In my freshman food science class I have been lecturing about meat chemistry. I find this challenging, but not because I am vegetarian. Meat chemistry is complex and preserving meat brings even complex chemistry; mostly because there are so many different methods of preservation. In addition, protein chemistry is not really my specialty. I am far more interested in carbohydrate chemistry.
What we refer to as meat is generally animal muscle, which is mostly water, protein and fat. Even after cooking, most meat products are about 50% moisture so it is a great growing media for micro-organisms. So the main problem with meat, poultry and fish is how to preserve it from microbial spoilage. Ideally, we could just slaughter the animals on an as need basis. It is rare, however, to eat a whole carcass so soon after slaughter to avoid having to preserve it.
Since some of the methods used to preserve meat by removing or limiting the water availability, this post counts as part of my series on water. The water limiting methods are drying, salting, and smoking. Other methods include pickling, jellying, lye, freezing, canning, refrigeration, vacuum-packing, and modified atmosphere packing.
Drying is probably the oldest method used for preserving anything. It works by removing water and, therefore, preventing microbes from growing. For meat, it is important to have water moving from inside the muscles to the outer surface where it evaporates, without a crust forming on the surface. If a crust forms, the internal tissues stay moist allowing anaerobic bacteria growth, which in turn causes spoilage. This can be prevented by reducing the thickness of the pieces of meat being dried so that there is a high surface area to volume ratio. The final moisture content should be around 3 -10%.
The loss of water causes muscle to shrink and become firmer. There are changes to the flavor and taste as fat is oxidized. If too much oxidation takes place, the fat will go rancid causing off-flavors. Jerky is the commonest form of dried meat which is not the most pleasant way [*] to consume anything, especially meat. Dried meat is also used in soup powders. Dried meat products can also be rehydrated.
Curing is at least two processes in one, salting and smoking. Meat is salted by either dry or wet curing. Dry curing is when salt is rubbed onto the surface of the meat and wet curing is when the meat is left soaking in a 15-20% brine. Sugar and spices can also be added to affect the color and flavor. The meat is preserved in sugar or salt and nitrates or nitrites. As well as reducing microbial growth through osmotic effects, the sugar, salt and nitrate/nitrite are antimicrobial agents.
According to Berlitz et al [†] low salt concentrations (less than 5%) cause meat to swell and higher concentrations induce shrinkage. Meat retains its natural color because the loss of water actually concentrates the myoglobin, which causes the color. Nitrites and nitrates preserve the color.
Smoking is usually associated with salting – uncured meat is rarely smoked. Smoking causes the moisture content to drop up to 40% and compounds in the smoke have antimicrobial effects. Some compounds in smoke are antioxidants, so smoking protects the fat as well as preventing microbial damage. Smoking has to be carried out at temperatures high enough to prevent microbes from growing but lower enough to prevent the meat from cooking and becoming tough or burnt. There are many different techniques, but typically these are divided into:
- hot smoking (50-85 oC) for less than an hour to several hours;
- warm smoking (25 – 50 oC) for several days;
- cold smoking (12 -25 oC) for up to several weeks.
Just for information on the other preservation techniques:
Pickling typically reduces the pH by cooking the meat in vinegar. It is the original way that corned beef was prepared – now it is also canned after preservation keeping it even longer. Using lye is how Lutefisk is made and preserves the food by increasing the pH. Jellying or aspic is converting the connective tissues to gelatin by cooking for a long time and then using the resulting jelly to preserve the meat. Jellied eels are popular in the part of London where my mum grew up – though I never did find out if she has ever tried them.
* So I am biased. I have never eaten jerky. It is not common in Britain and I have been vegetarian longer than I have lived in the States. Oh, I tried soy jerky – have you? Bleuh!
† It was frustrating trying to find information on what happens to meat during the preservation process. So I worked my way through all the food chemistry textbooks I could find, eventually finding the required information in Belitz, Grosch and Schieberle (2004) Food Chemistry (3rd Edition) p597.
‡ I don’t know what it is about kippers – a traditional English breakfast – but just the thought of them makes me want to go home and eat kedgeree, or visit Whitby’s smoke houses. Also I still find it hard to resist smoked salmon. [Mum, that doesn’t mean I’ll eat it when I come home.]
§ For example, you can use liquid smoke.