by Courtney Llewellyn
Associate Director of the Milk Quality Improvement Program at Cornell University Dr. Nicole Martin started her recent eOrganic webinar with a simple premise: The raw milk gathered on a dairy farm – and what is or isn’t in it – can greatly impact pasteurized dairy product quality.
“What happens on the farm does not stay on the farm,” Martin stated. If something is off with the milk from the cows, pasteurization is not a “magic bullet” that can fix it. High quality raw milk is the key to manufacturing high quality dairy products, from fluid milk to cheese to butter and yogurt. Raw milk factors that can affect finished product quality include somatic cell counts, total bacteria levels and total spore levels.
Somatic Cell Count
Martin noted that SCC is one of the most well-recognized raw milk parameters, and that a lot of producers do a great job monitoring and treating their cows to keep this number as low as possible. Variation in levels of SCs is tied to inflammatory reactions, stage of lactation, parity and hygienic factors. Martin said an average healthy, non-infected quarter SCC is 70,000 cells/mL. Infection is indicated at 200,000 to 250,000 SCC.
When farmers see an increased in SCC, they’ll also see reduced yield. Not only will there be less milk, the composition of it will change; there will be less casein, lactose and calcium and increases in albumin, sodium, chloride and enzymes. One enzyme Martin is particularly interested in is plasmin, which is heat stable and breaks down proteins.
High SCC in cheese products is especially problematic for a number of reasons. It leads to an increase in clotting time, increased moisture, reduced yield due to enzyme activity, reduced cheese fat levels and flavor and body defect development.
Factors that impact SCC in raw milk include the type of mastitis pathogen, the season, milking practices and hygiene (teat-cleaning and glove-wearing), milking equipment factors (flow rate) and housing area cleanliness. Monitoring these and using best management practices for cow health and cleanliness can definitely help improve SCC.
Total Bacteria Count
Also known as standard plate count (SPC) or total viable count (TVC), TBC has a top limit of 100,000 cfu/mL for individual producers, but Martin said 10,000 cfu/mL is achievable by most farms. Different bacteria can thrive at different temperatures.
The most commonly seen bacteria are those that cause mastitis, environmental contaminants, thermoduric bacteria (those that can survive the high temperatures of pasteurization) and psychrophilic bacteria (those that can survive very low temperatures). Martin explained that high initial contamination, improper cooling or long holding times may lead to high levels of psychrophilic bacteria at processing time, even though levels were within the safe zone at the time of milking. Psychrophilic bacteria can reduce yield by 3% – 4% and create flavor, odor and body defects in processed goods.
Cow and environmental factors on the farm affect bacteria levels in raw milk, and the natural flora of cow is not likely to cause high bacteria counts. How raw milk is handled, however, can influence TBC. “Bacteria are living, growing cells,” Martin said. “Even if the total count is good at the production level, if that product is held for a long time or at the wrong temperatures, it can go to levels to cause issues. Producers need to understand that can happen and that no individual process in the dairy continuum is alone – they all impact and roll into each other.”
The key for safety here is checking bacteria levels both at the farm and again before processing the milk.
Total Spore Levels
A spore is a reproductive cell capable of developing into a new individual without fusion with another reproductive cell. Endospores are formed under stressful environmental conditions and allow bacteria to persist in environments that would otherwise kill them, such as high heat, drying, radiation and sanitation.
Martin said this is a count more producers should be paying attention to. Mesophilic (growing at moderate temperatures) and thermophilic (growing at high temperatures) spores limit export opportunities in dairy powders, which is a large part of the U.S.’s dairy export market. One especially to look out for is Bacillus licheniformis, which is the most common spore former found in raw milk.
To keep spore levels low, Martin said farmers should mostly be concerned about cow and environment factors: udder hygiene, milking practices (in one study, proper employee training for teat cleaning led to a 40% decrease in spore levels in the bulk tank) and silage spore levels. With milking practices, forestripping is crucial, as it physically removes spores from the teat canal prior to milking and provides good stimulation for milk flow.
Farm Factors That Influence End Products
In addition to SCC, TBC and spore levels, there are also farm-related flavor and odor defects that can affect finished product quality. Martin said off odors and flavors may originate from the farm environment, whether they’re absorbed, bacterial or chemical. “Common defects include barny, cowy, feed/weed, malty and oxidized odors or tastes,” she said. And if there’s a sensory defect in the raw milk, it will likely carry over into finished products.
Martin recommended screening raw milk for flavor and odor defects periodically as part of your overall milk testing program, either annually, quarterly, monthly or more frequently, depending on your needs. Producers also need to focus on attributes that originate at the farm.
“Cow, farm and processing facility factors affect raw milk parameters and should be optimized to ensure high quality finished products,” she concluded.
For more information on these topics, Martin will be leading a free two-part virtual workshop on the impact of organic raw milk quality on pasteurized dairy product quality – the two-hour, self-paced “Raw Milk Quality 101” and a five-hour live session, “Farm Management for Producing High Quality Raw Milk,” on Dec. 16. Registration will open soon through eOrganic.
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