The present invention relates to the treatment of cut plant material, in particular to the treatment of cut herbs. Herbs are available for sale in dried form (that is, desiccated form) or in fresh form. Fresh herbs are typically cut in the field, chilled, transported and then packed into plastic film or bags, prior to stocking in a retail environment. It is often found that this sequence of events results in partial dehydration of the fresh herbs, due to the low water vapour pressure in the external environment to which they are exposed. As a result, the consumer of the herbs may perceive a reduction in freshness of the herbs.

Therefore, it is desirable to increase the quality of fresh herbs at the point of consumption, and in particular to reduce the extent of dehydration occurring during processing of the herbs.

Therefore, in a first aspect, the present invention may provide a method of treating cut plant material, comprising the steps of

• providing a quantity of cut plant material;

• exposing the plant material to an atmosphere of at least 90% humidity at a

temperature in the range of 30-60°C.

Preferably, the temperature is less than 55°C, more preferably less than 50°C.

Preferably, the humidity is greater than 95%.

It is thought that this treatment causes water vapour to condense on the surface of the plant material, thus helping to prevent dehydration of the plant material (before treatment, the plant material is stored at a temperature lower than 30°C. For example, it may be held in cold storage at a temperature of around 5°C). The yield of the plant material (that is, the weight of material that is e.g. sold to a consumer) is also increased, due to water being adsorbed or absorbed by the plant material.

It is also thought that the exposure to elevated temperatures and humidity may promote chemical reactions at the surface of the plant material, thus altering important qualities of the plant material, such as taste and aroma. This effect is particularly noticeable in the case of cut herbs (especially woody herbs such as rosemary and thyme), for which this treatment may cause a change in the composition and/or quantity of oils at the surface of the cut herb.

Therefore, the method of the first aspect of the invention is typically applied to cut herbs, and more preferably to woody herbs. It is known (for example, from US2002/0184897) to heat shock produce (e.g. lettuce) by immersing it into warm water (e.g. at 50°C). However, it is considered that this process leaves excessive residual water on the produce, which may accelerate the process of deterioration and/or deplete any aromatic oils present at the surface of the produce. Thus, the present invention avoids the problems inherent in known processes. Furthermore, the present invention does not require drying of the produce, and thus allows mechanical damage to the plant material to be avoided.

In the case that the herb is basil, it has been found that the most favourable results are obtained at an exposure temperature of 30-40°C. For other common herb types, such as coriander, rosemary, thyme, tarragon and mint, it is preferred that the exposure temperature is greater than 35°C, and preferably around 40°C. Preferably, the exposure time is greater than 1 minute, more preferably greater than 1.5 minutes. In general, the exposure time is less than 5 minutes, preferably less than 4 minutes, more preferably less than 3 minutes. Preferably, the temperature of the plant material prior to exposure to the humid atmosphere is less than 10°C, more preferably less than 8°C. It is thought that the temperature differential between the temperature of the plant material and the temperature of the humid atmosphere helps to promote condensation of water vapour onto the plant material. Preferably, the temperature of the plant material prior to exposure to the humid atmosphere is greater than 3°C.

Typically, the humid atmosphere is provided by passing water over an evaporator or vaporiser. In general, the water is purified (for example through reverse osmosis) and/or sterilised (for example through UV filtration) before being passed over the evaporator or vaporiser, although this may not always be necessary.

Typically, the humid atmosphere is contained within a reactor vessel (the reactor vessel is typically insulated to help maintain the temperature within the vessel). In general, conveying means are provided to convey the plant material from an entrance to an exit of the reactor vessel. In order to expose the plant material to the humid atmosphere for a sufficient time, while maintaining the size of the reaction vessel at practical and acceptable levels, and ensuring that the required processing rates are achieved, the plant material may be provided as a plurality of portions that travel through the reaction vessel in multiple parallel streams.

In this case, transfer means may be provided for transferring plant material from the exit of the reactor vessel to a further conveying means, the transfer means being configured to transfer multiple portions of plant material exiting the reaction vessel at a given time, to the further conveying means, such that the multiple portions of plant material are arranged in sequence along the direction of travel of the further conveying means.

Typically, the transfer means comprise a support plate and rotation means for rotating the support plate about an axis from a first position adjacent to the exit of the reaction vessel, to a second position adjacent to the further conveying means.

In order to avoid a reduction in the quality of the treated plant material, it is generally desirable that the plant material should be wrapped in an impervious package within two minutes (preferably 1.5 minutes) after being exposed to the humid atmosphere.

In a second aspect, the present invention may provide an apparatus for treating plant material, comprising a reactor vessel, the reactor vessel comprising:

• an inlet for allowing ingress of water;

· means for causing vaporisation of the water;

• temperature control means; and

• conveying means for conveying the plant material from an entrance to an exit of the reactor vessel,

• further conveying means for conveying the plant material away from the exit of the reactor vessel, and

• transfer means that are adapted to transfer a plurality of portions of plant material exiting the reactor vessel at a given time to the further conveying means such that the plurality of portions are placed on the further conveying means so as to provide a sequence of portions arranged in the direction of travel of the further conveying means. The transfer means may comprise a support plate and rotation means for rotating the support plate about an axis from a first position adjacent to the exit of the reactor vessel, to a second position adjacent to the further conveying means.

The invention will now be described by way of example with reference to the following Figures in which:

Figure 1 is a plan view of an apparatus for carrying out an example of a method according to the first aspect of the invention; and

Figure 2 is a section view of an apparatus for carrying out an example of a method according to the first aspect of the invention. Referring to Figures 1 and 2, an apparatus 10 for treating cut herbs comprises a weighing station 12 in which balances are located for weighing a portion of cut herbs. A conveyor belt 14 has a first section 14a that connects the weighing station 12 to a product entrance point 18 of an insulated reactor vessel 20. Second, third and fourth sections 14b, 14c, 14d of the conveyor belt are located within the reactor vessel 20, the second section 14b following an upwardly-sloping path from the entrance of the reactor vessel, the third section 14c being horizontal, and the fourth section 14d following a downwardly-sloping path to a product exit point 24 of the reactor vessel. The conveyor belt 20 has two parts 14-1 and 14-2 that travel side by side along parallel paths. A humidity generator 26 provides water vapour for the reactor vessel. The humidity cloud generated in this way typically lies above the line A-A. An exhaust outlet 28 allows vapour to be discharged from the reactor vessel, while a pulley system 32 connected to a support frame 30 allows the reactor vessel to be lifted away from the conveyor belt 14, to allow access to the conveyor belt, e.g. for cleaning.

Transfer means 34 located at the product exit point 24 of the reactor vessel comprises arms 36 extending laterally from a central axis 38. Each arm 36 supports a plate 40 that is adapted to receive herb portions from the conveyor belt 14 and to rotate about the central axis 38, to deposit the herb portions on a further conveyor belt 42 that extends away from the reactor vessel. The transfer means 34 is configured to rotate by 90° per 60s time interval.

In use, cut herbs are held in a cold store, at a temperature of around 5°C, before being transferred to the weighing station 12. The cold store may or may not be humidified. At the weighing station, the herbs are divided into portions of around 20-100g and placed onto the conveyor belt 14, which transports the herb portions into and through the reactor vessel 20. The herb portions are placed on the conveyor belt in pairs, such that each one of the pair travels on a respective part 14-1 , 14-2 of the conveyor belt.

The reactor vessel 20 is heated to a temperature of about 35-40°C (the exact temperature used generally depends on the type of herb being treated).

The rate of water entry is controlled to provide the desired temperature and humidity. The humidity is generally above 98%.

The conveyor belt 14 carries the herbs upwards into the humidity cloud. Water vapour condenses on the cold herbs, thus increasing the water content of the herbs. Additionally, the latent heat released by the condensing steam causes a "heat shock" effect, which causes oils to be released from the herbs and to become concentrated at the herb surface. The speed of the conveyor belt 14 is 2 m/min and is chosen such that the herbs remain inside the humidity cloud for about 2 minutes (the conveyor length and speed may be regulated to vary the exposure time of the herbs to the humidity cloud). After this time, the herbs travel downwards on section 14d of the conveyor belt and leave the reactor 20 via the product exit point 24. Each pair of herb portions is deposited onto a respective plate 40 of the transfer means 34, and the plate is rotated by 90° about the central axis 38, so that it moves towards the further conveyor belt 42. The herb portions are deposited onto the further conveyor belt such that they form a single column extending in the direction of travel of the further conveyor belt. The further conveyor belt transfers the herb portions to a wrapping and weighing station (not shown) at a rate of 40 portions per minute. At the wrapping and weighing station, the herbs are weighed and flow-wrapped, that is, they are wrapped in film, to provide a package having a longitudinal seal and two crimped end seals, as is known in the art. The time between the herbs leaving product exit point of the reactor vessel and the flow-wrap process being completed is less than one minute. The packaged herbs are returned to a cold store within one hour of exiting the reactor vessel.

Examples

The following worked examples are given by way of illustration only. Example 1

Coriander leaf having an initial temperature of around 5°C was held in 98% humidity at 50°C for two minutes, and the change in weight arising from the treatment was recorded. The results are shown in Table 1. Example 2

A portion of basil having an initial temperature of around 5°C was held for two minutes at 98% humidity and 50°C. The change in weight resulting from the treatment was recorded and the results are shown in Table 1. Seven days after the treatment a relative "freshness score" was determined for the portion of basil. The results are given in Table 2. Example 3

A portion of basil having an initial temperature of around 5°C was held for two minutes at 98% humidity and 40°C. The change in weight resulting from the treatment was recorded and the results are shown in Table 1. Seven days after the treatment a relative "freshness score" was determined for the portion of basil. The results are given in Table 2.

Example 4

A portion of basil having an initial temperature of around 5°C was held for two minutes at 98% humidity and 30°C. The change in weight resulting from the treatment was recorded and the results are shown in Table 1.

Seven days after the treatment a relative "freshness score" was determined for the portion of basil. The results are given in Table 2.

Example 5

Portions of rosemary and thyme (woody herbs) having an initial temperature of around 5°C were treated at 98% humidity and 40°C for 2 minutes, immediately flow-wrapped and subsequently stored for 4-5 days. The taste and aroma of the treated herbs were assessed by a panel of testers and compared to those of the untreated herbs of comparative example 5. The results are set out in Table 3. Example 6

Portions of coriander, tarragon, and mint (leafy herbs) having an initial temperature of around 5°C were treated at 98% humidity and 40°C for 2 minutes, immediately flowwrapped and subsequently stored for 4-5 days. Portions of basil were trated at 98% humidity and 35°C for 2 minutes, immediately flowwrapped and subsequently stored for 4-5 days. The taste and aroma of the treated herbs were assessed by a panel of testers and compared to those of the untreated herbs of comparative example 6. The results are set out in Table 3.

Comparative Example 1

Coriander leaf having an initial temperature of around 5°C was held in 98% humidity at 25°C for two minutes, and the change in weight arising from the treatment was recorded. The results are shown in Table 1.

Comparative Example 2

Coriander leaf having an initial temperature of around 5°C was held in 98% humidity at 5°C for two minutes, and the change in weight arising from the treatment was recorded. The results are shown in Table 1.

Comparative Example 3

A portion of basil having an initial temperature of around 5°C was held in 98% humidity at 20°C for two minutes, and the change in weight arising from the treatment was recorded. The results are shown in Table 1.

Seven days after the treatment a relative "freshness score" was determined for the portion of basil. The results are given in Table 2. Comparative Example 4

A portion of basil having an initial temperature of around 5°C was held in 98% humidity at 5°C for two minutes, and the change in weight arising from the treatment was recorded. The results are shown in Table 1.

Seven days after the treatment a relative "freshness score" was determined for the portion of basil. The results are given in Table 2.

Comparative Example 5

The taste and aroma of untreated portions of rosemary and thyme were assessed by a panel of testers and compared to those of the treated herbs of Example 5. The results are set out in Table 3.

Comparative Example 6

The taste and aroma of untreated portions of coriander, basil, tarragon and mint were assessed by a panel of testers and compared to those of the treated herbs of Example 6. The results are set out in Table 3.

Table 1

Weight gain

Example 1 (coriander / 50°C) 4%

Example 2 (basil / 50°C) 4%

Example 3 (basil / 40°C) 3.5%

Example 4 (basil / 30°C) 1 %

Comparative Example 1 (coriander / 25°C) <1 %

Comparative Example 2 (coriander / 5°C) <1 %

Comparative Example 3 (basil / 20°C) <0.5%

Comparative Example 4 (basil / 5°C) <0.5%

Coriander treated at 50°C (Example 1) exhibits higher weight gain than coriander treated at temperatures below 30°C (Comparative Examples 1 and 2).

Basil treated at temperatures between 30 and 50°C (Examples 2-4) exhibits higher weight gain than basil treated at lower temperatures (Comparative Examples 3 and 4).

Table 2

The minimum deterioration (that is, maximum retained freshness) for basil is seen after treatment at 30°C (Example 4). Table 3

Example Percentage of testing panel expressing a preference for this example

Example 5 (treated rosemary and thyme) 50%

Example 6 (treated coriander, tarragon, mint, 50%

basil)

Comparative Example 5 (untreated rosemary 30%

and thyme)

Comparative Example 6 (untreated coriander, 40%

tarragon, mint, basil)

The respondents tended to prefer treated herbs (Example 5 and 6) to untreated herbs (Comparative Example 5 and 6). The difference was more marked for woody herbs

(Example 5 and Comparative Example 5) than for leafy herbs (Example 6 and Comparative Example 6).