The Wafer Oven or Wafer Baker

The oven is the heart of the process as it both forms and bakes the wafer. It consists of pairs of strong plates that are either self supporting or fixed to heavy carriers linked together to form a chain. The chain of plates is circulated continuously through an insulated box (oven) where the plates are heated either by direct impingement of gas flames or individually by electric heaters arranged in the backs of each plate. The heavy carriers are required not only to support the plates and to keep them rigid, but also to maintain their parallel positions against the steam pressures as the baking proceeds.

The sheets produced are typically 470 x 290 mm (of between 50-56g in weight). Mid sized plates are occasionally used, these are 370 x 240 mm and 470 x 350 mm but there is a growing use of "Jumbo" plates of 750 x 350 mm (producing sheets of about 90g). Plates producing sheets larger than the "Jumbo" ones will give difficulties in removing moisture from the centres of the wafers.

At one end of the oven the plates open to allow release of the cooked sheet and then, almost immediately, to receive a spread of batter for another wafer. As engineering techniques have developed the length of oven chains and number of plate pairs has steadily increased so that presently up to 120 plate pairs may form a single plant. The most common oven size are between 72-96 plate pairs, however, on older installations 60, 45 and 30 plate pairs are commonly found. Older ovens have the plates mounted to run length ways (the shorter edge leading) through the oven whilst now plates are almost always mounted transversely with the longer edge leading. This has the effect of reducing the oven chain length and therefore reducing the speed that the chain must move for a given baking time.

The plate surfaces carry designs that may be artistic or ornate or simply reticulate patterns of V grooves of various depths. To give the wafer sheet maximum strength the grooves in the upper plate are usually at 45° to those in the lower plate. The depth of the grooving, or reeding as it called, ranges from 0.3-0.8mm with 0.5 - 0.8mm being the most common. The depth of the reeding must be related to both the overall thickness of the wafer (determined by the gap set between the plates) and the end use of the wafer. For example, for wafers that are to be chocolate enrobed, it is preferable to have shallow reeding as the surface will retain less chocolate.

3cl-Examples-of-wafer-re-thExamples of wafer reeding patterns

Wafers may have deep reeding but this is usually on one side with shallower reeding on the other. When sandwiched with cream, jam or caramel only two wafers are put together as the amount of filling needed to fill the deep reeded side would be excessive.

3cl-examples-of-deep-thumbExamples of deep reeding patterns

Hollow wafers are baked with plates which have deep cavities and the corresponding plate that marries has protrusions. The wafer sheets therefore when placed back to back form hollow balls which can be filled with cream and then punched out from the sheet pairs.

The surface of the plates may be simply cut into the steel with a micro-machined finish or may be chromium plated for a smoother surface and better release of the baked wafers.

In order that the wafers may be full rectangles and of even thickness overall, the plates are edged with strips which overlap the other plate when the pair is closed. Steam must be allowed to escape at the edges so indentations or vents are cut in the surfaces of these strips, and the size and number of these vents is critical to the quality of the wafers produced. Batter is deposited, usually in lines, across the lower plate, and on closing and locking with the upper plate the very rapid production of steam not only spreads the batter evenly throughout the gap between the plates, but also to a certain extent out through the vents. A minimum extrusion through all the vents is the aim because that which emerges, and is subsequently baked in the passage through the oven, represents waste product that, incidentally, is more or less valueless even as animal feed. The extruded matter is known by various names such as "bubble", "bobble", "dross" or "doddings". The waste of ingredients as a result of bobble formation can be between 4 and 8% (but as the moisture content of the bobble is about 30% moisture, the weight of what is collected will seem to be more) on a well adjusted oven. Clearly, if the oven is not in excellent adjustment and batter is applied to ensure that all the sheets are full, the bobble may be as high as 15%.

The thickness of the wafers is proportional to the gap between the two plates.

The quality of wafer sheets is judged principally by their weight, surface colour and uniformity of moisture content. Texture and crispness tend to be related to one or more of these properties, but basic differences in wafer sheet thickness will affect the internal structure. Differences in recipe have little effect on the flavour but they will affect the spreadability of the batter and the colouration of the sheet during baking.

The prolonged successful operation of a wafer plant is very largely due to engineering developments and in particular to the lubrication of bearings which, by necessity, become very hot due to the proximity to the heated plates.