This document discusses methods for chilling and preserving fresh fish, including chilling, superchilling, and freezing. Chilling involves cooling fish to near-freezing temperatures using ice to extend shelf-life up to 30 days for some fish. Superchilling involves lowering temperatures slightly below the freezing point of fish between -0.5 to -2.4°C to further preserve quality and reduce spoilage compared to conventional chilling. The document describes the original Portuguese method for superchilling aboard fishing vessels using refrigerated brine circulated through metal shelves and packaging to achieve superchilling temperatures throughout the catch.

1. CHILLINGOFFRESHFISH
G BHARATHI
Assistant Professor
Department of Food Technology

3. INTRODUCTION:
◦ Fish is a highly demanded and nutritious food product, yet perishability remains the
biggest challenge for its preservation . This food must be stored refrigerated or frozen,
and, even under those conditions, it has a very short shelf-life, particularly for
refrigeration (5–7 days and 9–12 months under refrigeration and frozen conditions,
respectively). The deterioration of fresh fish during storage is attributed to different
damage mechanisms, like microbiological spoilage, autolytic degradation, and lipid
oxidation

4. METHODS OF CHILLING:
◦ The preservation of food products without using preservatives or additives has been
increasingly demanded among consumers, and has brought additional challenges,
especially to highly perishable foods, such as meat or fish.
◦ Low temperatures during the capture, transportation, and storage of the fish are of major
importance worldwide. Chilling, superchilling, and freezing techniques allow for the
preservation of fish for longer periods without major changes in quality, and assure
economic benefits for the fish companies.
◦ Therefore, chilling is one of the most used methods for fish preservation, along with
freezing and, recently, superchilling.

5. CHILLING:
◦ Chilling is the process of cooling fish or fish products to a temperature
approaching that of melting ice, using, for example, ice. Chilling promotes an
increase of shelf-life by slowing physical and chemical reactions and the action
of deteriorative microorganisms and enzymes.
◦ Usually done with ice, chilling can maintain the fish at temperatures close
to 0 °C and extend the shelf-life up to 30 days (in fatty fish, this can be up
to 40 days), depending on several factors, such as the water temperature
(temperate or tropical waters) and the type of species (marine or
freshwater species)

7. Changes in fish during the chilling/icing process:
◦ i. Protein and weight loss: The fish chilled with ice shows gradual weight loss in the lower layers.
Losses which occur in iced fish fillets and steaks are largely or entirely due to formation of free liquid
drip. Melting water carries with it a considerable percentage of soluble proteins, salts, other
flavouring and nutritive substances of the fish.
◦ ii. Discolouration: Excessive pressure of ice on fish during chilling results bruising and damage
and consequent discolouration of flesh during icing. If the fish is not gutted soon after being caught,
the powerful digestive enzymes attack the viscera and belly walls called belly burn or disruption
in course of few days at ice temperature which also cause discolouration. It is well known that
pelagic fishes with full of stomach may develop torn bellies long before the sign of spoilage set in.
◦ iii. Rancidity: In case of fatty fishes in low temperature at even 0 to –2oC, rancidity may develop and
the rancid flavour becomes a limiting factor of keeping quality during long time storage in ice.
◦ iv. Shrinkage: Shrinkage is a common phenomenon in fish packed with ice, particularly in the
upper layers. The shrinkage in the lean fish is higher than that of fatty fishes. Subcutaneous layer of
fat serves to reduce the evaporation of tissue moisture

8. SUPER CHILLING:
◦ Super chilling, also known as partial freezing or deep chilling, is
characterized by low temperatures (between conventional chilling
and freezing), in which a decrease of 1–2 °C occurs below the initial
freezing point of the food product. Most foods have a freezing point
that varies from −0.5 to −2.4 °C and, specifically for fishery products,
this parameter is between −0.8 and −1.4 °C.
◦ Super chilling is also a promising and eco-friendlier technology due
to an 18% reduction in environmental impact when compared to the
conventional cold chain. Additionally, it improves the overall quality
of food and extends its shelf-life by reducing microbiological
contamination

10. How is superchilling applied?
◦ Portuguese method:
◦ This method has been used aboard a number of Portuguese trawlers working in the warmer
parts of the Atlantic, and has also been tried on a German vessel. Each vertical pound division
in the fishroom is made of stainless steel and has hollow passages within it, through which
refrigerated brine is pumped. The shelves are also of metal and are spaced about 16 inches
apart, so that no part of the mixture of fish and ice on each shelf is more than about 8 inches
from a cold surface. In addition, refrigerated brine is pumped through pipe grids buried in the
insulation on the deckhead, the tank top and the ship’s sides. The brine temperature is
accurately controlled. In more recent Portuguese installations the fish have been stowed in
boxes between the metal shelves, in an attempt to overcome the difficulty of discharging a
mass of partially frozen fish.

11. ORIGINAL PORTUGUESE METHOD OF SUPERCHILLING:

12. SUPERCHILLED BOX STOWAGE:

13. SUPERCHILLED SHELF STORAGE: