Properties of Yeast in Food Processing Yeast is one of the important groups of microorganisms in food microbiology, because in addition to its properties that can cause Food spoilage yeasts are also widely used in producing foods. fermented foods. As a food spoilage organism, yeast often grows on foods that contain sugar and cause odor changes such as sour or alcoholic odor, causing turbidity, formation of mucus, films and growth on surfaces, deposits and so on. B. Materials and Tools Culture:        Baker's yeast (4 kinds of brands) Yeast tape (4 kinds of brands) Candida is useful Endomycopsis fibuliger Saccharomyces cerevisiae Saccharomyces cerevisiae var. elipsoideus Other yeast cultures Foodstuffs   Flour Rice Medium :  Per group: 4 tubes of sterile orange juice + Durham tube 4 tubes of Litmus milk 4 molasses tubes + durham tube 4 cups PDA agar Tool :       200-250 mL beaker Erlenmeyer tubes 100 mL and 200-250 mL 250 mL measuring cup greased with cooking oil Pipettes, test tubes, petri dishes Object glass, cover glass Microscope C. How it works Culture preparation Each group chose one brand of baker's yeast, one brand of tape yeast, and two kind of yeast culture. To activate bread yeast and tape yeast, 2 grams of yeast bread or yeast tape dissolved in 30 mL of warm water in an Erlenmeyer 100 tube mL, stir until dissolved and leave for 10 minutes. For tape yeast culture used is the upper liquid. Bread Yeast Activity Test A total of 25 grams of wheat flour was weighed and mixed with 25 mL Suspension of baker's yeast in a 200-250 mL beaker by adding flour little by little. Bread dough is made by pressing with a spoon or glass rod for 5 minutes. The dough is then put into a measuring cup 200-250 mL, the edges of which have been coated with cooking oil, and pressed onto the part bottom of the tube. The initial volume of the dough is recorded, then the dough is incubated at temperature room for 2 hours, and observe the increase in volume every half hour. Volume increase is expressed in mL per 30 minutes, and compared to activity the four tested bread yeasts. Tape Yeast Activity Test A total of 50 grams of rice was weighed and put into an Erlenmeyer tube 200250 mL, then sterilized. Add 50 mL of yeast tape suspension by dripping it evenly. Incubation was carried out at room temperature for 2 days, and observe the formation of liquid by pouring the liquid form into a glass and see the volume. Another observation is measurement of pH, total acid and the appearance of a sour/alcoholic odor. To measure total acid, 10 mL of liquid was pipetted and transferred into a 50 mL Erlenmeyer tube, mixed with 10 mL of distilled water and added 5 drops of 1% phenolphthalein indicator solution. Titration is carried out using NaOH solution 0.1 N until pink appears. Total acid was calculated as mL of 0.1 N NaOH required for centrifugation. Yeast growth A total of 0.1 mL of yeast culture and suspension of baker's yeast and tape yeast were pipetted and each is put into a tube containing orange juice, Litmus milk and molasses. Incubation was carried out for 2 days at room temperature. Observe the growth of the yeast in orange juice and molasses by observing the formation of turbidity, sediment, film on the surface, formation of gas and sour/alcoholic odor. Internal growth Litmus milk was observed as stated. Yeast morphology Yeast cultures and suspensions of baker's yeast and tape yeast were each etched on the PDA agar plate and over the scratch covered with a cover glass. Incubation was carried out at room temperature for 2 days, and formation was observed pseudomycelium on the growth around the cover glass using microscope with 100x and 400x magnification. From each yeast culture and suspensions of baker's yeast and tape yeast are made wet preparation and methylene blue staining on a glass slide. Watch below microscope with lowest to highest magnification for size and shape cells, as well as vegetative reproduction methods such as budding, division or fission shoots. How to color. Make a thin film of yeast culture on a glass slide. Let dry, then fix over the fire slowly. Drop the methylene blue solution for 2 minutes, then washed with running tap water until there is no color which fades. The remaining water is absorbed with filter paper and observed under a microscope from lowest to highest magnification.