How important is the temperature of cakes at the point of wrapping

Cakes can be wrapped at either high temperatures or completely cooled. In either case the important point is to ensure that no localised condensation occurs on the surface of the product which might result in mould growth during storage. The equilibrium relative humidity of the product should remain at the level required to achieve the desired mould-free shelf-life (see 10.9).

If a cake requires no filling, coating or other finishing after baking there is no reason why it should not be wrapped direct from the oven at a temperature of about 88-93 °C (190-200 °F). Obviously there may be some difficulties involved in wrapping at these high temperatures, such as damage to a fragile product and control of condensation as the product cools. Provided the wrapping material is in reasonably close contact with the product, condensation soon disappears even when a moisture-impermeable film is used.

Materials for wrapping at high temperatures should be chosen with care. Materials such as polythene would be unsuitable, but most grades of cellulose film do not appear adversely affected by hot wrapping.

If products are to be cooled and then wrapped care must be taken during the cooling process. Rapid cooling can be achieved with suitably high air velocities. However, if drying out of the product is to be prevented, the relative humidity in the cooler must be carefully controlled. The relative humidity can be controlled only if the air temperature is closely regulated since relative humidity changes rapidly with a small change in air temperature at a given moisture vapour content.

If refrigeration is used both temperature and relative humidity can be controlled satisfactorily with an air temperature of, say, 16 °C (60 °F) and about 80-85% relative humidity. To prevent the product drying out the relative humidity should be close to the equilibrium humidity of the product (typically 80-85% for cakes) so that moisture is not encouraged to move from the product. The high relative humidity in a refrigerated system means that large cooling plates are required to prevent condensation of moisture onto the cooling coils.

Without refrigeration, relative humidity can be controlled using water spray type humidifiers. In this case close control is more difficult especially if the air temperature (around 21 °C, 70 °F) is subject to fluctuations.

The moisture loss from flour confectionery products during cooling may be a critical factor in determining their mould-free shelf-life and eating qualities. If controlled cooling conditions are used it is possible that an increase in the moisture content of the product could occur with a resulting reduction in the shelf-life. It is advisable to make careful checks on moisture content when setting up the cooling system and recipes may need adjustment to decrease the ERH of the product.

Under controlled cooling conditions, it is important that any air blown over the product is clean and thorough filtering of air drawn from outside is desirable. Cooling times are dependent on the size and thermal conductivity of the product.

It is pointless using high air velocities with large products, where cooling time is controlled mainly by the time taken for heat to be conducted from the centre of the product to the outside. See also 10.6, 10.8 and 10.9.

Further reading

CAUVAIN, S.P. and YOUNG, L.S. (2000) Bakery Food Manufacture and Quality: Water control and effects, Blackwell Science Ltd, Oxford, UK.

Continue reading here: What precautions should we take when freezing flour confectionery products

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