A History of Smoke Preservation

By Simon Krasemann

A History of Smoke Preservation
Foods have been preserved by smoke-curing since before the dawn of recorded history. People in all cultures the world over have relied on the smoke-curing of fish and meat products for long-term storage.

It is important to make a distinction between smoking for preservation, and smoking for texture and flavour. Today the former is common in less developed countries where transportation and climate extremes may be a factor. The later is popular in developed countries where refrigeration and an integrated logistical infrastructure for the efficient transportation of perishables is in place.

In its simplest form smoking meat and fish is similar throughout the world depending on the end product desired. Preservation can be accomplished by first cutting the flesh into thin strips and then drying them slowly over a fire — or in the sun in northern climes).

Packed as dried smoked products, these can travel great distances and remain edible for long periods of time. In all these processes, drying is of paramount importance for preservation, because it is moisture in the flesh that permits bacterial activity and spoilage. Salt accelerates the removal of water and hence its widespread use as a traditional perservative. Further, the application of extracts from the smoke (phenols, etc.) retards the development of spoilage bacteria. 
 
IN EUROPE AND BRITAIN DURING THE MIDDLE AGES various heavily smoked and salted foods were relied upon to carry people over the lean times of late winter and into spring. Fresh fish could not be transported any distance from the port of landing unless they were preserved. Two of these products were Red Herring and Salt Cod. Red Herring was made with heavily salted herring that was smoked for up to three weeks in a kiln similar to those in use today to make "bloaters" on Grand Manan, New Brunswick today.
These herring, used initially in the home markets, were widely exported (and continue to be so today) to the West Indies in the infamous "Triangle Trade" between Britain, its Northern Colonies and the West Indian plantations. While not smoked, Salt Cod supported the expansion of trade routes throughout the world, and is a prime example of how a simple product can be of supreme importance to merchants — and the extension of government policy.


THE RAPID GROWTH OF LOGISTICAL INFRASTRUCTURE (railways and steamships) beginning in the 1840's, enabled the transportation of perishables. For the first time in human history it was possble to move large quantities fresh fish from one place to another. This marks the beginning of sea-fishing industrialization. As a result of the widespread availability of fresh fish, the popularity of heavily salted, heavily smoked products — a mainstay for hundreds of years — began to decline. In the same period (mid 1800's), the smoked fish products we now regard as traditional came into being. These are mildly smoked and dried and contain minmum salt as condiment.
The kipper for example was invented by John Woodger at Seahouses in Northumberland about 1843 after considerable experiment. Within a few years it had become very popular and remains so today.

Where the primary reason for smoking fish had been formerly to preserve it, it was now mainly to impart a pleasant mild smoky flavour. Rapid transportation for foodstuffs meant a long shelf-life was no longer so essential.

THE MARKET FOR SMOKED FISH UNDERWENT A MAJOR CHANGE in the mid to late nineteenth century. And yet the actual technology of smoking fish remained much the same as it had been for centuries.
It was not until 1939 that the Torry Research Station in Aberdeen, Scotland developed the Torry Kiln that a reliable tool was generally made available to the industry. This mechanical kiln can be relied upon to produce a high-quality, uniform product time after time. The use of a forced-draft greatly enhances drying and smoke application and with the use of a heat source remote to the smoke generator a much reduced smoking time is achieved. This accomplishes two things; first, the fish is exposed to moderate temperatures (prime for bacterial growth) for a shorter period and secondly, the kiln-operator can process more fish in a given time and produce it at a consistently higher quality.
 
 
Many companies now produce kilns based on this proven technology of laminar air-flow through the product. The increasing use of micro-processors has added another quality factor that insures consistency and adaptability in processing any smoked seafood product for varying demands in any marketplace (differing salt levels, moisture content requirements, etc.).
On a personal level we have been asked if the application of all this technology removes us from the actual business of producing a really top-notch food. The answer is both yes and no. Yes, we don't have to baby-sit every load of fish now-it is controlled much more closely than any human could actually do it ourselves (people need breaks, holidays, etc.). The answer is no, it doesn't remove us from the process because the computer faultlessly carries out what we have programmed into it earlier. The result is as uniform and consistent as the changing nature of fish will allow.
 
 
The Physical Properties of Smoking Fish
IT TAKES FIRST CLASS FISH to make a first-class product. Like the old saying "garbage in, garbage out," a good product can't be made from stale fish. Some folks believe that smoking can cover up moldy or stale fish off-flavours. This is false. Any unpleasant odours or flavors will be readily apparent in short order.
 
 
Haddock Golden Cutlet
Given that the fish are of good quality and free from disease it is important to look at the natural condition of the fish. In the North-East, for instance, spring herring and mackerel are low in fat and make a poor quality product. Haddock that have recently spawned cannot be expected to turn-out well. Atlantic salmon with a fat content much in excess of 14% becomes too oily and can oxidize rapidly after processing.
Fish for smoking must be fresh and certainly post-rigour. Some keep longer than others. Trout for instance, will keep longer than mackerel which keep longer than silver-hake (given similar washing, handling, and icing) and so on. In short, get to know the fish your dealing with before you jump in and produce something even your dog wouldn't touch.

After preparation which may include, filleting, or nobbing, splitting or chunking, the fish is either brined or packed in fine dry salt (brining being more common nowadays). Once salted, the fish are placed in the kiln for a period of time and allowed to drip. This allows excess liquid to drain off and in certain products, allows the formation of an attractive gloss. The gloss is actually the drying of a water soluble protein and such a pellicle is the mark of a high-quality smoked whitefish like cod or haddock. Fatty fish will develop a gloss also, but this can be generated by the oil that comes to the surface during smoking. Fish packed in dry salt will not form a pellicle of the same nature. 
 

Most fish is cold-smoked, meaning no point will the temperature be allowed to exceed 34°C. Cold smoked products include: Lox, Haddock, cod and Kippers. Hot smoking on the other hand, is the slow raising of the kiln temperature to in excess of 60°C to cook the product. Seabright hot smokes: Mackerel, Shrimp, Scallops and Salmon. These products are generally flaky in texture and are ready-to-eat.

IT IS BEST TO CONSIDER THE TWO PROCESSES of smoking and drying separately, as controlling one does not necessarily mean controlling the other.

Smoke should be produced from a smoldering, saw-dust fire. Wood smoke is composed of millions of microscopic particles which rise like a fog, and by vapours. The fog is mostly water, carbon and trace solids. The vapour contains what we're after, namely volatile oils which are released from the wood and furnish the characteristic flavours and preservative qualities.

The choice of wood for smoking varies a great deal with geography. Most reputable smokers spurn the use of softwoods in favour of hardwoods (Oak in the United Kingdom; Alder on the West coast of North America). Experienced smokers also know that given a quality hardwood source, variations in species will result in only small flavour differences. So there is ample latitude to refine one's recipe! Some advocate the use of more resinous woods with oilier fish like mackerel to counter its strong taste. Softwood dust is sometimes added when smoking white fish to bring up colour more rapidly. A general rule of thumb would have it that if a piece of smoked fish tastes "pitchy" it has more to do with the temperature of the fire then the type of wood you use. 

At Seabright the exact formula for our wood smoke is a closely guarded. Yet everyone here knows we use native Nova Scotian hardwoods and over the years we've found ground juniper can be used with great positive effect.
A hot fire (blazing flames, little smoke and more complete combustion) actually tends to burn off the volatile oils and reduces them to more stable tar type resins. Pretty yuckey all round. So keep the fire down, cool and watch out for flare-ups. 
 

Drying

WHETHER DRYING OCCURS AND THE SPEED OF DRYING is influenced by a number of factors: the speed of the air-flow; the moisture content of the fish; the temperature and moisture content in the smoke; and most important; the relative humidity (RH) in the surrounding air.

Relative humidity is generally expressed as a percentage in relation to the temperature. Therefore if the RH is 100% at 20°C and you cool the air just slightly — presto it rains. Let's assume however, that the temperature is about 16°C at 75% RH. This air will not dry fish very quickly at all but, if we raise the air temperature to 30°C, the RH would fall to about 45%. An RH of about 65% at a temperature of 30°C, is about perfect for most climates (if possible). If the RH falls too far below this the fish will dry too rapidly and "case-hardening" can result. A high RH in excess of 75% will prevent effective drying from taking place.

Temperature and smoke should be controlled separately. We have seen that we need a cool fire but we need an internal kiln temperature of at least 30 to 35°C. How to achieve this? Generate the smoke "remotely" from the actual kiln and provide heat from either electrical elements or natural gas burners in the kiln. Sure people did, and do, generate both smoke and heat together but not if you are seeking a reasonable consistency. We don't want salmon that's to die for this week — and salmon that will kill you the next. Consistency will be hard enough to come by in any case. Don't worry about a boring product. If its good it won't be boring!
 
Kilns or "What can I smoke it in?"

AS MENTIONED, KILNS HAVE come a long way in a comparatively short period of time and there can be some confusion as to which would work best for you. First, consider what kind of fish you're smoking and what kind of product you want out. Cold-Smoking is the most difficult to achieve on a consistent basis so, if you're just starting out, I recommend Hot-Smoking. This gives a fully cooked product and can handle the greatest range of fish. Smoked Mackerel, Eel, Salmon, Sturgeon, even small Haddock and Cod can be delicious if hot smoked.

A simple Hot-Smoker can be an old refrigerator — or even a barrel can work reasonably well. Just make sure what you are using is clean. Clean sawdust from a cabinet-maker (NOT from a power-saw-it's got chain-oil in it!) or a local saw-mill. Get the finest "grind" you can. If the dust is too coarse the point of flame temperature may get too high and you'll wind up with a raging fire. Remember, a slow, smoldering fire is what you need. An electric hot-plate (to provide the heat required), an indoor/outdoor thermometer (this allows you to monitor the smoke temperature to ensure it comes up slowly and regularly), a few racks (stainless steel, or chrome-plated steel/brass will work fine but NO exposed brass, copper or other material that corrodes quickly or you could start ingesting some very undesirable elements).

 Years ago I used an old bucket with some heavy steel mesh over the top (to prevent "smuts" or ash from blowing onto your fish) and lit my sawdust in that. At the time I also scavenged the fan from an old computer and stuck that at the top to blow the smoke about a little. We would recommend sitting your kiln away from anything else that can burn (it wouldn't be the first time someone either burnt their house down or caught the woods on fire at the cottage doing this and it can really be a drag on the whole weekend!).

Process the fish. Keep plenty of notes, including times, weather, temperature (inside the kiln and out), salt/brining times and strengths (brine strength can be measured using a hygrometer available from a hardware store (car battery tester) or from a brew shop (measuring alcohol levels). They all do the same thing-measure the density of water so when you add water the density increases and it floats higher in the solution. 
 
Because liquids become more or less dense with temperature the above table is for use with water at about 60°F. After your first experiment. Cool the fish rapidly after it reaches ambient temperature. Sample the product yourself before you feed it to any anyone else. Keep everything VERY clean and disinfected. Most of your products will keep very well in a fridge (well wrapped) for about 10 days.