Yeast Treatise - Dough Fermentation & Temperature

Dough Fermentation & Temperature

There is a specific relationship between yeast and temperatures. Like most living organisms, the metabolic activity of yeast ceases above and below certain fairly well defined temperatures. Its ability to leaven is also effected over a broad thermal range. These are summarized in Table 4 below.

Temperature	Activity

-20 C. (-4 F)	Loss of Fermentation Capacity
< 20 C (68 F > 40 C (104 F)	Growth Rate Significantly Reduced
20 C (68 F) - 27 C (81 F)	Most Favorable Range For Yeast to Multiply
26 C (79 F)	Optimum multiplication of Yeast Achieved
27 C (81 F) - 38 C (100 F)	Optimum Fermentation Range
35 C (95 F)	Optimum Fermentation Temperature
> 60 C (140 F)	Yeast cells Die

The temperature of the fermenting medium also exerts a significant effect on the yeast's gassing rate. As a general observation, the fermentation rate increases with a rise in temperature up to a maximum of perhaps 100 to 105 F (38 to 41 C). The rates of carbon dioxide generation of dough without added sugar over a 3-hr period at various temperatures within the range of 81.5 to 95°F (28 to 35°C) are shown in Graph 1. (Pyler)

Rapid assimilation by yeast of the free sugars available in the flour accounts for the initial rapid activity shown in the first minutes. The subsequent drop-off in the rate that follows marks the exhaustion of the supply of this free sugar, and the period of adaptation of the yeast to the fermentation of the maltose that is being produced by the action of amylases on the damaged starch in the flour. After this period, the gassing rate rises again for about 3 hr, or when the maltose supply is also depleted. Interestingly , the fermentation is faster at 35 C (95 F) and an earlier exhaustion of the maltose supply occurs. Thus the final decline in the carbon dioxide is most pronounced here rather than at the bit higher temperature of 90.5 C. (32.5 C).

Once the dough or ferment temperature exceeds about 105°F (41 C), the fermentation rate declines. Yeast enzymes are generally inhibited at this temperature. Table 5 below (derived from Pyler) correlates the effects gas production and temperature in liquid ferments. As can be seen, gas production increases as the temperature rises to 100 F (38 C). It then declines at higher temperatures. (Note: All temperatures are rounded)

Temperature

Deg. C Deg. F

Maximum Gas Production Rate: In Millimoles CO /hr/g/Dry Yeast Solids

Time to Maximum gas Production rate (in Min.)

29	84	20	150
31	88	23	135
33	91	24.5	135
36	96	25	120
38	100	26	90
40	104	22.5	75
42	108	20	30