Importance of project: A sweet hazelnut flavor, a pliant texture, and large, evenly distributed "eyes" characterize high quality Swiss of Emmenthaler cheese. The typical sweet flavor is chiefly due to bacteria which produce propionic acid, acetic acid, and carbon dioxide. The eyes are formed from the gas, mainly carbon dioxide, produced by these and other bacteria. Krett and Stine (20) have found that the lower fatty acid content of a Swiss cheese generally indicates its quality. A study of factors which may influence the amount and ratios of the volatile acids should be helpful in determining manufacturing and curing procedures which will give a fine flavored product. Purpose of investigation Commercially, Swiss cheese is usually made from raw or heat-treated milk. Experimentally, hydrogen peroxide treated milk has shown some promise. A comparison of these three milk treatments was made to determine the effect they have on the volatile fatty acid content and cheese quality. Some successful cheesemakers add no prepared cultures of propionic acid bacteria (Propionibacterium shermanii); some add small amounts, while others advocate larger inoculums. Cheese in this experiment was made with varying amounts of added Propionibacterium shermanii culture to study the relationship to the lower fatty acid content, eye formation, and quality. This experiment is a study of the butyric, propionic, and acetic acid content of 4-month old cheese as affected by the above mentioned milk treatments and Propionibacterium shermanii culture variations.