The brine depends on the delivery as well as the fish.

Put a shrimp brine and a fish brine side by side and they look like they belong to different industries.

A tumbling process may use a relatively dilute brine at a high liquid ratio, while injection may deliver a more concentrated brine in a smaller volume. The actual concentrations and volumes depend on the product and process.

Their objectives can be similar, but species, product format and the way the liquid enters the muscle all affect the formulation.

What both of them are for

For water retention, salt and functional ingredients need suitable distribution in the muscle. Their effects must be assessed through the intended freezing, thawing and cooking process.

Fish and shellfish muscle is poor at this to begin with. It is more delicate than red meat, it holds less water once the protein has been stressed, and it is usually frozen at least once between the vessel and the plate. A product that has lost water holding capacity gives drip in the pack, a dry bite on the plate, and a lower weight at every point in between.

So the target is the same in both cases: a defined amount of functional ingredient, evenly distributed, inside the muscle. Species, tissue condition and processing also affect the result.

Shrimp: short distances and external contact

A shrimp is small and thin. Nothing inside it is far from the surface, so diffusion is a realistic way of getting there. This is not true of a tuna loin.

For many whole-shrimp products, size and appearance make immersion or tumbling more practical than injection. Brine uptake depends on the tissue, formulation and the pressure, agitation and duration used.

In this example, two process features affect the concentration.

There is a lot of liquid. The shrimp sits in a large volume relative to its own weight.

There is a lot of time. The cycle runs for a long period rather than an instant.

Concentration, contact time and the liquid-to-solid ratio all affect uptake. The retained dose and salt level must be measured for the chosen process rather than inferred from those inputs alone.

There is a second reason for keeping it dilute. Shrimp is eaten as a whole piece and nothing dilutes it on the plate. Salt is perceived directly, and the margin between correctly seasoned and unpleasant is narrow.

Where permitted and appropriate, the bath may also carry a melanosis-control treatment. Its suitability and dose require separate validation.

Fish: delivery into thicker pieces

In a thick fillet or loin, diffusion alone may be too slow for the target process. Injection can shorten the distance over which ingredients need to distribute.

In an injection process, needles deliver liquid directly to the interior.

That reverses both of the conditions above.

The volume is small. Injection adds a modest percentage of the fish's weight rather than surrounding it in liquid.

Delivery is rapid. Distribution, equilibration and loss of injected brine can continue after the needle has passed.

For a given retained ingredient target, a smaller retained brine volume requires a higher concentration. Injection brines are not necessarily equivalent to tumbling brines, so concentration and retention both need to be established.

The number that matters is not the brine strength

This is the point at which the two processes stop looking like opposites.

What matters in both is how much functional ingredient ends up in the muscle, evenly distributed. The brine concentration is only one term in that calculation, and on its own it says nothing.

A specification written as a brine strength is therefore an incomplete specification. Written as a target in the finished product, with the process stated alongside it, it transfers between plants. Written as a percentage in the tank, it does not.

What happens when one is copied into the other

Copying either brine into a different process without adjusting the formulation can miss the intended dose.

A fish brine used in a tumbler may deliver excessive salt or functional ingredients if its concentration is unsuitable for the liquid ratio and contact time. Check salt level, texture and retained yield after cooking.

A shrimp brine used in an injector may deliver too little functional ingredient if its concentration is unsuitable for the retained injection volume. Acceptable initial uptake alone does not establish retention through storage and cooking.

Poor retention can be missed by weighing only at the end of the line and may become apparent in the pack.

Two problems that belong to each process

A concentrated injection brine may approach a solubility limit, and it is prepared and used cold. Anything close to saturation at chill temperature is one small change away from coming out of solution, and where it comes out is in the lines and the needles. Blocked needles give uneven delivery across the fillet, which is invisible until the product is cut or cooked.

A dilute tumbler brine is a large volume of chilled, lightly salted water, often recirculated. That is a reasonable growth medium and it contacts every surface of every batch. Its microbiological management is part of the process, not a side issue.

And yield only counts if it stays

Uptake is easy to achieve and easy to overstate. Water can be put into shrimp or fish without much difficulty, and it will be there on the scale at the end of the line.

The question is whether it is still there after freezing, after thawing and after cooking. Conditioning the protein network can improve water retention, but the amount retained through freezing, thawing and cooking must be measured.

Which is why the brine, the tumbling or injection process, the freezing and the cooking are one system rather than four steps, and why a yield figure quoted at the end of the line is not a yield figure.

If you are working on uptake, drip or texture in shrimp or fish, tell us what you are making and how it is processed.