Sunday, January 19, 2014

Cold Shortening

This time of year you might think cold shortening is a result of men joining the Polar Bear club but it is really something else. Cold shortening is the result of chilling a carcass too soon after slaughter. Most folks don't realize the amount of things that need to take place right after evisceration to create the maximum amount of tenderness in meat.
 First I'll do my best to explain what cold shortening is without getting too technical. When an animal is slaughtered the system for transporting oxygen to the cells shuts down, obviously. This causes pumps that move adenosine triphosphate (ATP) to shut down and allow calcium ions to
bind up proteins, all at the cellular level. This is part of the process of rigor mortis. If the carcass is chilled too fast, this condition is magnified, resulting in muscle contraction that shortens muscle fibers, making the meat tougher. Think about it, when you get cold you shiver and your muscles tighten up. Its not exactly like that but sort of. Also, there are natural enzymes that kick in after slaughter to break down and loosen muscle fibers but a cold shortened muscle will remain tougher and never achieve the tenderness levels of a properly chilled carcass. Hanging a carcass allows for some muscles to be stretched which minimizes cold shortening for some muscles.
 Preventing cold shortening can present problems for a processor. To prevent it studies show that the fresh pre- rigor carcass ideally should be kept at a balmy cave like temperature of 60F 16C for about 10 - 16 hours.  A large beef plant wants to move thousands of animals through each day can't wait quite that long so many will speed up the process by applying electrical stimulation to the carcass. Zapping the fresh carcass depletes much of the glycogen energy that would allow cold shortening to happen. I saw this at a Cargill plant years ago. It was like "CLEAR" and bam, the whole side of beef twitched. Another trick is to add a calcium chloride solution into the carcass which increases the activity of the endogenous enzymes, the enzymes that break down meat when it is aged.
 The old method of slow chilling was much more haphazard. If a carcass has a lot of exterior fat, a poor yield grade 4 or 5, the carcass will naturally chill slower, resulting in more tender meat. I can remember picking out hindquarters of beef with my dad in the markets on 14th street in NYC and he would always look for the extra fatty ones. They cost us more but the quality level was always much higher so we could charge accordingly. Plus we would buy an old bull carcass for lean beef to mix in the fat trims for our grind. That meat was tough like a shoe but perfect for grinding.
 I recently talked with John Jamison from Jamison Farm in Latrobe PA and he confirmed the 16 hour rule for keeping a carcass warm for the first part after slaughter. The USDA allows him to keep the carcass at this warm temperature for longer than what is considered normal. He says the quality of the carcass is greatly increased. Most of his production is with lamb but he has experimented with lean grass-fed beef also, with great results. It is a delicate balance between tender meat and food born illness. If a processor wants to allow a carcass to chill slowly they need to be diligent in keeping the process as clean as possible.
 Another factor that can effect cold shortening is the condition of the animal when it is alive. A calm animal that has had no food for 24hrs but not starved will be less likely to have the condition than an animal that is aggravated or stressed.
 One other experiment has been done to change the muscle structures pre-rigor. We normally hang a carcass by the gambrel on the back leg. This stretches certain muscles guaranteeing they cannot develop cold shortening. But what if we hang the carcass in different positions? This would allow for the stretching of muscles typically allowed to shorten. This opens the door for small processors to do some custom things. It is very difficult for a large processor to change the way they hang carcasses because everything is geared to the chain speed and equipment used to break down everything.
 A bit of history also. Farmers that slaughtered their own meats often did it in the fall when the temperatures would range from just above freezing to about 60F. An old timer that knew what they were doing would slaughter on a warm morning and hang the carcass for a few days in the barn with the temperature slowly lowering. Perfect condition for tenderizing.
 A friend of mine shot a deer this fall just when the weather turning a little warm. He typically hangs it for about a week before I cut it for him. He was worried about the warm temps and I told him to relax, he did and so did the muscle structure of his deer. It was one of the most tender wild caught meat I've ever worked with.
 So as the temperature once again plummets this week keep in mind not to cold shorten, leave that to the polar bears.

3 comments:

  1. Hi Chef !
    Great website !
    I would like to know the difference in "Pure Blood" and "Cross Bleed", in cuts of Pork.
    Thank You ! Chris Kridakorn-Odbratt in the Jungle in Laos.

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