VHT Vapour Heat Treatment
Vapor Heat Treatment is a Plant Quarantine treatment method used around the world anywhere phytosanitary is required for exporting of fresh fruit to Japan, South Korea, China, Australia, New Zealand, EU and elsewhere. The Vapor Heat Treatment System (hereafter “VHT System”) is a system for steadily killing eggs and larvae of fruit flies parasitizing inside the fruit with vapor and heat without injuring fresh fruits. The system operates on the following basic principle: The fruit is exposed to heat at specified temperature and humidity levels, increasing its internal temperature. As a result, parasites are killed while heat injury to the fresh fruit is avoided. The system of equipment is called the “differential pressure treatment system.” Treatment systems of this type use differential pressure to induce efficient circulation of vapor heat through all spaces in-between fruits so that each and every individual fruit is continuously, evenly and uniformly exposed to vapor heat atmosphere. Currently, almost all fresh fruits being imported to Japan on the condition of VHT are processed with a differential pressure type treatment system.
For insecticidal sterilization using heat, there are dry-heat-treatment, vapor- heat treatment, hot- water- dipping. Dry-heat-treatment is the most common and is easy to use it, but transpiration of the water is generated from the fruit surface by drying. As a result, the fruit withers away, and article value is lost. When Dry-heat-treatment looks from the viewpoint of thermal efficiency, heat gradually reaches the inside from the fruit surface by conduction, but evaporation heat is robbed of it to have transpiration of the water at the surface of the fruit, and this acts on a minus for a rise of the temperature. Hot- water- dipping does not produce the loss of the heat called the evaporation heat, but control is difficult, and there is a problem that the influence that even the same temperature gives fruit again is intense in comparison with the air. Vapor- heat-treatment is processing with the saturated vapor, and this high humidity prevents water transpiration from fruit, and heat loss called the outbreak of the evaporation heat does not occur. In addition, the air of the high temperature high humidity and an encounter with the temperature of low fruit cause dew condensation on the surface of the fruit. This dew condensation phenomenon has two meanings. As for one, heat of condensation (latent heat of the vapor) to occur when air turns into a liquid works in a plus for a craze for conduction, and dew condensation to produce on the fruit surface other let’s surface area to receive heat increase and makes conduction efficiency of the heat better.
When a drop of water of 1ml reached the fruit surface of 100g, the effect of the heat of condensation calculates, and it is thought that this is equivalent to heat capacity to nominate temperature of the fruit for more than 4 degrees Celsius. Therefore, it is said that the thermal efficiency of vapor heat is far superior to dry heat.
【Fig .1】 Heat conduction in case of Dry heat treatment
【Fig.2】 Heat conduction in case of Vapor heat treatment
COUNTRIES WHERE IT IS MANDATORY/ACCEPTED
China, Taiwan, Vietnam, Cambodia, Thailand, Philippines, Malaysia, Indonesia, India, Sri Lanka, Pakistan, Australia, USA(Hawaii), Peru, Colombia
