The production and distribution of milk and fluid dairy products have changed dramatically during the past 25 years. Some of the more significant developments relate to the decline in the number of small dairy farms and processing plants and the emergence of the large commercial "Super Farms" and highly automated "Super" processing plants with wide distribution areas. These developments, coupled with the widespread trend toward warehouse distribution to stores vs. direct store delivery (DSD) have created a need for increasing the shelf-life of dairy products. Shelf-life extension is a popular topic of discussion at almost all industry conferences and meetings.
Ultra High Temperatures (UHT) and Extended Shelf-Life (ESL) processing and packaging systems are proven methods of extending shelf-life. These processes have gained acceptance for selected low-volume items, but have not been widely utilized for the high-volume fluid milk products. Unfortunately, there are no magic solutions for extending the shelf-life of products processed and packaged using conventional equipment.
Shelf-life can be maximized by strict adherence to the basics in three essential areas of production and distribution. Let's take a brief look at each area:
Raw Milk Quality
Quality starts at the farm and must be maintained through delivery and storage prior to processing. There are three cardinal principles to achieving quality standards:- Keep it CLEAN-Effective sanitation practices.
- Keep it COLD-Cool quickly and keep temperature below 40° F. Life begins at 40° F for spoilage bacteria.
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Keep it FRESH-Milk does not age well. Control inventory and keep it moving.
High quality raw milk will have low microbiological counts. Two suggested standards for key quality indicators are:
- Direct Microscopic Count (DMC): < 50,000 clumps / mL
- Preliminary Incubation Count (PI): < 50,000 cfu / mL
Sanitation
Effective sanitation must be achieved in order to prevent or minimize post-pasteurization contamination with spoilage organisms. There are two broad groups of psychrotrophic bacteria that must be controlled. The first are the Gram-negative rods such as Pseudomonas and their close relatives. These bacteria are the "traditional" spoilers of dairy products. They grow well in refrigerated products and are almost always caused by post-pasteurization contamination. The second group of psychrotrophic spoilers are Gram-positive bacteria, most commonly spore forming rods of the genus Bacillus. The Bacillus bacteria grow at a much slower rate than the Gram-negative bacteria and become an issue when shelf-life is extended beyond 14 days at 45° F.Traditional microbiological testing procedures are not adequate for evaluating the effectiveness of the sanitation process when extended shelf-life is the goal. Stress testing procedures (a topic for a future article) must be utilized.
Refrigeration
This is the most practical insurance available for extending shelf-life. The colder milk is kept, the longer it will last. Life begins at 40-that's 40ºF for spoilage bacteria. Thumb Rules:• Each 1° F increase in temperature above 40° F will reduce shelf-life by one day.
• Each 5° F increase in temperature will reduce shelf-life in half.
• Milk in a warm room will increase in temperature 8 - 10 times faster than it will cool down when placed back in refrigerated storage.
KEEP IT COLD. The psychrotrophic spoilage bacteria are capable of growing at temperatures of 32 - 45° F, but their optimum growth temperatures are 77 - 86° F. Their rate
of growth increases as temperature approaches the
optimum range.
