Bacteriophages for lactic streptococci were found to occur in the atmosphere of commercial cheese factories. Finely divided particles of whey emitted from the whey separator appeared to be the main vehicle for the air-borne phage although whey-contaminated dust probably also played a part. The concentration of air-borne phage was sometimes so great that, with the use of a normal bacteriological aseptic technique, it was impossible to prevent infection of the starter cultures for more than a few propagations. Protection of the starter from air-borne phage eliminated phage failures.

The question of the origin of bacteriophage is discussed in the light of the recognition of the prevalence of air-borne phage. The occurrence of air-borne infection could account for most of the instances of starter failures which were previously thought to be due to spontaneous phage development within cultures.

1. Experiments have been carried out in order to determine the best method of neutralizing cheese whey prior to drying by the roller process. The use of sodium or potassium compounds leads to difficulties in drying and the production of an unpalatable product of poor quality. Neutralization with calcium hydroxide gives a satisfactory product. Over-neutralization must be avoided.

2. Complete neutralization of hydrochloric acid casein whey results in the formation of a flocculent precipitate and deterioration in the drying properties; reduction of the acidity from 0·48 to 0·18% by the addition of calcium hydroxide allows successful drying and yields a reasonably satisfactory product. The latter is, however, definitely unpalatable.

3. Acetic acid casein whey can be dried without any previous neutralization to yield an excellent and palatable product.

Experiments were carried out to study the effects on the quality and nutritive value of bread of the addition to white flour of roller-dried skim milk and roller-dried whey. Both samples were typical commercial products.

Additions of 2% of the dried milk could be made without any marked effect on loaf quality or on flavour. The addition of 4% or more definitely lowered the quality of the bread, the volume being smaller and the crumb more rubbery. As the content of milk was increased above 2% the flavour of the bread became increasingly distinctive and departed from the normal neutral flavour of water bread.

Up to 5% of dried whey could be added to the flour without any marked deterioration in the crumb of the bread, although with one flour this quantity decreased the volume by 16%. At this level, however, the whey imparted a distinct cheesy flavour to the bread.

Attention is drawn to the fact that the effects produced by the addition of dried milk or whey to bread can only be considered in relation to the particular sample used, since other workers have found that modifications in the method of manufacture considerably alter the value of the product as far as its use in bread is concerned. For this reason improved types of dried milk or whey might well lead to their greater use by the baking industry.