Lab Cat

18 Oct 2006

Meat Preservation

Filed under: Chemistry, Food, Science — Cat @ 2:00 pm

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:

  1. hot smoking (50-85 oC) for less than an hour to several hours;
  2. warm smoking (25 – 50 oC) for several days;
  3. cold smoking (12 -25 oC) for up to several weeks.

Smoked foods include kippers[‡], smoked salmon (lox), ham and bacon, and sausages. Smoking can be added as a flavoring[§], but then it does not preserve the meat.

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.


Footnotes:

* 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.

 

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13 Comments »

  1. I hope that you shall not lose respect for me, but I am an ardent fan of beef jerky. My time in the American West has done this to me, as home-jerky makers sell their wares on the sides of mountain passes in the summertime. I never considered the chemistry of the whole process, though. Thank you for the education. Looking forward to discussing the chemistry of beer and wine with you sometime.

    Comment by Abel Pharmboy — 19 Oct 2006 @ 10:17 pm

  2. Beef jerky might be ok, but soy jerky is bleuh.

    Comment by Cat — 22 Oct 2006 @ 6:47 pm

  3. Agreed, soy jerky is pretty sad. Beef jerky varies widely in quality — I find most of the “supermarket” brands such as Bridgeford and Oberto oversweet and with poor flavor. (Slim Jims and the like are, of course, unspeakable. ;-) ) My favorite is the Japanese style. Japanese and Chinese markets also have a lot of other jerky meats and (especially for Japanese) various pressed and salted fish. (When I eat the shredded squid, my cat will *not* leave me alone! :-) )

    There is also a South African semi-jerky called “biltong” which I like. The preservation of this is probably interesting from your point of view, as the inside is pink and moist (though rather greasy). Nevertheless, it is stored at room temperature, traditionally in a paper bag.

    Comment by David Harmon — 28 Oct 2006 @ 1:25 pm

  4. I had forgotten about biltong. I’ll have to do some research and find out how they make it. If it is greasy, perhaps a fat layer stops oxidation.

    Thanks

    Comment by Cat — 30 Oct 2006 @ 9:22 am

  5. Thank you for this interesting post. I found it while doing a google search on the terms “preserving meat” + science. I am vegan and am attempting to make a vegan version of “corned beef” using seitan – which is a protein “dough” that is made from wheat. I am wondering if you can advise me on whether or not the protein strands from wheat will react the same way as protein strands in beef when allowed to cure in a brine? I am trying to decide if I should cook the seitan ahead of time and then try curing it, or really take the traditional route and cure it prior to cooking.

    I appreciate any advice you, as a food scientist, could give me.

    Thanks!

    Comment by Kreeli — 12 Jan 2007 @ 1:36 pm

  6. The protein of wheat and seitan is very different from that of meat so I don’t know how it would react to being left in a brine for a long time. It would probably soak up the flavors and may end up being very salty.

    I marinade tofu and that makes it more flavorful, but that is usually only for a couple of hours before cooking.

    You could always experiment and try brining before and after cooking and see which you prefer.

    Comment by Cat — 12 Jan 2007 @ 3:48 pm

  7. HI again and thanks for your response. Can you tell me what the difference are between animal protein and plant protein, wheat specifically?

    I have a lump of seitan “corning” right now and will be happy to share my results with you. The saltiness is of course a concern with any type of brining but I fully intend to rinse and soak the seitain thoroughly, then cook in a saltless broth, once the curing time is over.

    Traditionally beef is corned for up to a month. I am going to go for two weeks with the seitan and see how it fares. But I am still interested in knowing what makes some protein different from others. Is it the amino acids?

    Comment by Kreeli — 15 Jan 2007 @ 2:23 pm

  8. Kreeli

    I’ll have to write another post on the topic of proteins. Sometime soon! Thanks for the idea.

    Comment by Cat — 15 Jan 2007 @ 2:41 pm

  9. thank you so much!!! this helped me soo much!! keep up the good work!

    Comment by Bryce — 1 Nov 2007 @ 9:22 pm

  10. i am in the eighth grade and i am doing a science fair project on on “what preserves raw meat the best?” and i need to know how to tell if the meet is rotted or not, not just by the look and smell…and i obviesly cant taste it just in case it is rotten!..i have six peices of meat…1 in sprite, 1 in water, 1 in salt, 1 in vinegar, 1 @ room temp, and 1 in the refridgerator…what should i do!…i need a good grade and so does my partner!!!….please help!

    Comment by Hannah — 28 Dec 2007 @ 9:59 pm

  11. Hey there, I also got to do a project on meat preservation.

    Any tips???

    Comment by Shannon — 26 Jun 2008 @ 6:48 am

  12. im concerned with the dye they preserve the red meat in and how it breaks down in ur system like aspertine in diet soda could this b y ma ny people is sick

    Comment by ox — 26 Jul 2009 @ 8:17 pm

  13. Is this fact??
    If it is…tnx! It help me a lot f0r my rep0rt 2mrw…

    Comment by I am pretty — 27 Sep 2010 @ 12:24 am


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