Convective drying of baker’s yeast pellets containing a carrier

Abstract

The drying behavior of yeast pellets containing a carrier was investigated. Yeast paste was mixed with different amounts of wheat flour, a solid carrier, to obtain spherical pellets with 69, 55, and 40 wt% of water. During the drying, the pellets moisture content, surface temperature, and dimensions were measured, using a balance, an infrared camera, and a stereomicroscope, respectively. A drying kinetics model was developed and successfully challenged to the experimental results. The experimental and modeling results give insights into the phenomena taking place during the drying of yeast pellets including a carrier. These results highlight that the addition of a carrier reduces the shrinkage of the pellets and increases the drying rate. Moreover, the results seem to indicate that an osmosis process may take place inside the pellets following the addition of the carrier.

Evolution of the quality of baker’s yeast pellets containing a carrier during their convective drying

“…[3,[23][24][25][26][27][28] For example, Liu et al [26] observed that yeasts dried with wheat bran have a better activity than those dried with rape seeds. In our previous work, we have shown that the addition of wheat flour reduces the shrinkage of the yeast pellets during their drying [22] but, on the other hand, the observed increase in the dehydration rate caused by the carrier might have a detrimental effect on the quality of the yeasts, as mentioned in several studies. [4,7,18] Numerous parameters can influence the quality of microorganisms during their drying, which may explain differences between studies and make comparisons difficult.…”

“…The moisture content of the yeast paste is around 69 wt% on a wet basis while the wheat flour used as a solid carrier contains around 10 wt% of water. As previously explained in our previous work, [22] the fresh yeast and the wheat flour were mixed in different concentrations and the mixture was extruded into spherical pellets of 3 mm in diameter. Three sample groups were compared: yeast pellets with no carrier (hence with 69 wt% of water), yeast pellets with carrier and with approximately 55 wt% of water and yeast pellets with carrier and with approximately 40 wt% of water (see Table 1).…”

“…The experimental setup is presented in more details in other papers. [4,22] Partial drying experiments were stopped before the end of the drying, at different moisture contents, to obtain samples for which the fermentation activity of yeasts was measured. Drying experiments were also conducted until the weight of the yeast pellets reached a constant value.…”

“…In one of our previous work, the drying kinetics of yeast pellets containing a solid carrier, wheat flour, was investigated. [22] Wheat flour was used as a carrier because it is a hygroscopic material safe for consumption. We have shown that the addition of this solid carrier increases the drying rate of the yeast pellets.…”

“…Therefore, the main objective of this short communication is to complete our previous study on the drying kinetics of yeast pellets containing a solid carrier by analyzing the influence of the wheat flour on the quality of the yeasts. The fermentation activity of the yeasts with and without carrier in the pellets is measured throughout the drying process, in order to evaluate the impact, for the conditions tested in our previous work, [22] of the addition of wheat flour on the quality of the yeasts.…”