Rigor Mortis @ EU Regulations

Walking in any fish market, most people look at the eyes of a fish to survey freshness, or they open the gills to check the color. Yes I am interested in checking the eyes and gills as a precondition but more than that. While all these are all good signs to check but not enough to satisfy an expert, and I carefully survey the fish’s overall condition, ask questions and then make a decision.

Walking in Capri, I pass restaurants with fish displayed, and all vendors try to insist that their fish is fresh. Often they think so, without understanding much about fish, fishing or what effects fresh at the time it is caught, or even before while in the water. How fish are damaged when caught in nets, or on a long line, or not cared for correctly has an immediate impact on the fish’s quality. It baffles my mind to think that fishermen still net fish, because it is amongst the worst fishing techniques.

I was talking with a two star Michelin chef this week, he complained how local fishermen destroy the worlds best tuna catches in southern Italy by rolling the tuna on deck. I talk more and more about this phenomena, it comes up with chefs the more I consider selecting fish, as a main course, or evening to try it raw.

When buying fish, think about these factors for fish next visit to the fish market. By examining the fish you should expect the following;

Skin: Bright, iridescent pigmentation, no discoloration, and transparent.
Eyes: Convex (bulging), Transparent cornea, Black and bright pupil.
Gills: Bright color and no mucus.
Flesh: Firm and elastic with a smooth surface.

In Japan, most fish are handled with precision and care, a basic standard in their country. In fact, any fish in rigor mortis is not a suitable grade for sushi, and remains unsuitable for any restaurant with a good standard. In the rest of the world, most chefs have no idea about what I am speaking about. In Europe, it is a regulation to freeze any fish intended to be served raw to minus freezing temperatures. The regulations in Europe are regulated by regulation 853/2004 of the European Parliament and of the Council of 29 April 2004, on the hygiene of foodstuffs establishes an obligation for operators selling raw, or almost raw, fish products to subject the products to freezing at -20ºC for at least 24 hours. You can read about raw fish and parasites here: http://www.aesan.msc.es/en/AESAN/web/cadena_alimentaria/detalle/anisakis.shtml

So what happens to fish after they are hauled into the fishing vessel? If it is commercial, the crew is often not educated well enough, their habits are to get the best catch, discard the rest at the expense of the sea. Little do they know about handling the fish. The temperature of the whole fish as it goes into rigor can have a marked effect on the amount of gaping, which is flaking of the fish’s meat; the higher the temperature when it goes into rigor, the greater is the rigor tension and the weaker the connective tissue becomes. Thus the higher the temperature the more the flesh will gape.

Furthermore, with fish there are a critical temperatures and on deck above 17°C, contractions become so strong and the connective tissue gets so weak that the tissue breaks down completely, resulting in a fillet so ragged that it is completely unacceptable.

Fish in smaller vessels are treated more or less the same way unless the fishermen are using a long-line, and understand the effects of temperature. On a side note, the seas in and around the Amalfi coast are very deep and rocky. The depths are up to and more than 1500 meters, so fish get a good safe haven.

Immediately after death of any fish, the muscle is totally relaxed; a limp elastic texture usually persists, where after the muscle will contract. When it becomes hard and stiff the whole body becomes inflexible and the fish is in rigor mortis. This condition usually lasts for a day or more and then rigor resolves, the taste changes depending on how the fish is handled, e.g. temperature.

The issue of rigor mortis is not rigor mortis but more about the “point of death”, a time when the fish’s supply of oxygen to the muscle tissue is interrupted. At this point, the blood is no longer pumped by the heart, or circulated through the gills where, in the living fish, it becomes enriched with oxygen. Since no oxygen is available for normal respiration, the production of energy from ingested nutrients is greatly restricted, the fish gets very stiff!

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So here it all begins, the method Japanese use for stunning and killing the fish also influences the onset of rigor. Stunning and killing by using hypothermia, where the fish are killed and slurred in iced water. There is debate about this technique and how it influences the quality of rigor mortis. The significance of rigor mortis is of importance when the fish is filleted before or in rigor. In rigor the fish body will be completely stiff; the filleting yield will be very poor, and rough handling can cause damages.

Muscle tissue in the state of rigor mortis loses its moisture when cooked and is particularly unsuitable for further processing that involves heating, since heat denaturation enhances the water loss. Obviously the loss of water has a detrimental effect on the texture of fish muscle.

The stiffness in the muscle tissues begins to decrease owing to the enzymatic breakdown of structural proteins (i.e., collagen) that hold muscle fibers together. This phenomenon is known as “resolution of rigor” and is a decomposition, which can continue for days or weeks in a process, referred to as aging.

So in the end do we age fish, the answer is no, and it isn’t similar to red meats that improve with aging. I know, it isn’t as easy as it looks, if you think about sitting in a restaurant, you wouldn’t really understand what you are eating.