have a residence time in said heating chamber of between 1 minute and 6 minutes.

7. The method of claim 6 wherein said nuts have a residence time in said heating chamber of 4 minutes or less.

8. The method of claim 1, wherein the pre-heating chamber is a low humidity dry air pre-heater having a relative humidity maintained between 1% and 60%.

9. The method of claim 1, wherein said preheating chamber is a forced convection steam cooker.

10. The method of claim 1, wherein said nuts are almonds having a skin.