While touring the Tillamook Cheese Factory, I was looking over the display case, intrigued by the mix of ornate glassware and rugged mechanical tooling. The slender-necked bottles were calibrated. The tool had a clamp mount and a crank. “Wait a minute,” I thought, “That’s not for churning, that’s a centrifuge!”
US dairy standards in the late 1880’s were a lax affair. Very few dairies had the interest or capability to execute the tedious laboratory manipulations to determine the butterfat content of milk, the key determinant of milk quality. Dr. Stephen Babcock, a Professor of Agricultural Chemistry at the University of Wisconsin, was presented with the challenge of generating a “practical, workable test for butterfat, that could be applied by farmers or creamery operators working without a laboratory.” Starting from a more complex assay developed by his colleagues, he soon had an assay that worked, with one exception.
“Hundreds of tests were made by my first method, all of which were satisfactory except with the milk of one cow, ‘Sylvia’ in the station herd, a Jersey of good type and normal in every way.”
Stymied by Sylvia’s milk, it eventually led Dr. Babcock to the critical variable: sulfuric acid.
Milk is a colloidal suspension, a mixture of lipids, carbohydrates, protein and minerals. The stuff we call “butterfat” comes from the lipid suite, which is a mixture of various hydrophobic entities. The key lipids in butterfat are triacylglycerols and phospholipids. Triacylglycerols are a dense source of energy, but they’re not soluble in water, so they aggregate instead of disperse. Phospholipids are chemically similar to soap – long fatty chains with a water-soluble headpiece. Nature conspired to combine these into an aqueous fat delivery system. The phospholipids coordinate a water-friendly shell of proteins and carbohydrates around a rich payload of triacylglycerols. These vessels are referred to as “fat globules,” and a schematic is shown below:
These fat globules are dispersed throughout milk, protected by their membrane shell. If you want an accurate quantitation of butterfat, you have to break these shells apart. Dr. Babcock discovered that concentrated sulfuric acid was the best way to do this. Sulfuric acid rapidly degrades proteins, cleaves polysaccharides, and solubilizes the minerals. This assault on the hull of the fat globule boat allows the payload of triacylglycerols to pour into solution. Buoyant, repelled from water, they soon aggregate and float to the top of the solution. Just as important, sulfuric acid proved to be an ideal solvent for dissolving the non-lipid components of milk, resulting in a neat liquid partition between fat and non-fat. In a final, elegant twist, the chemically-derived heat generated in the process further increases the solubility of the aqueous components and enhances the density difference between the water and fat layers. Before this heat dissipates, a relatively modest application of gravity via a centrifuge quickens the separation and completes the assay.
Dr. Babcock’s assay was published in July of 1890 and had an immediate impact. A ready assay for butterfat content allowed for a standardization of milk blends. Illegal milk dilution became a relic of the past. Dairies could set prices based on the richness of the product, which provided farmers an incentive to improve butterfat production. Farmers could now readily assay their own product before sale, creating transparency throughout the distribution system. Stock breeders focused on balancing production quantity with butterfat quality. By 1899, Dr. Babcock was awarded a medal by the Wisconsin legislature. It was soon followed by recognitions from New Zealand and Australian dairy farmers, and grand prizes at the Paris (1900) and St. Louis (1904) expositions.
Remarkably, Dr. Babcock showed no interest in pursuing material gains for his discovery. The initial disclosure of the assay concluded with the words: “The test is not patented.”
Before his death in 1931, Dr. Babcock made numerous other discoveries at the forefront of nutritional science, including experiments which led to the discovery of vitamins.