Salting, Brining

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Salting,Brining

• FSN 661
• April 2009

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Salting

• Salting is an ancient and traditional method in
  many countries
• The principle is to reduce water activity (aw) of
  fish muscle to retard microbial spoilage and
  chemical reactions
• Salt passes into the muscle, and at about 6-10
  conc. in the tissue it will prevent major
  spoilage organisms

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Movement of water and salt
Diffusion of salt in
Salt
High Salt
Conc.
Water
Osmotic transfer of water out
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Effects

• Loss of water
• Limits bacterial growth
• Limits enzyme activity
• Increase of salt
• Limits bacterial growth
• May limit enzyme activity

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Grades of Salt

• Different grades of salt, from 80-99.9 purity
• Purer salt leads to less problems
• less contaminants, e.g. sand, dust, water,
  calcium, magnesium (slow salt penetration and
  leads to problems, e.g. water uptake, bitterness)
  
• less contamination with halophilic bacteria (salt
  tolerant)
• Some salts can have up to 105/g of bacteria

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Grades of Salt, cont.

• At least 95 purity should be used
• Impure salts have only about 80 NaCl
• Solar salt most impure (major source of
  halophiles)
• Can purify by washing briefly with water (calcium
  and magnesium dissolve sooner than NaCl)
• Finer salts are ideal for brines (dissolve
  rapidly)
• Larger size salt preferred during dry salting

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Impurities in salt

• Calcium and Magnesium salts
• Reduce the diffusion rate
• Absorb moisture from the air
• Bitter flavor
• Whiter cure (sometimes preferred)

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Impurities in salt

• Iron and Copper salts
• Surface browning and yellowing
• Accelerate rancidity

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Production of sea-salt

• Sea water is placed in settling ponds and the
  particulate materials are allowed to settle out.
• Evaporation concentrates the salts until the
  least soluble salts, calcium carbonate
  (limestone) and calcium sulfate (gypsum),
  crystallize and settle out.
• The water is then moved to a second pond.
• Further evaporation causes the sodium chloride to
  precipitate.
• After most of the NaCl has precipitated, the
  concentrated brine is drained off and the
  precipitated NaCl dried.

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Microbial growth

• lt 6 salt
• Halophiles cannot grow
• gt6 8 salt
• Normal spoilage bacteria inhibited
• 6 12 salt
• Some bacteria grow slowly (T)
• 12 - saturated salt
• Halophiles grow well

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Fish in saturated salt brine at 0.75
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Halobacteria growing in a salted pond
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Critical salt content
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Protein denaturation

• Above the critical salt content, there is rapid
  protein denaturation.
• Therefore, heavily salted fish cannot reach its
  original form / quality when re-hydrated.

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Mechanism

• Salt and water exchange occur at a front, when
  critical salt concentration is reached.
• This front moves from the surface to the center
  of the fish

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Methods of Salting

• Methods of salting
• Brine salting (270-360 g NaCl/L)
• Fish immersed in solution of salt
• Frequent stirring necessary
• Replacement of salt in brine may be needed
• Need to supply fresh brine to new batch of fish
• Dry salting (about 3-4 parts fish to 1 part salt)
• Salt rubbed into fish surface and fish left
  uncovered to dry
• Not recommended in tropical regions due to
  insects and rodents
• Insect/rodent parts and excrements (a.k.a
  filth) common in certain processed fish

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Methods of salting (cont.)

• Kench salting
• Alternate layers of split fish and dry salt
• Piled up to 3 ft high
• Extracted water is drained off
• Periodic re-piling
• Final salt content depends on
• Thickness
• Temperature
• Amount of salt

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Methods of salting (cont.)

• Pickle salting
• Same as above but pickle does not go away as fish
  are packed in water tight containers (at least 1
  meter deep)
• Pickle is from water and blood leaking from the
  muscle as salt penetrates
• Need about 30 salt for this to occur
• Salt brine injection
• Fish injected with salt solution and phosphates,
  then soaked in salt solution for 2 days (10oC)
  and then kench salted

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Mackerel being dry-salted
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• Process example (salted groundfish)

• Head, gut and wash fish
• Soak in 10 brine for 30 min
• Drain
• Dry salt fish in shallow boxes
• Stack fish up first one skin down, last one skin
  up
• Leave for about 12 h up to 30 days
• Wash salt crystals away with 10 brine or
  seawater
• Dry fish during day
• Pile fish up overnight
• Pack product

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Typical cod salting operation (kench salting)
Splitting the cod
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Salting the cod
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Maturation period in salt
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Drying the cod
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Drying fish the old way (still widely done)
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Rapid salting

• Boiled salted fish
• Fish fillets and salt are steamed in a pouch for
  2 hrs
• Drip is discarded
• More salt added and steamed for 2 more hrs.
• Pouch drained and sealed.
• Shelf life can be 3 months at room T
• Labor intensive, but product obtained in 1 day

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Rapid salting, cont.

• Bagged salted fish
• Transit and storage time is used to salt the
  fish.
• Raw fish placed in bag 16 parts fish, 6 parts
  salt, 2 parts water. Air expelled, sealed.
• Salting may not be uniform possibility of
  spoilage
• Accidental puncture causes total loss of product

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Rapid salting, cont.

• Dehydration Injection Salting
• Freeze-drying, then injection of salt brine
• Most rapid, and controlled method.
• Freeze-drying is expensive
• Timing of injection critical.

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Rapid salting, cont.

• Del Valle-Nickerson method
• Fish is ground in the presence of salt (20 100
  of the weight of fish)
• Product is pressed in a mechanical press
• The press cake is dried to 49 wb moisture (rate
  limiting step). The salt content after drying can
  be 22.6 wb.

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Rapid salting, cont.

• Anderson-Mendelsohn method
• Minced or ground fish mixed with excess salt (4
  parts fish to 1 part salt) in a brine.
• Free liquid is pressed out
• The press cake is dried.
• Brine minimizes contact with air, and reduces
  oxidation.
• If exposed to light the product may brown.

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Old Icelandic way
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Quality inspection and packaging
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Injection
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Distributing the fish
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2 day soaking period in salt
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Fillet sorting/grading and packaging
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Pickle salting
Late stages
Early stages
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• What influences the salting process
• Fish thickness -gt thicker slower NaCl uptake
• Fish fat content -gt more slower NaCl uptake
• Fish quality -gt older faster NaCl uptake
• Salt concentration and quality
• Temperature
• More rapid salt penetration as T is higher
• More chance of spoilage (normally in center of
  fish, turns into a smelly paste)

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Storage

• Keep cool, dry and well ventilated
• Have plenty of insect/rodent traps
• The saltier the product the longer the shelf-life

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Sliming

• Yellow or beige slime at the surface.
• Pungent smell
• Occurs at 6-8 salt (light slated)
• Require high oxygen levels
• Higher T promotes sliming

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Red halophilic bacteria

• Pseudomonas salinaria and Sarcina
• Indole and H2S production foul smell
• Salt is generally the source of contamination
• Wash with fresh water kills halophiles
• Higher T needed for growth (15 to 80 C)
• Keep T low.

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Dun

• Mold Sporendonema epizoum
• Optimum salt 10-15, T25 C
• Peppering of black, brown spots at the surface.
• Harmless but ugly.
• From surface to the interior through roots
• Requires min 5 salt. Wash with 0.1 sorbic acid.

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Pilot plant / lab

• See the salted fish
• Drain and salt again until Thursday
• Observe Thursday