The reproduction of yeast can be divided into asexual reproduction and sexual reproduction.
Asexual reproduction includes budding, schizogenesis, and asexual spore production, while sexual reproduction mainly produces spores. Beer yeast undergoes asexual reproduction, mainly through budding. Its reproduction process consists of the following five stages:
- The haploid vegetative cells propagate through budding.
- The two vegetative cells combine to form a diploid through nuclear mating.
- Diploid cells do not immediately undergo nuclear division, but instead undergo budding propagation and become diploid vegetative cells.
- The diploid vegetative cells transform into ascospores, and the nucleus undergoes meiosis to produce four ascospores.
- The haploid ascospores serve as vegetative cells for budding.
The growth of yeast can be divided into five stages.
- Delay period: When newly inoculated yeast is introduced to a new environment, there is a stage in which the cell count does not increase. This stage is called the delay period. During this stage, some active substances in the cell have not reached the minimum concentration required for cell division, resulting in a “quiescent phase” before the logarithmic phase. The duration of the delay period depends on the condition of the microorganism itself and the nature of the medium.
- Logarithmic growth period: After the delay period, the yeast adapts to the new environment and enters the logarithmic growth phase characterized by rapid propagation. During this stage, the cells grow at the fastest rate, and the cell count increases almost linearly.
- Deceleration period: As cells continue to grow and reproduce, various factors such as substrate shortage, accumulation of harmful products, limited oxygen supply, or insufficient growth space may cause a slowdown in cell reproduction, leading to the deceleration period.
- Stable period: After the deceleration period, cell growth gradually slows down, and the growth curve becomes stable, entering the fourth stage known as the stable stage. The total number of living cells remains relatively constant during this phase, either because the number of new cells produced by division equals the number of dead cells or because the cells cease dividing while maintaining metabolic activity.
- Death period: With the depletion of nutrients and the accumulation of harmful substances, the environmental conditions deteriorate, resulting in a continuous decline in the number of living cells and the transition of cell growth into the death period.