According to Science Notes, “Osmosis is the movement of solvent particles (usually water) across a semipermeable membrane from a dilute solution to a concentrated solution.
The solvent dilutes the concentrated solution until concentration is equalized on both sides of the membrane.” Diffusion is the movement of solvent and solute particles from an area of higher concentration to lower concentration. At equilibrium, the net effect is a homogeneous concentration throughout the medium.
How does this relate to fishing? Salmon eggs for bait can be cured by using osmosis—and the same goes for salmon eggs for human consumption, better known as caviar.
How To Process Fish Roe
There are many ways to process fish roe. Common recipes often use borax, brown sugar, or non-iodized salt. Typically, those recipes are for curing chunks of pre-cut roe with the skeins, which is messy and sticky. An alternative is to use roe bags, with single salmon eggs.
How To Store Salmon Eggs
The best way to toughen up single salmon eggs is to obtain them from a ripe female salmon, store them in a bag with river water, and mix in some milt (the sperm-containing fluid) from a male salmon. Upon fertilization, a change will occur in the membrane. After the roe is fertilized with salmon milt, the membrane of the egg toughens and is ideal for making single-egg roe bags. These eggs are tough and survive being mixed in the river gravel without breaking. It is important to note, however, that the eggs will collapse and break if punctured.
If a male is unavailable, remove the eggs from the female salmon and store them in a Ziplock bag with river water. You can then cure them at home.
You can also create single eggs by removing them from a nearly mature skein for separation. The skein should be laid skin down and placed on a smooth surface (I prefer parchment paper). Gently pull the eggs off the skein with a spoon at the edge of the skein. After that, soak them in the water and then rinse them to remove any blood. The eggs will be soft and partially collapsed, but will not be punctured. They are very delicate, and you will lose some during this process.
What is Viral Hemorrhagic Septicemia (VHS)?
According to the Washington Invasive Species Council, “Viral Hemorrhagic Septicemia (VHS) is a deadly fish virus and aquatic invasive species that attacks and weakens the blood vessels of fish. Broken blood vessels and severe blood loss ultimately cause death. It afflicts more than 50 species of freshwater and marine fish in several parts of the northern hemisphere.” The source of the disease is uncertain, but it was first found in European freshwater trout in the 1930s and showed up on the west coast of Canada in marine trout and salmon in 1988.
VHS-free salmon roe received from Centerpin Angling® can be stored for years if unopened. Roe can be used immediately by anglers to make roe bags once it has been opened. In the curing process, the roe has been dehydrated. Once exposed to the river water, they expand and emit a scented white milt. If you tie the roe bags loosely, the eggs will be able to expand. I prefer salmon and steelhead roe sacs for salmon and steelhead from the bigger rivers on the west coast of British Columbia. I like the roe to be firm and bouncy so we can cast hard and for a long distance. This is the time when osmosis will become your best friend— when rehydrated in brine, the roe from Centerpin Angling® will separate into single eggs.
Brine Recipe For Single Fish Eggs
A brine for curing roe at its maximum salt content will still contain some undissolved salt. At least 1/8″ of the salt will remain visible on the bottom of the jar. Gently place the single eggs into the brine. If they are stuck together, don’t worry, they will separate on their own.
This is when the magic happens: They will swell (rehydrate), and the egg membrane will toughen up over the next 24 hours. Upon completing the osmosis process, their membrane will become substantially firmer to the point where the eggs will even bounce off the floor. Don’t penetrate them, though, as they will collapse.
Some anglers have their own brine recipe and add colour or scent to their curing process, while I prefer keeping the brining simple by using only salt.
How to Make Caviar
Osmosis is also a major factor involved in producing caviar. It is possible that your catch (roe) is already available as singles, which saves you time. Most often, however, they are still intact in their skeins. If you want to separate the skein, you can scrape it gently over a screen. Laying the skein skin down on parchment paper and gently removing the eggs with a spoon is my preferred method. If there are any loose particles on the eggs after you separate them from the skein, you should gently rinse them to remove them.
Unlike curing salmon roe for bait, making caviar from your own caught salmon roe involves less salt and less aggressive processes. The salt must be completely dissolved in the brine, and the cure time for roe is usually only one or two hours, depending on the salt content of the brine and your taste. Removing all the brine after the cure has been completed is important. Caviar should be stored in airtight canning jars and kept in the refrigerator for no more than a week.
Ikura Recipe (Cured Salmon Roe)
One of my favourite recipes has a very light taste. It is known as Ikura in Japan. Bonito is mixed with sake, sea salt, honey, and low-sodium seasoned soy sauce. With a delicate taste and a soft membrane, the roe will explode with flavour. While eating fresh for up to one week is your best bet, it is possible to freeze caviar for longer storage—I fill a canning jar with roe up to the maximum capacity before popping it into the freezer.
Be sure to label your salmon roe with species type and date of processing. The defrosting process needs to be slow, so remove it from the freezer and place it in the refrigerator to thaw. As a result of the membrane being frozen and then thawed, or perhaps because it has aged, the roe has a little firmer, crunchy texture. You will not experience any degradation in taste and quality.
Caviar is great way to get a good dose of “Vitamin Sea”—I hope you enjoy it as much as I do!
This article appeared in Island Fisherman magazine. Never miss another issue—subscribe today!