Hot Boning In America
By Eben van Tonder
20 April 2020
When we formulate recipes, we formulate for:
- Protein content (according to legislation);
- Functionality of protein sources and gelling properties;
- Water Holding Capacity (which speaks to affordability);
- Mouth-feel, bite and firmness / tenderness;
- Freeze/ thaw stability where required;
- Visual appeal;
- Shelf life;
- Emulsion stability.
Hot boning is a technique where practitioners claim that water holding capacity is high, without the need to use phosphates. In emulsions made from such meat there is no need for non-meat extenders, emulsifiers and stabilisers. The processing is also achieved without the need for expensive and unnecessary refrigeration. It can have a material impact on shelf life by extending it and renders the end product firmer with a better visual appearance. It is therefore worth a proper consideration.
Hot boning is when bones and fat are removed from the animal carcass within a few hours after slaughter, before chilling. Some researchers distinguish between hot and warm boning. We will get into these differences at a later stage.
A short and clear description of hot boning is given by Dr. Lynn Knipe, who is, amongst other things, responsible for the processed meats extension programs at Ohio State University and conducts research related to the quality and safety of processed meat products.
Dr. Knipe writes that “the fresh, “bloom” color of meat is enhanced with rapid chilling (using CO2) of pre-rigor meat, as soon after hot boning as possible. This improvement in color can be reflected in a sharper particle definition (less smeared look), as well as a leaner appearance. While there are other functional advantages to hot boning of meat, currently, the main commercial reason for pre-rigor boning of pork is to extend the shelf life (time until the lean loses color) of the fresh color. Other advantages to pre-rigor processing include a firmer texture to the final cooked sausage, with less cooking loss.” (Knipe)
Schematically, the difference between hot-boning and cold-boning is represented as follows:
A German friend who is a 3rd generation Master Butcher tells me that his dad never used emulsifiers or stabilisers in his fine meat emulsion, and his secret was hot boning. Well, it was not really a secret – it was practiced throughout Germany.
Let’s briefly look at the ingredients normally used in sausage production. We will consider them by listing protein content and the relative price of the different proteins. This will show that when formulating products, a proper evaluation of the different ingredients is required.
In the table below I give the relative protein %’s of different functional ingredients and the Rand price as it was in April 2020. The links attached to this paragraph title and title below in the table are live and you can download the spreadsheet and insert the price of these protein sources in your own currency. You can also adjust the protein % of the particular product you use. The manufacturer must be consulted to get this information. The final protein % will depend on the particular product blend and the production method used.
|Protein options in formulating recipes (Mellett)|
|Protein Source||Price in SA (Rand)||% Protein||Rand/ kg Protein|
|Soya / TVP||14.00||48%||29.17|
If you do not know that pork loin typically contains 20.85g of protein per 100g of meat (20.85%), you can calculate it as 0.8kg of lean meat (in a 80/20 trim ratio) to get to the % lean that is 0.8 (% lean) / 4.8 = 16.7% protein. It follows from the formulas below.
-> Remember the key equations:
%N x 6.25 = % Protein
% Protein x 4.8 = % lean
6.25 x 4.8 = 30
So, %N x 30 = % lean (Mellett)
The red and blue raw materials show the difference between high and low-end products.
-> High-End and Low-End Products in South Africa
Local food legislation invariably calls for a minimum protein percentage and usually specifies what the source of the proteins must be. The hybrid meat formulations in South Africa usually contain a mixture of the ingredients listed in blue. High quality sausages or loaves or hams are produced in South Africa from either primal cuts (whole muscle) or from the ingredients listed in red. The question is if hot boning is used and all the costs are taken into account, including labour, energy (refrigeration and cooking), is it possible to come close to the price point when low-end products are produced, again, taking every input cost into account.
-> Hot Boning – A way to Make High-End Products Affordable
Hot boning is of interest for its Water Holding Capacity and its ability to form stable emulsions without the need to add non-meat fillers, stabilisers and extenders and the firmer texture and visual appeal. Due to the availability of data from the USA, it makes it easier to trace the history of the development of the technique from there.
Early work on Hot Boning in America
The Des Moines Register reported in 1974 on the work of Dr. R. L. Henrickson of the Oklahoma Agricultural Experimental Station where he had been working on hot boned meat since 1965. His initial work was on pork, and later he included beef in his research. Henrickson says that the concept was conceived by his research team in 1957. He is quoted as saying that pork from this process is “equal or better” in quality compared to conventional methods. It is interesting when he says that “we are fast approaching a time when social and economic pressures will force the implementation of new meat processing procedures.” (Des Moines Register, 1974) Such conditions have existed in many parts of the world for a long time.
Status of Hot Processing of Meat in the United States
Arguably one of the foremost authorities on hot boning, Dr. Henrickson writes that “there appears to be very little direct industry application of hot processing of primal cuts in the United States, even though most research evidence points to many advantages for the various available processing systems.” In contrast to this, “the success of the pork sausage industry can be attributed directly to the short processing period from slaughter to the chilled or frozen package. The system makes raw seasoned sausage available to the consumer in less than 90 minutes after slaughter. This process not only takes advantage of economics in processing and chilling, but provides the consumer with a sanitary, longer shelf-life product. The major bulk of the raw pork sausage industry now uses pre-rigor pork.” (Henrickson, 1983)
“The raw pork sausage industry uses young sows with the proper ratio of fat to lean. This careful selection of the animal makes it possible to blend a product without a great amount of excess fat.” If sausages are made, the following steps are followed.
-> Sausage Production
- Separate the lean meat and fat from the bone;
- Chopped into uniform pieces;
- Cool it, partially;
- Add spices / seasoning;
- Stuff into one and two pound grease-proof casings.
- Cool down “using an ethylene glycol bath system.
- Another option is to extrude the pork sausage links with or without casing directly onto a liquid nitrogen enclosed endless belt. “By the time each link reaches the end of the belt it has absorbed sufficient refrigeration to be case frozen.”
- Packaged and tempered to 0 deg F / -18 deg C for marketing.
-> If Not All the Meat is Used Immediately
Pork tissue (lean and fat) which can not all be used for sausage production immediately are handled as follows.
- Salted (2-4 percent) during the following procedure of . . .
- Coarse chopping of the meat
- Place in 50-60 pound / 20-25kg boxes and freeze.
- The pre-salted meat is used in sausage manufacture because of its ability to yield myosin for binding.
There is a variation on the above system which is commercially appealing, namely to produce the slabs of coarse chopped meat with spices and fat or rind emulsion already blended in. I have seen this widely in use in India and Nepal and my intention is to test these methods and create a product which can be exported to small scale butchers who lack the equipment or experience to create the emulsions.
Hot Boning and Some Chilling
Pre-rigor pork has been demonstrated to have many benefits. In America it is a matter of preference. Dr. Henrickson writes that “the prospect of cutting hog carcasses directly from the dressing line prior to chilling makes the average packing house worker shudder. The reason most often given is that one cannot trim hot cuts to presentable standards of appearance.”
Dr. Henrickson argues that the attitude in the US against hot-boning due to appearance is invalid “since most of the primal cuts do not require a high standard appearance value. All pork cuts except the loin and spare rib are subjected to some manner of forming either by can, package, stockinette, casing or press. Therefore, the only primal cut which may require some form of smoothness is the loin. Smoothness of the loin can even be attained by leaving the back fat intact, conveyorizing the loin through a blast chill and then trimming. A few minutes in a blast chill at -50°F / -45 deg C should provide ample firmness for the necessary trim. An alternative would be to market a completely boneless loin, since the consumer is now discriminating against fat and bone. The whole concept of hot processing not only requires converting practices of plant and market, but the thinking of personnel.” (Henrickson, 1983)
Henrickson reports that there has been progress during the past thirty years and expresses the hope that the process will be widely adapted in the future. He says that “even though the pork industry has been reluctant to adopt hot processing for primal cuts, it has reduced the period from kill to package. High volume (880 hogs per hour) ham production (kill to can in three days) has been practiced since 1965. Pickle solution is automatically injected into the meat and the cure is equalized in a matter of hours. A flexible vacuum wrapper makes the product ready for shipment and distribution in less than three days. Hot processing could reduce this time by an additional day.” (Henrickson, 1983)
There is a widely held belief that microbial problems are a major drawback to the system of hot boning. There is evidence that hot processing could provide a more sanitary products. (Henrickson, 1983)
These claims were further investigated by Fung, et al. (1981) who found that if “hot-boned meat is chilled adequately (from carcass temperature to 21 C with 9 h) during the first 24 h, the hot-boned meat is acceptable in color and odor and bacterial quality after 14 days of storage and 3 additional days of display. When meat is not chilled adequately (from carcass temperature to 21 C at 12 h), the shelf-life and storage life will not be acceptable.”
Their research showed the need for adequate chilling after boning the hot meat “at a rate sufficient to produce a bacteriologically acceptable product.” Boxing the meat before chilling is, according to their data, doable, but should be approached with great care. They caution against too-rapid cooling rates of hot-boned meat which can lead to cold-induced muscle shortening, which, in turn, causes toughening of the meat. (Fung, 1981)
They claim that faster chilling rates of up to 3-9 h after fabrication can be used as an additional insurance for better microbial quality and still the processor will be able to avoid cold-induced toughening. They also add that electrical stimulation can very successfully be used in conjunction with hot-boning, as an extra measure to prevent muscle toughening. They therefore recommend “chilling hot-boned meat to 21 C within 3-9 h after fabrication, and with continuous chilling, to below 10 C within 24 h.” (Fung, 1981)
Another way to prevent cold shortening is to select bigger carcasses with more fat. The smaller and leaner carcasses are more susceptible to cold shortening due to the reduced fat cover, which results in the deep areas chilling faster. This results in tougher products. Apart from carcass selection, this can be overcome by introducing a conditioning step (semi-hot boning) of 4 hours more until rigor has occurred (in beef it can take 24 hours or even longer). To reduce the time for rigor to occur, electric stimulation is used immediately after slaughter. It must however be reminded that in pork, cold shortening is not such a big problem because postmortem metabolism in pork occurs faster.
Generally speaking, hot boning can even double microbiological shelf life due to the fact that surface bacteria have not had time to grow before antimicrobial salts are added. Even if the meat is slightly tougher, in comminuted meats this is not a problem because a higher ultimate pH is achieved (what we achieve with phosphates in South Africa). Because of the higher pH there is an increased water holding and emulsifying capacity, which will yield a product that is juicy and of superior quality. Pre-rigor meat also acts as an oxygen-scavenger. It removes residual oxygen from inside the package after closure, resulting in a long shelf-life.
This does not mean that micro should not remain a major concern in hot or semi-hot boning. There will be an increase in moisture on cutting surfaces and great care must be exercised to prevent this becoming a vector for microbial contamination and growth.
In hot boning, it is easier to remove fat from the warm cut. Care must be taken to maintain a juicy product with flavour, brought out by the fat. It will be important to reduce fat variability rather than cause it to increase. (Fung, 1981)
Summary of Benefits of Hot Boning Compared to Cold Boning
Ockerman and Basu from Ohio State University reported the following benefits of Hot Boning compared to cold boning.
- Higher meat yield (1.4%)
- Labour savings (20%, faster – 4 mins / carcass) (with the right equipment to hold carcass still and pull muscles downwards)
- Less weight loss during chilling (1.5% less)
- Less purge in a vacuum package (0.1 – 0.6%)
- More uniform products
- Darker colour
- Reduced refrigeration space (50 – 55%)
- Lower refrigeration cost (40 – 50%)
- Shorter processing time (40 – 50%)
- Lower transport cost (primals vs carcasses)
- Superior water holding capacity
- Higher emulsifying capacity
(Dikeman and Devine, 2014)
- Shape distortion of cuts because the bone is removed;
- Reduced flexibility in production;
- Stricter hygiene requirements;
- Increased temperature control;
- New cutting procedure;
- Retrofitting of traditional cold boning area;
- Retraining or hiring new cutting personnel;
- Possible reduced tenderness because of cold and rigor shortening;
- Alteration of colour;
- Accelerated micro growth.
(Dikeman and Devine, 2014)
In the USA, hot boning is used mostly by whole-pig fresh sausage processors who use hot boning and rapid salting.
Rigor Complex Formation of Actomyosin
With the onset of rigor mortis, ATP disappears from the muscle. In the absence of ATP, actin and myosin combine to form rigor complex of actomyosin (Kamejima, et al., 1982) Willi Wurm, Master of Meat Science and Processing put it in terms that I can understand. In private communication he said that “actomyosin has to be separated again during a sausage emulsion process, by adding phosphate. Only separated Actin and Myosin have the capability to make an emulsion with fat and water. With hot boning methods you can keep the Actin and Myosin separate, when you grind the deboned meat and add salt. After that you cool or freeze the meat or process. The Actin and Myosin remain separate, and you can process without phosphate. You can also vacuum pack whole muscle pieces before the postmortem process and wet-age it. It will be classified better than normal wet-aged beef meat. Be careful to store the warm packed meat for the first night outside the fridge on tables and then refrigerate the next morning for 4 weeks.
Oscar Mayer was the first to apply hot boning to a large commercial operation. They used it to process packer sow hams to be used in sausage manufacturing. (Dikeman and Devine, 2014) The weight of these sows, which is “owned by a packing plant”, therefore packer sows, is between 110 and 140kg.
After the initial publication of this article I received fascinating comments from around the world.
We also have developed and patented the technology with which to process beef without exposing the spinal cord. A huge advantage for BSE. NO BONE MEAL AS WELL. Labor savings as much as 30-50%. We will soon be taking a 3 day industry standard of kill floor to truck down to 1 day.” For those of you who are interested, Gary can be contacted at NSCbeef@yhaoo.com, 117 Land Grant Lane Baird, Tx 79504 325-665-0602 Cell 325-518-5038.
Another person (still awaiting permission to use his name) recalled that “all the American processors were using hot boned meat, also went to a company called Marjacks who were producing a lot of further processed products, not sure if they are still going but would be a good source of information as would Wayne Poultry as they had an incredible set up for hot deboning.”
Not everybody had such a positive experience with hot boning of beef. Someone (awaiting aproval to use his name) said, “I used to do a bit back in the 80s not great for presentation or yield. Hot Beef Boning, selling vac packed into wholesale. Very fast, but poor yields and doesn’t do much for cutting quality. We soon stopped it.”
I have never been exposed to hot boning. The South African Meat Safety Act of 2000 (ACT No. 40 OF 2000) stipulates that meat must be cooled to a core temperature of 7 deg C before dispatch. Paragraph 40 (1) reads as follows. “A chiller used for chilling warm carcasses, sides, quarters or portions must be capable of providing uninterrupted cooling to reduce the core temperature of the meat to 7 def C before dispatching.” According to this definition, it seems as if hot boning can be done as long as the bond meat reaches the required 7 deg C temperature before dispatch. I will take the matter up with a meat inspector.
In Germany, hot boning was widely used. Gero Lutge, the third-generation Master Butcher I was talking about in the introduction, sent me the following account of his dad’s use of hot boning. he writes, “in the earlier years my dad went to the local abattoir on Monday morning to slaughter the amount of pigs he pre-ordered. Then he loaded it onto his bakkie (pick up) in half pigs. Had a Schnapps and a beer at the tavern on the abattoir premises and went back to his butchery to immediately brake the pigs, debone them and prepare them for the week ahead. The meat trimmed for emulsion processing was immediately processed with a lot of ice so still not cooled down. The only additive he added was curing salt and spice. Even if he filled the emulsion a day later, the water intake and binding was tremendously higher than with phosphate when the pH level of the meat decreased overnight in the chiller.”
I am sufficiently intrigued to at least test pre-rigor meat for sausage production and legally there may be a way to do it even in South Africa. The motivation will be to simplify the process by removing the need of the 2-4% addition of extenders, stabilisers and emulsifiers. I am motivated by the comparison made by Ockerman and Basu from Ohio State University between cold and hot boning where they clearly and persuasively show the economic advantages of hot boning.
There is every reason to look into this very carefully!
Dikeman, M., Devine, C.. 2014. Encyclopedia of Meat Sciences. Second Edition. Academic Press.
The Des Moines Register Sun Mar 10, 1974 (Active link to article)
Fung D. C., Kastner C. L., Lee C-Y., Hunt M. C., Dikeman M. E., Kropf D. H.. 1981. Initial Chilling Rate Effects on Bacterial Growth on Hot-Boned Beef. Journal of Food Protection, Vol 44, July 1981.
Henrickson, R. L.. 1983. Status of Hot Processing of Meat in the United States. Oklahoma Agricultural Experiment Station, Animal Science Research Report.
Kamejima, S., Ishioroshi, M., Yasui, T.. (1982) Heat Induced Gelling Properties of Actomyosin: Effect of Tropomyosin and Troponin, Agricultural and Biological Chemistry, 46:2, 535-540, DOI: 10.1080/00021369.1982.10865074
Knipe, L. https://meatsci.osu.edu/node/127
Mellett, F. Private conversations.