Yeast, the Basics & Background

This is a portion of an image of Dry Lager yeast placed in a micro titer plate, with 20% malt extract. The cells are at 10X magnification and are about 5 microns in diameter. and after 10 hours… Yeast is a single cell fungi used in many different fields, from cooking to cellular research to beer and wine making. Since I make beer and we generally look at cells under a microscope here at Kairos Instruments, it seemed like a good area for some further study. Turns out there are a lot of different types of fungi – 1.5 million species, and there are 1,500 species of yeast alone. Fungi are a different classification from plants, animals and bacteria. The main difference is the cell wall contains chitin whereas cell walls of plants contain cellulose, and animals actually lack a rigid cell wall. Chitin is a long chain polymer, a derivative of glucose. This polymer is also the exoskeleton of many crustaceans like crabs and shrimp. Yeast is a small cell, 3 to 7 microns in diameter, 7 microns = .00027 inches. Some yeast cells reach 40 microns in diameter, .0016 inches. Many of these cells derive their energy from fermentation, a chemical conversion of carbohydrates to ethanol and carbon dioxide. The process of using yeast as an industrial organism, that is to produce alcohol, is over 4,000 years old. Yeast was first observed under a microscope by Anthony van Leevwenhoek (1632-1723), “layu-wen-hook”.  Anthony was the first to see blood … Continue reading

Yeast Experimentation

In dealing with a cell like yeast, it occurs to me that there are a lot of questions in my mind about what causes yeast to grow. All cells need the proper environment to grow. They need food, the correct temperature and the right fluid / gas exchange. Given the proper environment, cells will divide, consuming nutrients and producing a preferred product. For yeast, the product would be CO2 for baking, or alcohol in beer making. Different types of yeast you would assume would need different food and may change characteristics based on the environment. We know in our work at Kairos Instruments, that hematopoietic stem cells for example are said to need a niche, a special place, to grow and divide to produce cells for our blood system. In the case of yeast, an environment without oxygen allows the cell to consume sugar and produce alcohol, but in the presence of oxygen, no or little alcohol is produced. So, environmental conditions effect the outcome of cell division. A question to be answered then is what nutrients and how much are needed to establish good growth. A second issue is the temperature. Most lager yeasts need a colder temperature to work properly and most ales work best around room temperature. Changes in temperature affect the yeast efficiency and in many cases the flavor component will also be affected. The next issue in my mind is the amount of yeast present in the experiment. In many cell types, if the starter … Continue reading

What Plate to Use

To run just about any experiment on the microscope, you have to put cells in a dish, on a slide or in a microplate. Most of our experiments are run in a microplate, so I will concentrate on these style plates. Microtiter plate it turns out is a registered trademark of Cook Engineering Company, so I will use the generic term microplate (1). Depending on the experiment, there is a wide variety of microplates. The more common plates are 6, 12, 24, 48, 96 and 384 well plates. There are plates with yet higher numbers of wells: 1536, 3456 and 9600, these plates are very difficult to manually pipette into, designed for automation. There are different styles of plates as well, round and square as well as different volumes and different coatings. As with anything, it’s important to pick the best plate for the experiment and to be aware of some issues involved with plates. Since we do visible imaging and try to have multiple variations in each experiment, we shoot for smaller volume higher density plates. For example, if the experiment involves the effect of extract concentration on yeast cell growth, you will need a number of wells to look at the effect. Let’s say you want to look at 5 different concentrations of extract, then a negative control and a positive control, that’s 7 wells for one concentration of yeast. Next I may want to see if there is an affect with yeast concentration as well, so maybe … Continue reading

How Do I Analyze My Experiment?

In a typical live cell experiment, many locations are taken in a specific well and many wells are included in the experiment. The first important thing to consider is how many images should I take in a given well, then how many replicates should I have to make sure I am seeing a given effect. That will be covered in a future write up on statistics. But in any case, a typical experiment will last many days with each location producing a series of images, typically every 10 to 15 minutes between images. The first way to look at the results of an experiment is to just look at time lapse images using any image viewer. That will give you a sense of the experiment – did the cells grow, do they look healthy, do you see any general trend. The next step is to produce an AVI of some interesting events in the experiment. For this process we recommend an open source package, ImageJ. ImageJ will run on most computers, it’s been around since 1997 and has many simple and advanced image processing operations. To load a sequence of images in ImageJ, just select File>Import>Image Sequence…, then locate the starting image for the sequence. The program will load all the images. You can view the image sequence and can also save an AVI of the sequence, select Save As>AVI. You can now send this AVI to anyone or store the sequence as a single file. ImageJ will also load … Continue reading