Yeast is the invisible stuff that converts sweet wort into beer. For centuries it was considered part of a magical, or even holy, transformation that made fermented beverages a safe option to potentially dangerous supplies of water.  Fermentation was understood as a spontaneous process.With the advent of the microscope and the early microbiological studies of beer and wine by Pasteur and others, people slowly began to understand the function of yeast in fermentation. Some of my work with microbiologists has given me the opportunity to look at a number of different types of things in the scanning electron microscope. It differs from other kinds of microscope, by using a beam of electrons in a vacuum chamber to create a black and white photographs (there are no color electrons) that have high magnifications and great depth of field.

The light microscope is limited by the wavelength of visible light so the typical maximum magnification one can reach is about 1000x. Using an SEM, you can reach magnifications much higher than this, and the photos have a three dimensional quality that makes it look like you could reach out and pick up a single cell. Since the microscope uses a high vacuum and, I have to prepare the samples by dehydrating them. Because the electron beam is essentially a high voltage current, I also coat them with a bit of metal to improve their electrical conductivity. Yeast are single celled organisms that fall into a group called eukaryotes. They have relatively large cells that contain a nucleus and membrane bound organelles (this makes them more similar to homebrewers than bacteria). Yeast reproduces by budding (you can see numerous buds in the top photo) and each bud produces a new yeast cell. One of these yeast cells is about 5 microns long. That means that it would take about 200 of these end to end to stretch across a distance of one millimeter (1000 microns).

~ Karl Hagglund