Research now documents what producers and processors have always suspected: high somatic cell counts affect the shelf life of fluid milk. A Cornell University study, published in the February 2000 Journal of Dairy Science, shows that fluid milk containing a high level of somatic cells does have a negative effect on the taste of fluid milk 21 days after processing.

The study collected, processed and evaluated the quality of milk from eight cows before and after the cows were infected with Streptococcus agalactiae. The cows had an average somatic cell count of 45,000 cells per milliliter prior to the treatment, and an average SCC of 849,000 cells per milliliter after the treatment.

The bacteria and coliform counts for both the high- and low-SCC milk remained low throughout the trial. However, in the high-SCC milk, there was more protein and fat breakdown compared to the low-SCC raw milk. This breakdown of protein and fat led to quality problems.

Analysis of the milk’s aroma, taste and aftertaste was conducted on days one, seven, 14 and 21 after the milk was processed. (The milk was stored at 41 F between testings.) “Defects” were found in the high-SCC milk 21 days after processing. The analysis revealed rancid, oxidized and fruity aroma; salty, rancid, bitter and harsh taste; and bitter and lingering aftertaste. These defects led to a significant decline in the overall quality rating (OQR) for the high-SCC milk at day 21. The low-SCC milk had an OQR rating of 7.4, while the high-SCC milk had a rating of 5.15.

The researchers note that the exact time the milk began to lose quality was not determined — it could have happened anywhere between days 15 and 21 post-processing.