Biomedical Engineering Reference
In-Depth Information
Applying quality control plans and good manufacturing practice to eliminate hazards
and possible contamination can be integrated easily in cook-chill/cook-freeze
production systems.
7.6.2.2
Heating Techniques
The most common systems used for cooking/heating are water bath or steam. However,
conventional heating systems can produce an inconsistent heating profi le, especially if
large volumes of food are processed. Sheard and Rodger (
1995
) examined ten heating
systems and reported that none of the convective steam ovens heated sous-vide pouches
uniformly under fully loaded operational conditions. It took 16-85.5 min to increase
the temperature of sous-vide pouches from 25 to 75 °C. The variations depend on the
location of the product within the oven as well as the types of oven. The circulating
water baths provided uniform heating with a variation of 0.05 °C. It is important to
submerge the pouches (in a rack) during cooking to avoid undercooking or potential
microbial growth during post-processing (Rybka-Rodgers
1999
).
7.6.2.3
Rapid Chilling or Freezing Equipment
The refrigeration systems used for REFPFED are: blast chillers, blast freezers or
combination of both. These are capable of rapid reduction of temperature of hot
foods (+70 °C) to low safe storage temperatures (+3 °C or −18 °C). The basic prin-
ciple of food safety in cook-chill food products is the start of cooling as soon as
cooking is fi nished and the fi nal core temperature of the product should be below
4 °C. This can be achieved using specially designed rapid chillers, such as air-blast
chillers and vacuum coolers. These are capable of decreasing the temperature of the
hot food to 0 °C or +3 °C within 90 min. This ensures the product safety as well as
preserving the sensory attributes. As the fi nal cooling temperature and the rate of
cooling are crucial control points in this process, chillers are normally equipped
with temperature probes at various locations to monitor the process.
There are two main methods of cooling used for cook-chill and sous-vide prod-
ucts: blast chilling and water bath chilling. In blast chilling, cold air circulates over
food containers (usually shallow pans), while in the water bath method, cooked
food containers are submersed in cold water. Rapid cooling or freezing (also known
as hard blast chilling) is used for dense, large products with high fat content (e.g.
meat based sauces, meat joints, mashed potato and lasagna). The air temperature of
the cabinet, normally below the freezing temperature of the product, must ensure
that the core of the product reaches the required +3 °C within the 90 min. A slower
chilling rate is obtained by “soft blast chilling”. This technique uses air temperature
above 0 °C in order to avoid any damage to delicate and light products, such as fi sh,
rice, vegetables, cream, desserts, cakes and fried foods. Therefore, the soft blast
chilling cycle smoothly lowers the product core temperature to +3 °C over 90 min
without compromising the quality of delicate products.
