Convection vs. Conduction

1. Sanitation & Hygiene
Convection systems allow for detailed cleaning of the interior and exterior of the retherm system. The interior of a convection retherm system is a fully open cavity. This allows the foodservice staff to power wash the interior and exterior of the units. The rack system inside the unit is removable which allows for hand washing of the complete system. There are no pod heating elements that have to be removed by the technical services department before the cleaning process can begin (as in conduction systems). In a conduction system, if food over heats or boils over, food will build up behind the food pods. Foodservice staff will not be able to properly clean behind the pods thus creating a greater sanitation, hygiene, and compliance risk issue with the foodservice departments HACCP (Hazard Analysis Critical Control Points) policy’s.

New conduction systems demand less removal requirements of the pod heating systems. However, due to the electronics of the system ( wires from the main panel to the heating pod ), it is recommended that the pods be removed by maintenance technical personnel only. This is to guarantee the safety of the individuals that are properly sanitizing the conduction system.

2. Quality of Food
I encourage you to call people who use conduction or used to use conduction systems. Ask them what happened to their customer satisfaction scores after they implemented Convection in place of the old conduction system they had prior. You will hear some remarkable results. The entire convection system supports quality – in everything it does – it reheats all types of foods (breaded, fish, fries, baked desserts, toast), it does not result in baked on food onto the dishware, it allows for all types of dishware, most convection systems use a FLAT TRAY which is homelike and allows for all foods to be easily moved about on the tray without obtrusive ridges or holes.

3. Multiple Handling of Foods?
In convection systems, the food is placed cold onto a tray and placed into a retherm cart where the food is reheated while the cold food stays cold. When the retherm cycle ends, the food tray is pulled out and given to the patient. That is the process. In conduction systems, food is placed on the tray in specific locations as each system has ‘spots’ to have foods placed on the tray. The food must be specially plated due to the conduction heating process. The tray is moved to the conduction ovens. In some cases, the trays can be inserted into the oven which will keep the foods cold that are to be cold while the hot foods reheat…however, some systems require you to transfer the foods from one hot retherm cart to the tray that is being held cold. This is done with the use of a ‘shovel’. This is true food manipulation, which is not the case with convection single handling flat tray systems.

4. Noise
A common argument against convection retherm systems is that the noise level emitted during rethermalization is substantial when compared to conduction based systems. It is true that convection based systems are noisier than conduction systems because of the fan inside the convection unit. However, the convection unit is well insulated and the noise emission is well within the limits. The noise of a group of retherm units is no louder than that emitted by one single fan inside a walk-in fridge.

5. Heat Distribution
Conduction systems use a pod and heating element system. The stainless steel or aluminum plate has a heating element inside. The element is energized from the incoming power supply, for which the heating element then heats the pod. The pod then heats the bottom of the entrée plate or soup bowl, which then heats the food from the bottom to the top.
Convection systems use a heating element and a fan system to gently distribute hot air through-out the entire cavity. This allows for the heating of the complete surface area of all items that are required to be rethermed.. This even distribution allows for maximum efficiency and guarantees all foods are heated. There are no ‘hot spots’ and trays are not discolored at contact points. Today’s healthcare production facilities require convection based cooking and chill equipment in order to provide maximum food quality, taste and appearance. If food is cooked using convection based heat, then it is prudent to rethermalize it using the same process.

6. Maintenance
Conduction systems over a ten year period require greater maintenance attention and costs than convection systems. General replacement parts on the conduction equipment on average are the heating pod systems. Estimated replacement value is approximately $ 250.00 per pod.
Convection retherm systems require an estimated twenty minutes of cost time per year for preventative maintenance measures. During the following years preventative maintenance is estimated at 30 minutes per retherm unit. General components that may need to be replaced should the system fail are: fuses, consumable items, and or warranty components, such as the main contactor or run capacitors. In the long run, convection systems are easier and low cost to maintain. You really need to consider life cycle costs when evaluating convection versus conduction.

7. Worker Safety & Food Product Safety
When rethermalization is completed on a conduction system a foodservice staff member must check each heated item on every tray with a sanitized food probe to ensure that each item has reached the required safe set temperature. There is a labour and time management cost associated with this process. Staff must and are required to sanitize their product probe prior to probing each food item. This is a mandatory requirement to ensure that a product previously probed for one patient does to not come in contact with other food items for another patient that may have allergies. To avoid this process, many foodservices have adopted a specific process with conduction systems. Staff place there hands on the under-section of the heating pod to test to make sure that the heating pods are operating as required. Staff can complete this procedure without the use of protective gloves. They do this to ensure that they can accurately test the pods, and that the pods were working through the complete retherm process. This procedure can result in burns and bending injuries, which in turn, can result in lost time and a workers safety insurance claim. Claims can be estimated to cost the foodservices department as much as two and half times the individual claimants salary to the hospital.
In addition the aforementioned, you should review the ergonomics of a cart system before you make a choice. You may find that the conduction systems are extremely heavy compared to convection systems. And, if you find the reverse, then we encourage you to review the fabrication of the conduction cart as many manufacturers decrease the durability of a cart to loose weight.

8. Equipment Failure?
Some suggest that when a convection system ‘goes down or out of service’ the entire set of trays are at risk of not getting heated. There is no argument to this. The same can be said for a conduction system as all the trays would be compromised as well if the cart went down. The real issue is that when something goes wrong in a conduction system how are you assured you know ? One pod may not work and how do you know that it has ‘gone down’. You only truly find out after the retherm cycle is finished and you find a cold food tray. In a convection system, if the entire cart goes down, you will know it and corrective action can be taken immediately. If the cart goes down for any reason, another cart can be used. For what it is worth, cart failure that impacts meal service to a point of complete failure to supply a meal is extremely rare. In a convection system for example, there is one fan and one heating coil….not 20 pods and 20 wires.

9. Dishware
Speciality china should be utilized when operating a conduction system. Flat based bottom china provides a better transfer of the heat from the heating pod to the bottom of the entrée plate or soup/cereal bowl. In some systems, heat may be transferred from the heating pod to the patient tray and from the patient tray to the bottom of the individual china pieces. Single tray conduction retherm systems have experienced major problems with tray warping and the break down of the plastic material used in the composition of the tray. Trays become discolored and unattractive. Replacement costs are high and ongoing. In some cases, operators using conduction systems have noted patient complaints about odors coming from trays and in one case the odor caused a patient to become extremely ill. The plastic odor being expelled from the trays was being absorbed by the patient’s food, the odor was the main contributing factor to the patient illness.

In conduction systems, special china must also be used. Flat-bottomed china is required so that heat transfer can take place effectively. Flat china is often heavier than other china and thus the weight of the cart can become an ergonomic issue to the occupational health and safety department.

Conduction systems often have ridges on the trays, thus a flat tray is not possible. The tray (in many cases) must be inserted into the retherm cart the same exact way each time. There is no opportunity to reverse the tray, thus one side will always be exposed to heat. This will discolor the tray over time and will shorten the usefulness of the tray (i.e. life expectancy).

Convection allows the foodservice department the ability to use china, high heat plastic, oven paper and foil based products from a wide variety of manufactures. Foodservices can also add a tray mat to increase the appearance of a patient tray to allow for a home style appearance. Many convection systems have a tray that does not have to fit a special way and thus the life expectancy of the tray is much longer.

10. Menu
Menu styles and needs of the hospital’s patients are as flexible as requirements of the production department’s recipes. Production equipment for the cook chill kitchen is based on the operation of convection ovens, convection combination ovens and convection air Blast Chillers. The standardized method of operation has been adopted by all cook chill facilities on or before 1947. Kitchens continue to be designed based on this principal. It allows the foodservice departments the ability to produce and store a wide variety of menu items based on the principal of completing the cook chill chain by utilizing convection air retherm technology.

When conduction technology is adopted as the principal rethermalization, special production procedures need to be adopted. Conduction systems generally place a certain amount of condensation back into the items to be rethermed. Therefore, produced items need to be dryer in content to compensate for the weeping that will occur in a conduction system. Special plating techniques must also be adopted with conduction technology. Meats will require gravy underneath them to retard the heating process. If this procedure is not adopted meat gives the appearance and taste of a dried out product. Boned items cannot be used (such as chicken or pork) or care must taken not to allow the bone to touch the plate. If the bone touches the plate, the heat is transferred into pours of the bone and is not transferred to meat of the chicken. Conduction systems cannot rethermalize crispy items such as Chicken Fingers, Toast, French Fries, melting cheese on a lasagne. Convection systems can retherm all food groups and even bake off cookies and other desserts do the patient receives a fully cooked and warm dessert.

In convection based systems, all forms of foods can be used and no special plating instructions are truly required to make sure the food is reheated.