When it comes to eating raw fish, the first thing that typically comes to mind is how fresh the fish is. Many people believe that the fresher the fish, the better. While this is true to an extent, it’s also a bit more nuanced. Freshness is certainly crucial for both taste and safety when eating raw fish.
However, certain types of fish don’t necessarily reach the peak of their deliciousness when they’re extremely fresh. In fact, allowing the fish flesh to age for a few days—or even over a week in some cases—can enhance its flavor. Although aging fish flesh is less commonly known than aging meat, such as beef, mastering this technique can unlock new possibilities for elevating raw fish dishes beyond traditional sushi and sashimi.
Let’s explore the benefits and techniques of aging fish flesh.
What Does “Aging Fish” Mean?
When you age any flesh, whether fish or meat, a series of natural processes occur that enhance its flavor, texture, and tenderness. Here’s what happens during an aging process:
Moisture Loss
As the flesh ages, moisture slowly evaporates from its surface. This moisture loss concentrates the flavor, making the flesh taste richer and more intense.
Enzyme Breakdown
Natural enzymes in the flesh break down muscle fibers and connective tissue over time. This enzymatic action tenderizes the texture, making it more melt-in-your-mouth compared to fresher cuts.
Flavor Development
The combination of moisture loss and enzymatic breakdown creates a more complex flavor profile.
Fat Oxidation
The fat in the flesh also undergoes slow oxidation during the aging process, contributing to a more robust and savory taste. This controlled oxidation further enriches the flavor.
Texture Changes
As with everything else that dies, fish also undergo a period of stiffness, known as rigor mortis, after slaughter. Once rigor mortis sets in, the muscles contract, the fish becomes stiff and inflexible, and its texture hardens. Therefore, fish flesh is often very firm and chewy while it is very fresh. During the aging process, rigor mortis passes and the texture gets more tender.
Types of Aging
For meat (not fish), there are typically two types of aging methods:
- Dry-aging method: The meat is hung in a temperature- and humidity-controlled environment for an extended period, usually between 14 to 120 days. It leads to the most intense flavor concentration and textural changes.
- Wet-aging method: The meat is sealed in vacuum bags and aged in its own juices. It results in a more subtle flavor but still tenderizes the meat.
For fish, however, the Japanese traditional aging method is slightly different from above. It is somewhere between the dry-aging and wet-aging methods. Also, just like any meat-aging method, aging fish flesh has its risks. Therefore, you will watch out for several points explained in the sections below.
What Fish to Age and How to Pick Fresh Fish
Aging fish flesh can increase its flavor. However, the method is not recommended for all fish. It is often applied to white-fleshed fish, like red snapper and yellowtail. Blue-backed fish, such as horse mackerel and sardine, are not suited for the aging method. This is because they can create high levels of histamine that can cause a serious physical reaction when they are aged. Compared to red-fleshed fish, white-fleshed fish tend to have firm flesh with an almost crunchy texture and a lighter flavor. Thus, the aging method is a great way to enhance its umami flavor.
The first thing to remember is the fish should be fresh and of good quality for a good aging outcome. If the fish is already smelling fishy and its color is deteriorating, it is not meant to be eaten raw at all, whether aged or not.
Besides, if the color of the face has turned reddish, it is an indication of an old fish. The same coloration throughout the body and face means the fish is fresh. Some other features to check for fresh fish include clear eyes and bright red gills. Also, you want to choose a fish with a firm body. This is because the body gets softer, and the guts also become soft and start to smell as time goes by.
How to Age Fish Flesh Without Ruining It
Let’s take the case with sea bass. Firstly, remove the scales by scraping your knife vertically against the fish sideways. Then, cut off the head and remove the guts since that is the part where the rotting process first begins. The detailed steps about gutting are explained in one of the videos on our YouTube channel.
After removing the head and guts, you will see a white membrane behind where a lot of blood is found. Slice it open with your knife gently. Meanwhile, it is important to handle the fish with extra care as the flesh can easily get damaged by the knife during the process. Then, clean the fish with a brush while running water. At this point, you want to have the fish clean without any membrane or fat left inside.
After drying the fish with a towel or kitchen cloth, put a dry paper towel inside the belly to soak up any water or blood coming out of the fish during the latter aging process. Wrap up the entire fish in a paper towel for the same purpose and wrap it in saran wrap. Now, it is ready for the aging process.
The Process of Aging Fish Flesh
One of the essential factors for aging fish is temperature. Make sure to keep the temperature of the fish 1-2°C (around 34-35°F). The fish will go bad instead of aging above the appropriate temperature and will freeze below 0°C (32°F). A regular home fridge is typically set between 6-7°C (around 43-44°F). Therefore, to achieve a suitable temperature for storage, it is recommended to use paper towels and bags filled with cold water and ice cubes. By keeping the fish this way, not only can you eat the fish raw for the next 3-4 days, but the flavor will prevail.
You might want to check the condition of the fish every day. You can make a small cut and taste it. If the fish is aged enough and tastes tender, it is ready to use. If the fish is still firm, it needs another day or two to be rested. Then, you can go through the same procedure for storage. An important note is to change the paper towel daily while minimizing the contact of the fish with oxygen. This will help eliminate the odor.
Tips from Master Chef
Handling raw fish requires extra attention and care during the aging process.
For one, you should use bags of water and ice cubes to keep the fish in the fridge, placing one each under and on top of the fish like a sandwich. Make sure to add a paper towel between the bag and fish in both layers. This will prevent the fish from getting too much pressure from the water bag. Otherwise, the weight of the water will damage the fish.
Also, you may wonder if it is better to filet and age the fish or age the whole fish before fileting. If you want to store it longer, the latter option is ideal. This is because it slows down the aging process, extending its shelf life. On the contrary, most sushi restaurants filet fish first so that chefs can check and control the condition of the fish as much as needed.
Our Sushi Masterclass – Advanced- course teaches more professional techniques that are hard to find anywhere else.
Serving Aged Fish
The aging techniques enable the fish to increase both its flavor and tender texture, which is different from that of fresh fish. Some restaurants may apply their own methods to extend the storage period to even a few months. The longer the fish is aged, the more inosinic acid will be produced, giving the fish a unique moist texture.
The best way to serve aged fish with such features would be sushi or sashimi. This way, you can simply enjoy the flavor of the fish enhanced by the aging method. Check our blog post, Typical Sushi Menu – What to Include in Your Menu – for more information about sushi menu.
That said, that is not the only way to take advantage of its characteristics. Adding heat can significantly change the taste and texture of aged fish. Therefore, it can be cooked by grilling, frying, or boiling. In this way, you can enjoy them in various cooking methods.
Learn More with MJCA!
Despite its simplistic appearance, there is a world of depth to the art of sushi. Learning how to enhance the flavors of the ingredients used in sushi to the fullest extent possible is an excellent way to master the art of sushi. Exploring professional methods, such as the technique of aging fish, is also a part of the exciting journey of the sushi world.
If you wish to learn more about the technique and course in general, check out our Sushi Masterclass – Advanced- course tailored by our master chefs with years of experience in and outside Japan. This course is also available in our Grand Membership Plus, providing all of our current and future courses (a certificate or live sessions with a master chef are not included in the plan).
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