Final answer:
Fresh yeast should be pure, effective in leavening, and free of contaminants, with a fresh smell, a creamy color, and a soft texture to be used effectively in bread rising and fermentation processes.
Step-by-step explanation:
Quality criteria for fresh yeast are crucial in both scientific experimentation and the culinary arts, such as bread and beer making. Fresh yeast's usefulness stems from its resilience and ability to remain viable under various conditions, including cooling, freezing, and drying. Its role in the fermentation process is to generate carbon dioxide, which leavens dough and contributes to the aerated texture of bread. However, not all yeasts are ideal for bread making. The desired qualities in fresh yeast include a high degree of purity, consistent leavening ability, and the absence of any contamination by bacteria or other undesirable organisms. It should have a pleasant, fresh smell, a uniform creamy color, and a soft, crumbly texture. Proper storage conditions are also essential to maintain yeast's effectiveness for bread rising and fermentation.