It has long been desired to impart pleasant flavors and/or odors to various substrates particularly, as flavorings in food and fragrances in perfumes.  Over the years, particular fragrances and/or flavors have been identified with certain chemical compounds.  It is known, for example, that various gamma-lactones possess desirable odor/flavor characteristics.  As reported in Fernaroli's Handbook of Flavor Ingredients, Volume II, 2.sup.nd edition, CRC Press, 1975, gamma-hexalactone is known to possess the flavor-fragrance characteristics of coumarin or carmel.  Gamma-heptalactone is known to have a caramel or nutty odor and flavor, while gamma-octalactone is known to exhibit the flavor-fragrance of coconut or tonka.  Gamma-nonalactone has a cream, coconut or fruity odor/flavor characteristic, while gamma-decalactone's flavor-fragrance is creamy peach or apricot.  A peach or apricot odor/flavor is also exhibited by gamma-undecalactone, while a buttery or peach odor/flavor is exhibited by gamma-dodecalactone. 
In addition to the above-mentioned lactones, various alcohols and many other compounds are known to exhibit identifiable odor/flavors.  For example, phenyl ethanol is known to exhibit a rose/peach flavor-fragrance while benzyl alcohol is known to exhibit a fruity odor/flavor. 
Although each of the above-mentioned compounds are known to be flavor-fragrance additives, their manufacture to date has normally been effected by artificial means.  More recently, however, artifical flavor and/or fragrance additives have become increasingly suspect and are now generally less preferred over those food additives which are naturally derived.  Additionally, depending upon the particular artificial or synthetic process utilized in manufacturing particular flavorants, various artificial contaminants may be contained in the final product, which contaminants may exhibit undesirable side effects which would dictate against their routine used in flavor-fragrance materials. 
It has also been observed that one or more species of yeast or bacteria, when cultured under certain specific conditions, exhibit odors.  For example, lactones have been reported as metabolites of various microorganisms, such as the soil fungus Trichoderma viride which is known to produce a delta-lactone, 6-pentyl-2-pyrone, as its major odorant.  See Collins, R. P., 1976, "Terpenes and Odoriferous Materials from Microorganisms", Lloydia 39: 20.  Another organism, Ceratocystis moniliformis, generates gamma-decalactone when glycerol is used as a major substrate.  See Lanza, E., K. H. Ko, and J. K. Palmer, 1976, "Aroma Production by Cultures of Ceratocystis moniliformis", Journal of Agriculture Food Chem.  24: 1247.  Microorganisms are also known which can reduce gamma-keto-acids to gamma-hydroxy-acids which then cyclize to gamma-lactones.  See Muys, G. T., B. van der Ven, and A. P. de Jonge, 1962, "Synthesis of Optically Active Gamma and Delta-Lactones by Microbiological Reduction", Nature 194: 995.  As mentioned in the Collins article referred to above, phenyl ethanol and pentanol have also been reported as being formed by various microorganisms. 
Of course, many bacterial and/or yeast species are known to exist which do not produce any substantial volatile by products, much less any gamma-lactones.  The genus Pityrosporum is known to comprise four species, P. ovale, P. orbiculare, P. canis, and P. pachydermatis.  See Lodder, J., 1971, "The Yeasts", North-Holland Publishing Co., Amsterdam.  P. ovale and P. orbiculare are known to occur in areas rich in sebaceous glands, such as the scalp, face and trunk, P. ovale, being the most numerous organism on the scalp.  See McGinley, K. J., J. J. Leyden, R. R. Marples, and A. M. Kligman, 1975, "Quantitative Microbiology of the Scalp in Non-Dandruff, and Seborrheic Dermatitis", Journal of Investigative Dermatology, 64: 401.  Despite being ubiquitous, members of this genus are ill-defined, and morphologic characteristics serve as the prime method of identification (see the Lodder article referred to above). 
Occasionally, mostly in anecdotal references in the scientific literature, various types of bacteria and/or yeast cultures are described as emitting perceptible odors.  In one such instance, a culture containing P. ovale with Sabouraud's agar overlayed with olive oil was described as emitting a "distinctive, fruity, odor" Van Abbe, N.J., (1964), "The Investigation of Dandruff", Journal of the Society of Cosmetic Chemists, Vol.  XV, p. 609.  Of course, without identifying the particular chemical constituent(s) which might cause such odor and/or without further identifying whether and which of the experimental conditions may have led to the perception of such odor, such anecdotal references are of little use to the flavor-fragrance industry in its quest for new and improved flavor-fragrance additives.