The relation between moisture content and moulding in cured hay.
Samples of cured hay have been stored in closed containers at relative humidities of 0–95% at temperatures varying from 5 to 25° C. A curve relating equilibrium moisture content to relative humidity of the store has been constructed and the incidence of first mould growth noted. An explanation has been suggested to account for the apparent discrepancy between earlier published work concerning the onset of moulding and conditions normally prevailing on the farm. In laboratory storage experiments temperature conditions are relatively constant, whereas with hay stacked in the open air the high atmospheric humidity in winter is offset by a lowered temperature, and the higher summer temperature is accompanied by a lower moisture content in the hay.
Role of Water Activity in the Spoilage of Alfalfa Hay
Abstract Moisture sorption isotherms of alfalfa stems and leaves obtained from the first and third cutting of the season were constructed. Important differences in the relationship between moisture content and water activity values for alfalfa stems and leaves were observed. The extent of those differences was influenced by the initial moisture content and maturity of the alfalfa plant. Water activity, not moisture content, determined the nature of fungal growth on alfalfa stems and leaves. At water activity of 1.0 (moisture content, 51.7 to 65.3%), fungal growth was characterized by extensive mycelial development. Reducing the water activity to .93 (moisture content, 28.1 to 41.7%) dramatically increased fungal fruiting body development and reduced mycelial development. Even though alfalfa stems are nutritionally inferior to alfalfa leaves, fungal fruiting bodies appeared sooner on the stems at water activity values less than .81. Addition of a rich nutrient source, yeast extract, to the stems and leaves did not change that relationship. Analysis of the experimental results reported showed that alfalfa stems have a greater spoilage potential than alfalfa leaves. Implications of these findings to the spoilage process and the nutritional quality of baled alfalfa hay are discussed.
STUDIES ON PENICILLIUM CHBYSOOENUM THOM, IN RELATION TO TEMPERATURE AND RELATIVE HUMIDITY OF THE AIR
SUMMARY. 
 
(i) Germination and viability of conidia of P. chrysogenum. 
 
 
 
1. Conidia were found to germinate in moist air on glass in atmospheres ranging in relative humidity from 100 to 81 per cent, and in temperature from 1 to above 35 but below 40° C, with the optimum temperature lying near 25° C. 
 
 
 
2. At constant temperature the latent period of germination generally shortened as the relative humidity of the air rose, and when liquid or gaseous water was replaced by 2 per cent, malt agar. 
 
 
 
3. The latent period of germination in water of conidia from old cultures (120 or 210 days old) tended to be longer than that of conidia from young cultures (3 days old). Variations in the intrinsic characters of the conidia caused irregularity in the results which was not shown when the conidia were germinated on 2 per cent, malt agar. 
 
 
 
4. Conidia were exposed for periods up to 136 days to atmospheres of temperatures 20 and 30° C. and of relative humidities 72–6, 26 and 0 per cent, (approx.). The percentage germinations in water and on agar within 24 hours, and in water, after submersion for periods up to 216 hours, were determined. No correlation was found between the length of exposure of conidia to various atmospheres and the ultimate germination in water, though during the first 24 hours of germination on agar and in water increased length of exposure generally resulted in decline in percentage germination. 
 
 
 
5. Exposure of conidia to atmospheres of 0–100 per cent. R.H. and 1–100° C. showed that conidia possess considerable powers of resistance to heat for temperatures up to 30° C. in atmospheres of relative humidity 0 and 26 per cent, and can live in the latter for more than 129 days; at temperatures above 40° C. the time required to kill the conidia at the same temperature falls with rise in relative humidity, and at the same relative humidity falls with rise in temperature.