Exudate from Fresh Meat and Bacon - Key Bacteria Food and Possible Formation of White Spots on Dried Bacon/Meat By Eben van Tonder 15 May 2023
Any person who works with fresh meat is familiar with the reddish exudate that comes from any fresh meat cut. I have recently been confronted with white exudate from bacon post-heat treatment. I have been in the meat industry for 15 years, most of this time spent on bacon. I am too familiar with the white exudate that forms in the pan upon frying. Towards the end of shelf life, sometimes this white exudate appears in the vacuum packets.
In an amazing week, these different forms of exudate came into focus in their relationship to micro growth and weight loss. The different exudates were evaluated by Sheard (2001) in their work “Factors affecting the composition and amount of ‘white exudate’ from cooked bacon.
Micro and Fresh-Meat-Albumen
In the old literature, the exudate from fresh meat was called albumen. In my work with Richard Bosman on nitrite-free curing, we have learned the importance of peptones which is liquid protein as bacteria food for starter cultures. Albumen is therefore an ideal bacteria food.
While I was contemplating how to “harvest” the albumen, I made contact with an exceptional entrepreneur and butcher who invented a tray to fit into meat crates to separate the meat from the albumen as early as possible. The invention was based on many years of personal experience where he carefully noted the effect of albumen on microbial activity and managed to infer a direct linear relationship.
E. Mostert had a micro analysis done on this simple method where they analyzed fresh beef, ostrich, pork and chicken (whole and pieces) along with a variety of spices (unspecified) in the validation of the method.
E Mostert analyzed meat in its albumen after 24 hours at ambient temperature. The meat was placed on a drain tray and samples were sent for analysis 24 hours later and held at ambient temperatures. The results are reported as “after drain.”
These astounding results indicated the power of albumen (liquid protein) as a bacteria food. It was supported by Richard Bosman and my own work on cultivating bacteria which we rely on to convert L-Argenine in the meat protein into nitric oxide to cure meat. In our case we did not want to remove the micro from the meat – we wanted to enhance their metabolism by feeding them.
As far as pathogens are concerned, the Western Concept of limiting TVCs on meat provides us with a simple method for extending the shelf life of meat products by simply separating the meat from any exudate at every step of processing. The relationship between micro and albumen has been confirmed by Sheard (2001) both for fresh meat and processed meat.
An interesting case was recently brought to my attention where white spots were reported on high-injected bacon logs, post-curing and heat treatment. I suspected it was a sarcoplasmic protein. Richard Bosman was interested in identifying at what temperature albumen would change to white.
He harvested albumen from fresh pork and at 40 deg C it changed to white in colour.
The albumen was removed from the water at 60 deg C, but the colour change to white took place at 40 deg C. This means that protein-rich albumen that is on the outside of the bacon log will change into white spots on the meat in high-injected, high-salt bacon logs.
A food science professional who asked me to remain anonymous tested such white spots on meat for micro and found the TVC count on the white spots to be many times higher compared to the surface of the meat that did not have white spots. It was this report from private conversations, along with the results from the drain tray and Richard and my experience with peptones (liquid protein) as the primary food for bacteria that completed the picture for me of the linear relationship between fresh meat exudate and par-cooked exudate as in the case of high injected and tumbled pork and surface micro activity. The implications to shelf life and hurdles against micro contamination are vast!
When thinking about the basics of the Wiltshire system, the albumen is a key feature in the overall system. It is the liquid protein exudates from freshly injected meat that provides the basis for bacteria food.
Sheard (2001) confirmed the protein to be a sarcoplasmic protein and by comparing albumen (pork drip) with other forms of exudate, the high protein content is confirmed.
Exudate from Fresh Meat vs Bacon
Shread (2001) discuss the nature of the exudate. “One might anticipate that the exudate from bacon would differ from that of pork since the addition of salt, either dry or as a brine, is often used to solubilise meat proteins (for example Jolley & Purslow, 1988). Actin and myosin are the major protein components of the myofibril, comprising about 70% of the protein in muscle (Jolley & Purslow, 1988). However, only trace amounts of actin and myosin were evident at the positions where one would expect to find these two proteins. The exudate from cooked bacon, thus, contains less actin and myosin than the ‘sticky exudate’ that is produced during the manufacture of reformed hams (Jolley & Purslow, 1988).” (Shread, 2001)
“Previous work has shown that myosin is irreversibly denatured when meat blocks were exposed to high concentrations of sodium chloride (5M or about 29% NaCl) (Dilber-Van Griethuysen & Knight, 1991), resulting in minimal protein extraction (Callow, 1931). Dilber-Van Griethuysen & Knight (1991) argued that such salt concentrations could pertain during curing, immediately following injection, when there would be localised areas of high salt concentration, followed by a slower equilibration. This could account for the alternate light and dark bands (tiger-striping) sometimes seen in sliced bacon (Voyle, Jolley, & Offer, 1986) and
provides a reasonable explanation for the virtual absence of myosin and actin in the bacon exudate examined” by them. (Shread, 2001)
What is the origin of the white exudate from cooked bacon and ham? Shead (2001) offers the following suggestion: “Having identified the composition of the exudate, it is of interest to consider how the exudate is formed during cooking. Elevated temperatures result in the denaturation of myofibrillar and connective tissue proteins (Bendall & Restall, 1983) and shrinkage of the myofibrils, the main water compartment in muscle (Offer & Knight, 1988a). This results in the expulsion of water from the myofibrils, with weight losses of about 20–30% depending on the cooking method and type of bacon, and a consequent shrinkage in the dimensions of the product. In bacon, a large proportion of the water (65–90%) is lost by evaporation because of its large surface area; the rest is manifest as fluid, containing a small quantity of protein together with any liquefied fat. In the case of bacon, the fluid also contains salt. The proteins, derived from the sarcoplasm, are mainly low molecular weight and readily soluble. Heat denaturation of these proteins causes them initially to coagulate, entrapping some water and salt, conferring the typical appearance of the white exudate associated with cooked bacon. Further cooking results in evaporation of water from the exudate and a concentration of the solid material, which eventually darkens and burns onto the surface of the pan or grill.” (Shread, 2001)
Tempering and Exudate
A surprising result from Shread (2001) is the increased exudate associated with tempering. They concluded that their “results suggest that the partial freezing of meat, necessary for the high-speed slicing of bacon, increases the amount of exudate produced. It is well known that freezing increases the amount of drip in pork — typically double that of unfrozen pork (Offer & Knight, 1988b) — and since approximately 60% of the water would be frozen at -7 Deg C, even in bacon with 2–3% salt (Sheard, Jolley, Katib, Robinson, & Morley, 1990), this result is not surprising. The precise mechanism is unclear but it is known that freezing has marked effects on the structure of muscle. Freezing results in the formation of large columns of ice crystals outside the muscle cells and a consequent dehydration and shrinkage of the muscle fibres; these re-swell on thawing in a time-dependent fashion (Offer & Knight, 1988b). Thus, freezing has marked effects on the structure of the main water holding compartment in meat (the myofibrils) and the state and location of the water.” (Shread, 2001)
Chemical Reasons for White Spots on Bacon/ Freshly Injected and Heat-Treated Meat
We have given exudate as a reason for white spots on freshly injected meat, but are there other possible reasons? Dr Jeffrey Savell gave the following list of possible reasons for white spots on jerky.
“Mold — The white film could be mold on the surface if the product is packaged where oxygen can get to the surface (i.e., packaged in a jar, or non-vacuumed bulk pack), not vacuum packaged, nor backflushed with nitrogen. Mold requires oxygen to grow and will not grow if oxygen is excluded from the product.
Salts or sugars — If too much salt or sugar is used in the brine/marinade formula, then when the product is dried, these ingredients concentrate and at a critical moisture level crystalize on the surface of the product. Brine formulations yield about 9 to 20% ingredients in the dried jerky product. Those products that have above 10% ingredients tend to have more problems with film formation. Usually, this is caused by the extra sugar that is added, but not always.
Tyrosine crystals — Tyrosine, an amino acid, may be the problem. Just as tyrosine crystals form in cheese as it is dried, they can form on the surface of meat also. Usually, this occurs more on the sliced surfaces of country-style hams and a solid white film that looks like slime or mold, but is actually tyrosine. I have no suggestions for solving this problem.
Sodium nitrite — Some processors have reported that sodium nitrite precipitates on the surface of jerky if “hard” water with excessive amounts of iron is used to formulate brine. This would appear as a white film and would be rare, but possible.” (Savell, 2013)
This gives us a good list of suspects if we find white spots on recently prepared injected and heat-treated meat. The comment about the reaction of NO2– is interesting.
Calcium and magnesium are often constituents of hard water. When the content of calcium carbonate is too high in water, it reacts with nitrites in commercial curing brines to form calcium nitrite, leading to the formation of visible spots on the bacon when dried. These spots are typically white or off-white in colour and can appear as irregular deposits on the surface of the bacon. Not only the nitrites, but when phosphates are used magnesium and Sodium Tripoli Phosphates can react to form magnesium tripolyphosphate. Likewise, calcium can react with Sodium Tripoli Phosphates to form magnesium tripolyphosphate. Both these products appear as white crystals. White spots on bacon form, therefore, when hard water is used as a reaction between magnesium, calcium and nitrite and phosphate ions.
Micro control begins with limiting the exposure of meat to exudate (albumen). Pork exudate during the cooking of high-injected meat has the potential of causing white spots of high microbial activity on bacon logs.
Chemical reactions between the constituents of hard water, nitrite and phosphate can react to form white spots on dried bacon as well as dried meat such as jerky and biltong.
The relevance of microbial migration into meat comes in that surface bacteria are the major problem before injection because the injector needles push bacteria which are found on the meat surface into the meat. The drain tray is a brilliant way of preventing microbial contamination during processing. See Bacterial Migration Into Meat
Savell, J, (2013), Possible causes for white film on beef jerky, originally prepared by Dr. Jimmy T. Keeton.
Sheard, P. R., Taylor, A. A., Savage, A.W.J., Robinson, A.M., Richardson, R.I., Nute, G.R. Factors affecting the composition and amount of ‘white exudate’ from cooked bacon. Meat Science 59 (2001) 423–435