IELTSDATA READING PASSAGE 78-TOMATO RIPENING.
Tomatoes give off minute quantities of ethylene gas which is active in starting the natural ripening process. If left to nature; however, the tomatoes ripen in a random way. The trickled ethylene gas process of tomato ripening consists of exposing the tomatoes to a low concentration of ethylene gas under controlled temperature conditions in a special tomato-ripening room. This treatment initiates and controls the speed of the natural ripening and coloring process in the tomatoes.
Controlled ripening and coloring enable the grower to market tomatoes of more uniform color and quality than is possible with green or field-ripened produce. The timing of harvesting and marketing may, within limits, also be regulated by the use of controlled ripening and coloring in order to achieve maximum returns and make the best use of labor and equipment.
All fruit must be mature green at harvest for controlled ripening to be successfully carried out. Relative humidity does not appear to be of great importance in the tomato-ripening process. Little moisture loss from the tomatoes occurs during the ripening process due to the relatively impermeable nature of the tomato skin. Ripening time will depend on the ripening temperature range, however, ripening temperatures above 24°C will result in poor color development with yellow or orange fruit rather than red. The heating and cooling capacity should be such that the tomatoes can be brought to the recommended ripening temperature within 24 hours.
A typical arrangement for a tomato ripening room is shown in Figure 1 with the essential components of the system identified.
Room Size and Construction
For efficiency and convenience in operation, on-farm tomato ripening rooms are usually sized to accommodate the normal daily tomato pick during the peak harvest time. The room capacity is generally in the range of two to ten tonnes of tomatoes; however, larger rooms may sometimes be installed. Since the average ripening time is three or four days, the provision of multiple rooms on the one farm is generally desirable.
Air Circulation and Ventilation System
Fan-forced air circulation is required for adequate and uniform temperature control and ethylene gas distribution in the ripening room. An air circulation rate of two room air volumes per minute is recommended for good results. This is equivalent to around 480 cubic meters of air per hour per tonne of tomatoes. At the recommended heating or cooling capacity of 0.6 to 1.2 kW per tonne of tomatoes, this gives an air temperature differential of 3.5 to 7°C across the heating or cooling system. These high air circulation rates are necessary to limit variations in temperature in different parts of the room to acceptable levels and to achieve an adequate rate of heating or cooling of the tomatoes. The ventilation system circulates the room air continuously, introducing a small proportion of fresh air and exhausting a similar amount of air at the same time. This prevents a build-up of ethylene gas in the room and also removes carbon dioxide produced by the fruit during respiration. If this carbon dioxide were allowed to build up to too high a level in the room atmosphere, it would interfere with the ripening process.
Temperature Control System
The temperature of tomatoes in the ripening room has a great influence on the ripening process. In fact, the product heat load usually represents around 80% of the total heat load. The remainder is due to heat transmission through the external walls of the room and the fresh air exchange rate. In some cases, both heating and cooling are required to maintain the room temperature within the required range. The time required for ripening can be reduced to some extent by increasing the temperature. Reverse cycle air-conditioners are successfully used for both heating and cooling in tomato-ripening rooms where humidity control does not appear to be of great importance.
Supply and Control Systems
With the trickled ethylene gas system, a low concentration of ethylene gas is maintained in the ripening room atmosphere by a continuous small, controlled flow of gas of about 10 parts per million (ppm). Ethylene gas is supplied as a bottled gas under high pressure and it is released into the ripening room through a pressure regulator and metering system. The outlet gas pressure is adjusted by means of the gas pressure regulator and the gas flow rate is then adjusted by the fine needle valve. A normally closed solenoid valve in the ethylene gas supply line ensures that gas is not discharged into the room unless the fans and ventilation system in the ripening room is operating. The solenoid valve is electrically interlocked with the operation of the ventilation system fans and is also controlled by an air flow switch. A gas control thermostat is used to measure when gas should be supplied to the room. The temperature-sensing element of this thermostat is pushed into a tomato so that it senses the pulp temperature of the tomatoes in different parts of the room. Provided that the ethylene gas supply and control systems are correctly arranged, the ethylene gas concentration in the room will not exceed the low level which is sufficient for ripening but is far below the explosion hazard level. Under these conditions, tomato-ripening rooms installed on farms and used only for ripening fruit produced by the owner have been approved by certain Electricity Commissions as not constituting a hazardous location.
(Adapted from an article written by Brian Hesse for the ‘Electrofarming Notebook’ for The South East Queensland Electricity Board, October 1989.)
Questions 1– 3:
Complete the table in the box below. Use NO MORE THAN THREE WORDS OR A NUMBER for each answer.
Requirements for successful use of the Ethylene Gas System for Tomato Ripening:
14. Tomatoes should be picked when they are _____________.
15. Room temperature must be ______________ °C.
16. Optimal ripening temperature for fruit must be achieved ___________.
Questions 4– 7:
Complete the flowchart below using information from the text. Use NO MORE THAN THREE WORDS for each answer. Write your answers in boxes 4– 7on your Answer Sheet.
Questions 8— 14:
Below is a list of assumptions. Using the information given in the passage, choose:
TRUE if it is a reasonable assumption
FALSE if it is NOT a reasonable assumption
NOT GIVEN if it is not possible to make the assumption from the information in the text.
Write your answers in boxes 8– 14on your Answer Sheet.
Example: Ethylene gas systems improve the grower’s chance of selling the tomatoes.
8. Carbon dioxide is not beneficial to the ripening process.
9. The outside air temperature determines the amount of extra heating needed in the ripening room.
10. Increased temperature can speed up the maturing process.
11. For successful tomato ripening, humidity levels need to be carefully monitored.
12. The solenoid valve has to be checked at regular intervals.
13. A build-up of ethylene gas may result in an explosion.
14. Setting up ethylene gas ripening rooms is not always safe.
1 . (MATURE) GREEN DEVELOPMENTS
2 . UNDER / BELOW / UP TO / LESS THAN 24
3 . WITHIN 24 HOURS
4 . Color / COLOURING (PROCESS)
5 . VARIATION
6 . CARBON DIOXIDE / ETHYLENE GAS
7 . ETHYLENE GAS / CARBON DIOXIDE
8 . FALSE
9 . FALSE
10 . TRUE
11 . FALSE
12 . NOT GIVEN
13 . TRUE
14 . TRUE
IELTSDATA READING PASSAGE 78-TOMATO RIPENING IELTSDATA READING PASSAGE 78-TOMATO RIPENING IELTSDATA READING PASSAGE 78-TOMATO RIPENING IELTSDATA READING PASSAGE 78-TOMATO RIPENING IELTSDATA READING PASSAGE 78-TOMATO RIPENING