Double Draper Water Blanchers
VOL. 19 NO. 10
Double draper water blanchers will process just about any product that can be water blanched. Because of considerably higher cost than other types of water blanchers, they are normally used only on products that are either fragile or difficult to control. A modern double draper water blancher has a bottom draper consisting of a wire mesh belt with moving side plates, flights and side chains. The mesh belt, side plates and flights form a series of open top boxes traveling through the blancher. The top draper, consisting of wire mesh belt with side chains, forms a lid for the boxes. This results in a series of closed compartments, assuring positive control of product traveling through the blancher.
This belt design, first used for broccoli, was developed to address problems with an earlier configuration utilizing two inch pitch chain and two inch sheet metal panels with short full width flights. The sides of the blancher tank doubled as the sides of the product chamber and the flights only reached part of the way to the top draper, which also used the two inch chain and panels. Broccoli drifted back and forth through the space between the flights and top draper, resulting in simultaneous production of both under-blanched and over-blanched product.
Heat is normally provided by direct injected steam. For most products steam pipes, located below the bottom draper, direct steam down at a forty-five degree angle toward the bottom of blancher tank. This provides opportunity for the steam to mix with the water. The hot water gently circulates through the bottom draper to heat the product. For fragile products, like broccoli, the objective is to heat the water and provide only a mild amount of turbulence. Too much turbulence can result in product damage. At the other extreme, leafy products, like spinach, require a substantial amount of turbulence to achieve a satisfactory blanch. This was learned the hard way with the first double draper spinach blancher, practically an exact duplicate of units manufactured for broccoli. Spinach formed a mat in the blancher. At the discharge, the outside of the mat was well cooked and the inside was still raw. Fortunately the customer was very sharp. He addressed the problem by installing steam pipes above the top draper and below the bottom draper with the holes pointed toward the product area. The jets of steam formed enough turbulence to break up the mat, resulting in evenly blanched product.
Double draper water blancher design is flexible. For large particle size product, such as cob corn, clearance will be provided between the top of the flights and the top draper to avoid damage caused by jamming product between flights and the top draper. Blancher tanks can have either manually removed lids or a power actuated lift top. The power actuated lift top can raise the belts to provide sanitation and maintenance access. To provide even better accessibility, provision can be made to lift the top draper clear of the bottom draper when the lid is fully open. For difficult water blanching applications, the double draper design is often worth the extra cost.