Blood meal is bought on crude protein and ruined by temperature. Almost all of the material in circulation meets 88 – 92 % protein and delivers considerably less than the analysis promises, because the process destroyed the lysine, which is the only economic reason to include it in a diet. The dark colour and the strong smell come from the haem group and from the drying itself: they are no evidence of damage nor of quality, and anyone buying by nose is guessing.
| Component | Amount | Why it is there |
|---|---|---|
| Whole raw blood | 1,000 kg, 16 – 19 % solids | Total solids define the whole yield. If it arrives diluted with wash water below 14 %, you are paying steam to evaporate somebody else’s water and the cost per kilo of meal rises in proportion. |
| Free water to be removed | 810 – 840 kg | Four fifths of what comes in has to come out. Every kilo removed mechanically costs a fraction of what it costs evaporated, and any water reaching the dryer is extra thermal exposure time on the lysine. |
| Time between bleeding and processing | Under 1 – 2 h, or chill below 15 – 20 °C | Blood clots in minutes and ferments in hours. Past that time non-protein nitrogen rises: analytical crude protein does not fall, but the amino acid value does. Out of range the product is devalued from birth. |
| Direct steam for coagulation | 90 – 100 °C for 3 – 10 min | Precipitates the protein so it can be separated mechanically instead of evaporated. Below 85 °C the clot does not set and the fines go out with the effluent; with a long hold the cross-linking starts that lowers digestibility before drying. |
| Drained or pressed clot | 240 – 300 kg at 28 – 40 % solids | It is the only stream that enters the dryer. Every point of solids gained in the press is water that is not evaporated afterwards: less fuel and less time hot. |
| Separation effluent | 700 – 760 kg with 1 – 3 % solids | If the serum comes out deep red and above 3 %, product is being lost and the treatment plant loaded. It is the most common yield leak and the least measured. |
| Water evaporated in drying | 150 – 210 kg | It sets the thermal consumption and, above all, the exposure time. Evaporating slowly is exactly what destroys the lysine: the goal is to dry fast, not to dry gently. |
| Finished meal | 160 – 190 kg at 6 – 10 % moisture | 16 to 19 kg of meal per 100 kg of blood. Lower yields point to solids lost in the serum or shrinkage from over-burning; higher ones, to moisture out of control and mould risk. |
| Fat in the finished product | Less than 1.5 % | Blood contributes almost no fat. If it shows up, there is contamination with floor water, digestive content or condemned material, and with it comes microbial load and analytical variability. |
Closed trough or vacuum from the bleeding point, with no wash water. To process in under 1 – 2 h, or chill below 15 – 20 °C. The reason is biological: blood is a perfect culture medium and proteolysis starts before the truck arrives.
Injection up to 90 – 100 °C with a 3 to 10 min hold and enough mixing for the heat to reach the whole mass. The aim is to form a separable clot: you trade evaporation, which is expensive, for mechanical separation, which is cheap.
Decanter, screw press or centrifuge up to 28 – 40 % solids. Every point here cuts the dryer load proportionally. The setting is verified by measuring solids in the serum, not by looking at the cake.
Ring or flash dryer with inlet air at 250 – 400 °C, residence in seconds and product leaving at 70 – 90 °C. The key is not the air temperature but the time the particle spends hot and wet: that is the window where lysine blocking happens. A batch cooker at 120 – 145 °C for 2 to 4 h meets sterilisation and ruins the amino acid.
Down to ambient plus 5 – 10 °C before grinding and bagging; grind to a 0.85 – 1.4 mm screen. Bagging hot condenses water on the inner face of the bag and creates lumps and mould in a highly hygroscopic product.
Physical separation of raw and finished areas: air, augers, elevators, people, bags and forklifts. Salmonella in blood meal almost never survives the process; it gets in afterwards. It is validated by sampling, not by trusting the dryer thermometer.
Moisture 6 – 10 % and water activity below 0.60, dry warehouse and rotation. The iron in the haem group is pro-oxidant: stored next to fats or in already fatty diets, it accelerates rancidity.
No batch should be released on protein, moisture and ash alone. It is released against pepsin digestibility and against the ratio of available lysine to total lysine. That is the only pair of figures that separates a useful meal from expensive nitrogen filler.
| Control point | Value |
|---|---|
| Moisture | 6 – 10 %, with water activity below 0.60 |
| Crude protein | 88 – 93 % as-is basis |
| Fat / ash | Less than 1.5 % / less than 4 % |
| Total lysine | 7.5 – 9.0 % on product |
| Available lysine over total lysine | Above 85 % |
| In vitro pepsin digestibility | Above 85 % |
| Salmonella | Absence. Method, sample size and criterion according to the standard in force in the country of sale |
Half the craft is reading the defect. These are the ones that keep coming back.
| What you see | What caused it |
|---|---|
| It comes out black and hard, like charcoal, and yields less | Thermal over-exposure: recirculation in the dryer, high inlet air with irregular feed, or a dryer running empty. Stabilise the feed flow and control the product temperature at the outlet, not the air temperature. |
| It analyses 90 % protein but the animal does not respond | Cross-linking and lysine blocking: the nitrogen is still intact and that is why the analysis misses it. Measure pepsin and available lysine, and move the drying to low-residence equipment. Proximate analysis does not detect heat damage. |
| It cakes in the silo and forms lumps | Product bagged hot or with moisture above 10 %. It is highly hygroscopic and it condenses. Cool to ambient plus 5 – 10 °C and close down moisture and water activity. |
| Salmonella positive even though the process goes above 95 °C | It is not survival, it is later recontamination: shared augers, dust, unfiltered cooling air, reused bags, people moving through. Unidirectional flow, zone separation and validation by environmental sampling. |
| It smells of ammonia when the blood is received | Fermentation before processing. Crude protein does not fall, the real value does. Shorten the time between bleeding and coagulation or chill at reception; reject loads with perceptible ammonia. |
| Low yield and the serum comes out deep red | Poorly formed clot from insufficient temperature, poor steam mixing or an out-of-calibration decanter: the fines go to the effluent. Verify the real 90 – 100 °C in the mass and measure solids in the serum every shift. |
No. The haem group gives shades from dark red to blackish brown even in well processed product, and spray-dried material looks lighter because of particle size, not because of less heat damage. Colour and smell are not indicators of nutritional value; available lysine and pepsin digestibility are.
Physically yes, technically it is the worst decision in the process. Two to four hours at 120 – 145 °C with agitation meet sterilisation and destroy a large fraction of the available lysine. The result analyses 88 – 90 % protein and behaves like expensive nitrogen filler.
The limit is set by isoleucine, not by palatability. Haemoglobin is practically devoid of isoleucine and high in valine and leucine, which creates branched-chain antagonism. In practice inclusions are low and always with a digestible amino acid matrix; the exact level is defined in the full formulation, not by a rule of thumb.
Because proximate analysis measures how much nitrogen is there, not how much reaches the animal. Two meals at 90 % protein can differ by twenty or thirty points in digestibility depending on the dryer and the thermal residence. An 88 % that is digestible is worth more than a burnt 92 %, and it costs less in feed conversion.
Yes, it is a protein source with low rumen degradability. But the same overheating that blocks the lysine also makes it indigestible in the small intestine: it passes the rumen and leaves in the dung. The measure is still digestibility, not bypass.
Rendering of meat by-products: sterilisation at 133 °C, pressing, milling, typical protein, calcium and phosphorus figures, and Salmonella control.
Compound feedFormulating on digestible amino acids and not on crude protein: ideal protein, pelleting, plant controls and feed conversion.
FloursHow precooked corn flour is made: degerming, cooking, flaking, drying, milling, and the water absorption index that decides whether the dough works.
PetfoodHow extruded dog and cat food is made: formulation, extrusion parameters, drying, coating and reference nutrient profiles.
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