Notes on Fat Emulsion and Lecithin

  • Notes on Fat Emulsions and Lecithin
  • 17 October 2020
  • by Eben van Tonder

Shortage of beef body fat necessitates us to look to alternatives.  Brings up the general topic of fat emulsions.

An alternative and a much cheaper product is beef kidney fat.  It is, however, too hard and needs to be mixed in with body fat (a softer fat). A smoother fat will be created.  Kidney fat also has a less desirable mouthfeel.

General Emulsion

Fat Emulsion Recipe

Kidney fat 2
Body fat (other) 1
Binder and water 3

Note on Binder

Binder + water 3
Binder 0.5 + water 2.5 

Fat Emulsion Procedure

Temperature is all important in the process. 

Equipment preparation

Warm the equipment up by running hot/ boiling water through before you start working. The process is extremely sensitive to heat.  Cold equipment pulls the water temp down too quickly.

  • Remove water and put boiling water (at least 80 deg C) into cutter/ emulsifier.
  • Add binding agent first.
  • Gradually adds fat.
  • Gradually add fat until smooth.
  • Rest overnight in chiller

Fat Emulsion Results

This should yield a firm fat emulsion the next morning to mince.

Additional Considerations

  • For better mincing, use a binder with better structure or add fibre
  • When doing the total emulsion, reduce temp to – 5 deg C. better mincing and binding.

What is There is No Body Fat Available?

Add pork skin.

Alternative Beef Body Fat Recipe

Kidney fat 5
Skin 2
Binder + water 3

Alternative Beef Body Fat Procedure

Warm bowl.
Put boiling skin into cutter/ emulsifier
Add boiling water
Add emulsifier
Add kidney fat

Alternative Beef Body Fat Notes

  • Skin must be extremely soft
  • Try not to use acid. Make soft by boiling
  • Acid makes skin rubbery
  • Acid residue also spoils emulsion
  • Cook longer if you leave out acid
  • Pressure cooker reduce time

General Notes

  1. More lecithin is better

In a study by Weet et al. (1994) it was found that “the viscosities of emulsions might be expected to be directly correlated with the amount and quality of the surfactant used as the emulsifier. For example, the viscosity of emulsions prepared with 0.1 to 2.5 g thermalized granular lecithin increased from about 1800 cps to 14,000 cps (Figure below). Stability to gravitational settling increased with increasing emulsifier content where essentially no settling was observed after several days (Figure below).”

2. Thermalized lecithin’s (granular, liquid and gum) vs non-thermalised and gum lecithin.

Weet et al. (1994) also found that “the viscosities of emulsions prepared with thermalized lecithins were indeed substantially higher than those prepared with the corresponding non-thermalized lecithin’s. Emulsions prepared with thermalized granular, liquid and gum lecithin’s were 153, 61 and 200% higher than those made with the corresponding non-thermalized materials, respectively (Figure below). In another example, it took 20 times more liquid lecithin in an emulsion for a viscosity that was approximately the same as that prepared with 0.5 g thermalized liquid lecithin (data not given).”

Incorporation of Soy in Pork and Chicken Skin Emulsions in Cooked Sausages.

“Pork or chicken skin contains around 55% water, 35% connective tissue (mostly collagen), around 5–10% fat and 0.5% ash. Emulsions made of chicken or pork skin are widely used in cooked sausage production as they are inexpensive and add bite and firmness. Tendons or ligaments are also used for the same reason, and all these raw materials are very high in connective tissue and therefore collagen. When heated, collagen turns into gelatin and so contributes to a firmer bite, snap and texture.

It is very important that the raw materials for skin emulsions are treated and stored properly to keep the bacteria count low. They can be frozen and then thawed before being processed into an emulsion. The term ‘emulsion’ is not fully correct in this instance as, firstly, no fat is added directly and, secondly, any fat present is in a solid, and not liquid, form.

Skin or tendon emulsions can be made in different ways and each method has advantages and disadvantages. The two main options are to make an emulsion with non-treated material, or to use material that has been treated before being turned into an emulsion. The raw untreated skin, primarily chicken skin for this method, is cut with water and soy protein generally in a ratio of 1:4:4, where 1 kg of soy protein (predominantly soy isolate) is cut with 4 kg of iced water and 4 kg of skin. The soy protein is cut with cold water for around 2–3 min until a gel-like material is obtained. Cutting takes place under the highest knife speed possible and the knives used should be as sharp as possible. Chicken skin (mostly minced) is added to the bowl cutter and the total mass is cut at high speed until a finely cut mass is obtained with the maximum temperature being around 10–14 °C. Slightly frozen skin and some ice are used to prolong the cutting time, ensuring that a fine paste is obtained. The finely cut paste can be passed though an emulsifier afterwards to increase smoothness of the emulsion which is not often practised as cost is added to the material owing to the additional processing step. Salt (and nitrite) is used to extend the shelf life of the emulsion and is added at the end of the cutting process and mixed in gently. The shelf life of this type of emulsion is between 3 and 4 days stored at 0–3 °C. This is the simplest and quickest method of producing a skin emulsion, but all the water present is immobilized by added protein. The collagen present in the skin does not hold, or immobilize, any added water. Another method makes proper use of collagen to immobilize added water. By adding double-sour phosphates in conjunction with a small amount of soy protein, chicken and pork skin can be extended by around 80–90%. Thus 100 kg of skin can be turned into 180–190 kg of emulsion. Around 10 g per kilogram of total emulsion of sour phosphates and soy protein is added to the bowl cutter once cutting of the skin has started. Iced water, and some ice, is gradually added afterwards while cutting under a high speed. The principle behind this method is that the collagen starts to swell through the addition of sour phosphates and water is absorbed into the triple-helix structure as the result of swollen collagen (see Chapter 1, Section 1.3).

With this method, collagen immobilizes all the added water, and the small amount of soy protein is only added to emulsify the usually small amount of fat attached to the skin. This type of emulsion can also be passed through an emulsifier to obtain an even finer paste, and salt can be introduced at the end of the cutting process as well. This method uses well-chilled or even semifrozen skin to obtain a low temperature right from the beginning and the addition of iced water, or some ice, means that the cutting period can be longer. The amount of soy protein added to emulsify the fat connected to the skin (normally pork skin) is typically 0.5–2%, and is calculated according to the total mass (skin + water or ice).

The advantage of the above two methods is that the emulsion can be made directly without prior treatment of the materials and therefore labour costs are low. The disadvantage of these methods is that the final emulsion obtained is not as fine and creamy as that obtained from treated skin.

Chicken and pork skin can also be treated by placing them in a sour solution overnight. The soaking solution is prepared from a blend of different food acids and water, with the blend of food acids showing a pH of around 1.5–1.8. This liquid blend is mixed with cold water, with a 3% solution generally used for soaking chicken skin and a 5% soaking solution for pork skin. A stronger solution is required to treat pork skin because the collagen in pork skin has a higher number of cross-links than the collagen in chicken skin. This is largely because a pig is much older at slaughter than a chicken. Pork skin from sows cannot be treated successfully because the extremely high number of cross-links in the collagen molecules prevents proper swelling during soaking.

During soaking, the collagen starts to swell and water is effectively bound in the swollen collagen. Soaking results in a soft texture, making the skin easy to cut and hence resulting in an extremely fine and creamy paste when passed through an emulsifier. After overnight soaking under chilled conditions, chicken skin can increase in weight by between 70% and 90% and pork skin frequently shows a gain in weight of between 50% and 70%. Pork skin from pigs which were flamed during the slaughtering process to burn off remaining hairs tends to take up less water during soaking, with the amount depending on the degree of burning. The skin is washed thoroughly afterwards with cold water to remove excess acid from the surface. The washed material is then drained and often placed on trays and put in a freezer to reduce the temperature. Once it is well chilled, or even slightly frozen, the skin is placed in the bowl cutter and cut under high speed. Around 1% of soy protein is added to emulsify any fat present. Ice may also be added during cutting to obtain an extension of around 90–100%, based on the weight of the untreated skin. As an example, if 100 kg of chicken skin gained 90 kg (90%) in weight during soaking, around 10 kg of ice can be added in the bowl cutter to obtain 200 kg of emulsion. For pork skin, a final extension of around 190% is the norm. Salt (around 1.5–2%) and nitrite can be gently mixed into the emulsion once cutting is finished. The final temperature of a skin emulsion produced in this way should not exceed 15 °C, and processing semifrozen material prolongs the cutting process. Nitrite is not added if the skin emulsion is going to be used in non-cured products. This type of emulsion can be stored for 3–4 days at 0–3 °C.

Skin emulsions can also be stored in the freezer, and the finished emulsion is placed in trays in layers not higher than 10 cm so that the temperature of the emulsion falls quickly. If the layers are any thicker, cooling takes much longer and there is a risk of bacterial growth. Frozen skin emulsion is placed in the chiller the night before use so that it is not too hard to process.

Another method of making pork skin emulsion is to cook the skin first and then to cut it with water and soy protein in a ratio of 1:4:4. This method is not sensible from a technological point because collagen is denatured on cooking and loses its ability to hold water and to form a gel. Precooking the skin also represents an additional manufacturing step, which involves time and energy.

Beef ligaments can also be turned into an emulsion and the procedure is the same as for pork skin, soaking the ligaments in a 5% solution. Once again, a low bacteria count is vital because the water content of the final emulsion is extremely high. When no bowl cutter is available, the soaked, washed, drained and semifrozen materials can be minced with a small blade and placed into a paddle mixer. Around 1% of soy and around 1.5–2% of salt protein is added and the materials mixed well before being passed through an emulsifier once or even twice, to obtain a fine and creamy paste.

Other materials rich in collagen, such as the material obtained after putting lean meat through a separation machine to obtain soft MDM can also be turned into an emulsion. The collagen material obtained from the production of soft MDM, or by using a separation device during mincing, generally has a certain percentage of lean muscle tissue. Such collagen-rich material can be cut in the bowl cutter and around 20–30% of ice can be added. Additives such as phosphates are introduced at around 3 g per kilogram of total mass, and salt at around 18–20 g per kilogram of total mass. The term ‘total mass’ refers to the collagen-rich material and the ice together. By processing material obtained from soft MDM, well-chilled collagen-rich material plus 50–70% of the total ice and all phosphate and salt are cut at high knife speed for a while. The remaining ice is added once the temperature of the mixture reaches around 4–6 °C, which reduces the temperature back to around 0 °C. Cutting at a high speed continues until the temperature increases back to 12–14 °C. This produces a fine paste, which can be used for all types of emulsified sausage. A similar emulsion can be obtained by cutting the mixture until the temperature reaches around 6–8 °C in the bowl cutter and then passing it through an emulsifier.” (Feiner, G.. 2006)

Further Reading

References:

Feiner, G.. 2006. Cooked sausages, Chapter 12. Meat Products Handbook. Practical Science and Technology. Woodhead Publishing Series in Food Science, Technology and Nutrition. 2006, Pages 239-286

Weete, J., Betageri, S. Griffith, G. L.. 1994.   Improvement of lecithin as an emulsifier for water-in-oil emulsions by thermalization. July 1994. Journal of the American Oil Chemistry Society 71(7): 731-737. DOI 10.1007/BF02541430