Lab 4: Bread-making with yeast
In this lesson we watch the life of yeast. Equipment: slide and cover glass, pipette, microscope, filter paper, sugar, salt, warm water, flour, baker’s yeast. First yeast is added to warm sugary water and left in a warm place; soon the liquid froths and bubbles appear – a sign that the yeast cells are using the sugar and releasing carbon dioxide gas. A drop of the frothy liquid is placed on a slide with a pipette, covered with a cover glass, the excess is soaked up with filter paper, and it is viewed under the microscope: oval one-celled organisms, some with small buds. Then, with adults, dough is made: a pinch of salt and the frothy yeast are added to warm water, and a soft dough is kneaded with flour. The dough is covered and kept warm, and it rises and grows in volume because gas bubbles lift it. The risen dough is divided into pieces, left to rise a little more and baked by an adult in the oven. The soft, airy texture of baked bread comes from those bubbles.
Look at yeast cells under the microscope with the teacher and draw 3–4 of them. At home, with a parent, make dough, split it into two containers, keep one warm and one cold, and compare their volume after 1 hour. Record the result in a table. Safety: only adults work with the oven and hot dishes; do not eat raw dough; eat the finished bread once cool; wipe up spilled flour and water at once; wash your hands with soap.