Heat Treatment of Mills. How effective is it?

12 June 20176 min reading

“Heat treatment is a realistic and effective method for killing insects in mills. However is not applied in many countries around the world as a significant investment in equipment is needed. Where available Heat Treatment shall be the miller’s first choice.”

Vasilis Sotiroudas Food Scientist Control Union Greece

controlunion90We are on the ages of Precision Fumigation. The old style treatments of “run n gun” or “shoot n pray” shall be totally eliminated. They were never useful anyway. They brought us insect resistance and life threats.

In the 70s the fumigators were wizards with the secret knowledge! In the 90s the fumigators were scientists who respected protocols and paid attention to details. Today a fumigator shall be a tech-gig! Technology is our new major weapon. We can have eyes inside chambers and silos. We can have real time info on our Smartphone. We can predict and respond with the touch of a button. There are no more excuses for failures. And heat treatment is the new trend.

THE HEAT TREATMENT PRINCIPLES Several researchers have tested insect behavior at elevated temperatures. They all agree that 50C will kill all insect stages in a few hours. Insects die because the proteins in their bodies coagulate, the salt balance is interrupted, their enzymes are destroyed and they dry out. The young larvae of Tribolium was found to be the most heat-tolerant species and stage, so it has been used in research as the insect of reference.

This insect will die in 7 hours at 50C, or in less than 10 minutes at 60C. With my team we have been working over 10 years with heat treatment and our protocol requires maintaining the temperature between 55-65C for 10 hours. We need 10-20 hours to reach this level, so the whole heat treatment duration is 20-30 hours.

DAMAGES? We have a letter from Buhler who states that their machinery can take 60C without any problem. In all these years of experience we have heat treated mills of several other manufacturers apart of Buhler and they all showed the same response: no damages.

To avoid any trouble do the following: • Check the glue used in the plan-shifters. It should stand 70C. • Remove pressurized bottles from the mill during heat treatment. • Avoid pointing the heaters directly towards machinery. • Loose belts. • Always select an experienced team with a good monitoring system.

HOW DO WE RAISE THE TEMPERATURE? The best heaters we have used are electrical or gas. Petrol and steam heaters did not perform so well in our hands. The brands we trust are ThermoNox, Temp-Air and We must always have more than enough heat-capacity for the volume to be treated. Calculating the capacity needed is not easy as the type of building plays an important role, as well as the weather conditions. For example, a building of 10,000m3 of volume may require 15 electrical heaters (380V, 640 Amps) if it is made of panel and has a tall roof. Or the same volume may require 30 electrical heaters if it is made of concrete, with a basement and 3 floors.

EMPTY SILOS – FULL SILOS Empty silos can be heat treated. They need specific type of heaters especially if they are made of concrete. Full silos cannot be heat treated. If they remain full (with grain or flour) during a heat treatment they may become a harborage for insects that will survive the treatment. The heat will not affect the product but the insects will survive. It is important to make a mill completely empty for a heat treatment. A final product warehouse is usually not heat treated, but should be sprayed of fogged.

MONITORING A monitoring solution must include wireless durable sensors and clever software. The real time monitoring limits the number of humans entering the building under treatment. The best available monitoring solution that we have used is provided by Centaur Analytics. It includes color-coding, alarms and kill-rates based on research made by 3 different Universities.

Important points A heat treatment must always be followed with an extensive spraying of the outside walls and roof of the heat treated buildings. Insects may find a way out of the building through tiny holes and survive the heat. They will return when the treatment is over. Through spraying with contact insecticides, we erase the possibility of survival.

Failures Failing a fumigation means letting a number of insects to survive. Even a small number of insects (like 10%) is very bad news. To get an idea of how fast the rebound effect will be (insects getting back to the same population like before the treatment) we shall look into the stored product insects’ biology: As a rule of thumb, insects under favor conditions multiply to the square (10 insects in 30 days will become 102= 100 insects). This means that letting 10% of insects to survive after a fumigation, you get a very fast rebound effect: Initial population of insects= 100. We kill 90% of insects , so 10 insects survive. Under favor conditions, 10 insects will become 102= 100 insects in 1 month. So we are back to the initial population.

A failure at heat treatment can happen if we do not have enough heating capacity and we leave some cold spots or if we do not have good monitoring and leave cold spots. Both reasons are avoided when an experienced team is selected.

ALTERNATIVE METHODS Fumigants may be used in a mill but all popular fumigants have their own disadvantages. • They all need gas tight buildings. Such buildings are not so easily found around the Mediterranean countries and in places where the weather is warm. A lot of resources and attention shall be paid on making a building gas-tight for a fumigation. • Monitoring of a fumigation requires resources, planning and experience. • Methyl Bromide is not available in most countries as it depletes ozone. • Profume is not registered in many countries. It requires temperatures higher than 26C to kill the eggs and attention shall be paid to dosages to avoid residues. • Phosphine reacts with copper and may damage electronics. Additionally we must check for insect resistance before selecting the dosage and time. Phosphine will require at least 5 days of treatment plus aeration.

Heat treatment is a realistic and effective method for killing insects in mills. However is not applied in many countries around the world as a significant investment in equipment is needed. Where available Heat Treatment shall be the miller’s first choice.

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