Optimizing Feed Milling Process to Control Mold Growth

Mold growth in feed can occur in the field as well as during the processing and storage of finished feed in the supply chain. To prevent it we need to have knowledge of their growth in different stages of the value chain starting from the harvesting of grain to the final consumption of finished feed. Feed processing in the feed mill is an important area where we can reduce and control the growth of mold to a large extent. But unfortunately, I have seen many feed mills are not focused on maintaining proper processing and storage guidelines and it results in unexpected mold growth and thereby poor bird/animal performance. So, let us understand critical areas in the feed mill to control it. Following are the essential requirements for mold growth in raw material and feed:
1. Nutrients in feed
2. Moisture
3. Temperature
4. Oxygen in the air
The presence of the above factors at a favorable level induces mold growth. The climatic condition prevailing in South Asia is highly suitable for mold growth during the majority of the year. This leads to a lot of losses in the value chain. The feed miller’s responsibility is to prepare and maintain storage and production SOP (Standard Operating Process) in the feed milling process to prevent mold infestation. The following practices can be followed in poultry and cattle feed production facilities:
1. Proper Storage Practice of Raw Material and Finished Feed/Product
Raw material can be stored in a warehouse or in a silo in the feed mill. Each option needs separate SOP and management practice. A volatile market and uncertain availability of raw materials lead to an increased tendency of feed millers for long-term storage. Silo is an effective way for long-term storage, especially for maize.
Maintain proper storage plan with clear demarcation of material at their allocated location in case of warehouse storage. Maintain FIFO (first in first out) principle for material usage. The bin card system is a very effective way of managing it, especially for raw materials. Protect storage bags from rainwater. Fumigate insect-infected raw material, if required, as insect infestation enhances mold growth. Keep proper stacking of material with a minimum 2 feet gap between each stack and from the wall for proper ventilation. Special precautions should be taken for finished feed stacking in the feed mill. An 8-10 bags stack is preferable based on the season. Keep finished feed on plastic sheet/pallet. Monitor and record the quality of stored material on regular basis.
2. Maintaining Desired Processing Parameters
Following process parameters need to be monitored, recorded, and maintained as per SOP
a. Temperature
Monitor temperature of feed during feed processing stages like conditioning, cooling, and bagging process in each production shift at regular intervals.

  • Maintaining a desired steam conditioning temperature of a minimum of 75°C(for poultry feed production) is not always possible and below this temperature, mold can’t be killed effectively.
  • Uneven cooling of feed at the cooler output leads to uneven feed temperature during bagging.
  • Moisture migration within feed bags due to warm feed packing also leads to mold infestation.

b. Moisture and water activity
It is essential to monitor both moisture and water activity as mold growth depends on water activity level which is an indicator of free moisture content in the material available for mold to grow. Periodically monitor process moisture at the mixer, conditioner, cooler, and finished feed bags along with water activity of finished feed bag. Optimization of the cooling process is important by managing the following variables:

  • Hot pellet temperature, moisture, size, density, and dust level.
  • Monitoring Ambient air quality and managing air flow rate.
  • Retention time, feed bed depth, and its uniformity in cooler.

It is advisable to keep finished feed moisture below 12% along with water activity (aw) level below 0.65 for improved feed shelf life, especially during summer and monsoon.
c. Time
Conditioning and cooling time is other important factors to be considered during processing. Maintain it as per the SOP designed for the type of feed. Cooling time in the counter flow cooler depends on ambient air flow rate, air quality, hot pellet size, and density. It is important to note that high velocity of air may lead to inefficient drying out of the core of hot pellets. The core moisture may come out to the surface during feed storage in bags. It leads to condensation and subsequent mold growth. Refer to table 1 and figure1 for getting a reference on cooling time for pellet feed. It is advisable to optimize cooler performance based on the ambient air quality of a particular feed mill location.
d. Ambient Air Quality
Ambient air in the feed mill plays a vital role in the feed milling process. Generally, the cooling process depends upon ambient air quality i.e., air relative humidity and temperature. Besides this, the storage quality of raw material in warehouses and silos depends upon air quality flowing through the material. So, it is advisable to monitor air quality in the feed mill at different locations by installing a weather station. It is especially recommended to install near the cooler area, warehouse, and grain storage silo area. Also, maintain proper ventilation in the feed mill to reduce the temperature of ambient air.
e. Raw Material and Finished Feed Quality
It is recommended to procure raw material as per the acceptance limit of safe handling for that feed mill. monitor raw material microbiological quality during its storage and design usage pattern based on that. Also, monitor the microbiological quality of finished feed.
3. Feed Mill Cleaning and Maintenance
It is advisable to prepare and follow the SOP of feed mill cleaning at regular intervals based on the type of feed production. Thorough manual cleaning of all feed mill machines, storage bins, and conveying equipment followed by flushing with an approved chemical that can yield effective cleaning. Conduct swab tests of feasible equipment before and after cleaning to understand the effectiveness of the cleaning process. Chemical flushing may not be done each week but cleaning of all feasible machines like a grinder, mixer, conditioner, and cooler should be done on weekly basis. The major objective of this process is to prevent cross-contamination in feed material during processing.
4. Usage of Reprocessable Material
There are leftover materials lying in the feed mill that is used later in production. Delayed usage of these materials may contaminate fresh feed during processing. So, it is advisable to use them in small quantities in selected types of feed with the consent of the quality control team. Use it either after treating it with an antifungal agent or maintaining proper conditioning temperature.
5. Water Seepage from Floor
Water seepage from the floor can be a potential cause of mold growth, especially at the bucket elevator boot area in the basement.
6. Insect Pest and Rodent Control
Insect pest and rodent damage raw material and finished feed and aggravates mold growth during storage. It is recommended to have pest and rodent control management by qualified professionals at regular intervals. Fumigation might also be needed to protect grain from insect pests for long-term storage.
7. Usage of Antifungal Agent
Use approved and effective antifungal agent or feed additive for further protection of feed in the supply chain until end consumption. It is important to choose an antifungal agent that gives long-term protection until consumption. A synergistic blend of organic acids and surfactant is effective against mold inhibition for long-term storage of feed.
8. Transportation
Proper transportation of feed in and out of the feed mill is also an important factor. The material should be properly covered providing protection from rain and other unfavorable atmospheric conditions.
9. Periodic Monitoring and Audit
There is a famous quote by Peter Drucker “You cannot manage what you cannot measure”. It is very important to monitor and measure all these above-mentioned factors at regular intervals based on need. Also, an audit from an external professional is recommended for a neutral view of the implemented process as per SOP and to bring continuous improvement.
It is evident that mold growth reduces nutrient availability in feed and is responsible for the potential development of hazardous mycotoxin. Its infestation can be controlled by developing proper SOP and managing it at each level of the feed production process in the feed mill starting from procurement of raw material to delivery of finished feed.

by Manab Samanta, Kemin Industries South Asia