We are having our HS freshmen bio students design and execute an experiment
centered around yeast fermentation. Essentially, they will mix yeast cultures and different
substrates (sugars) together in an inverted pipette and measure the rate of activity by the amount of CO2 generated per unit time. Variables which they might examine include temp,
yeast concentration, substrate conc, types of yeast and types of substrates.
 
I'm having a bit of difficulty in finding some logistic information in the
literature. Some questions I have include:
 
1. Getting the yeast up and running so that they are active enough for students to get "good" readings in a 1-hour lab. Readings will take place in an inverted 1 ml plastic pipette. Some places indicate that 5 minutes in "warm" (temp?) water is enough to get them going; others suggest a few hours fermentation in a warm sugar solution is necessary.
 
2. How long do the yeast remain active (viable?)
 
3. Suggested brands, types of yeast (a variable in our expt.)? Is "rapid rise" type yeast preferable over other types?
 
3. Concentrations of sugar solutions. I suspect that hypertonic sugar solns. (e.g., honey) might
be more detrimental due to their osmotic effects. I've seen 20% sucrose as a suggested "base" a few times...
 
Any advice at all would be greatly appreciated. We are using a modified approach to that published in Carolyn Eberhardt's "General Biology Labs for Saunders Biology" lab manual. Thanks so much in advance.
 
"Science is built of facts the way a house is built of bricks;
but an accumulation of facts is no more science than a
pile of bricks is a house."
- Henri Poincare
 
Todd Bennethum, Science Teacher
Arapahoe High School
2201 E. Dry Creek Road
Littleton, CO 80122
 
e-mail: tbenneth@model.cudenver.edu
WWW: http://bilbo.bio.purdue.edu/~tbenneth
 
(303) 347-6000 School
(303) 347-6090 FAX
(303) 683-6983 Home
 
 
In our Intro Lab we have students compare fermentation rate of solutions in
room temp vs warm water baths. In a flask we put 400 ml apple juice, 50 ml
sugar, and 1 package Fleischman/s yeast (not rapid rise). It takes about
45-60 min to get going, and it typically lasts about 30 min or so.
 
***************************************************
Ed Alkaslassy (503) 359-2967
Dept. of Biology FAX: 503-359-2933
Pacific University <alkaslae@pacificu.edu>
Forest Grove OR 97116
 
 
Hello LABBERS! Dear TODD, I LOVE Saccharomyces cerevesiae! It's
cheap and "works" every time. HOWEVER, the key to yeast is temperature! As
any baker (or brewer) knows, yeast needs about 105 F. We use yeast for our
TechPrep integrated studies "bridge" course, introductory college biology
(nonmajor) and botany classes. Candace Brenner, our Instructional
Associate, invented a great yeast "holder" using a small "cheap" plastic
storage container (similar to Tupperware, rubbermaid, etc.) with watertight
lid, that holds two test tubes. Next she used one plastic stopper with
plastic tubing to connect the "yeast growth chamber" to collect evolving
gas. DON"T USE GLASS tubing--it BREAKS! DON"T use rubber tubing, it rots
with air pollution. Fill the plastic container with warm water, keep the
yeast in a warm location during the lab. You can collect the gas with one
of the test tubes inverted (first fill with warm water). The other tube
holds your yeast solution and is connected to stopper-tubing. Evolving gas
displaces the water. I use a phenol red solution as an indicator to
determine whether the gas evolved is air. We connect one plastic tube to
our "air jets" (an aquarium pump would work fine) and bubble "air" through
phenol red. I eliminated lime water ages ago as a CO2 indicator. When the
CO2 bubbles through the phenol red, it dramatically turns bright YELLOW (due
to carbonic acid). This phenomenon leads to discussions about orthodontic
braces, acid, soda pop, ad infinitum.
 
What a wonderful investigative applications study. Have the
students test different amounts of yeast, temperatures, sugars, concns.
etc., etc., for growing the stuff. As a result of this lab, one of my
(over 21 yrs.) students made a videotape explaining how to make beer. That
sure gets students' attention. No copyright problems, either! For the
nonalchol-oriented individuals, pizza dough also helps them connect with how
yeast works. Sometimes I bring in my Wellbuilt "R2-D2" automatic
breadbaking machine, start the bread early in the morning, and have hot
bread during the labs. Talk about multisensory learning experiences! YUM!
 
"Regular" or non-rapid rise yeast begins to "work" very
quickly--not 50-60 min. Don't stir--float the yeast on top of your liquid.
 
Bon Appetite! ENJOY. Sharron Clark, Golden West College, CA
 
 
Todd, my experience with yeast is mostly with bread baking. We use two
cups of warm water, about a tablespoon of table sugar and about two
teaspoons of Red Star yeast that we buy by the pound at Sam's Club.
Within 5 minutes there's lots of activity.
 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Jean DeSaix, Ph.D.
Department of Biology Coker Hall CB#3280
University of North Carolina at Chapel Hill, NC 27599-3280
Work Phone: 919-962-1068 Home Phone 919-929-1580
FAX 919-962-1625 email jdesaix@email.unc.edu
 
 
Todd,
 
Here at Smith we do a similar exercise as you have described below
except that we use a pressure transducer to measure the amount of
CO2 that the yeast evolve (see abstract from ABLE meeting 1994).
 
I wish I could point you to one neat source of "All you ever wanted
to know about yeast...", but I have never seen one. Perhaps the
Fleischmanns Co. could help. However, I do have info. on the
fermentation rates of various mono- and disaccharides and the
mechanism used to transport then across membranes. I'll send my notes
on this to you by snail mail.
 
We have also gathered a lot of info as a result of student
experiments (but they are not always reproducible!!). I'll
try to answer your questions below.
>>
>> 1. Getting the yeast up and running so that they are active enough for
>> students to get "good" readings
>> in a 1-hour lab. Readings will take place in an inverted 1 ml plastic
>> pipette. Some places indicate
>> that 5 minutes in "warm" (temp?) water is enough to get them going; others
>> suggest a few hours
 
Temp. is crucial for getting yeast active, the warmer the better, but
this introduces another variable. ( We raise the room temp. to 25C
the week we do this experiment.) I start the yeast about half an
hour before the lab in distilled water. It doesn't bubble much since
the temp. is less than optimum.
 
>> fermentation in a warm sugar solution is necessary.
>>
No, but if you have a small amt. of sucrose this will get it
bubbling.
 
>> 2. How long do the yeast remain active (viable?)
>>
Not tried to find this out, but over a 3 hour lab the yeast seems to
be fine... although I have seen weird behavior where the activity
seems to dramatically improve after an hour.
 
>> 3. Suggested brands, types of yeast (a variable in our expt.)? Is "rapid
>> rise" type yeast preferable over other types?
>>
There seems to be small diff. in the different brands, but this is
probably experimental error. We have tried cheap -> expensive
brands; however, the rapid rise does become activated more quickly.
 
>> 3. Concentrations of sugar solutions. I suspect that hypertonic sugar
>> solns. (e.g., honey) might
>> be more detrimental due to their osmotic effects. I've seen 20% sucrose as
>> a suggested "base" a few times...
>>
Conc. over 15% slows fermentation, and I suspect this is an
osmotic effect.
 
Good luck, and if you do find any yeast references I will love to
hear about them.
 
Graham Kent
Dept. of Biology
Smith College
Northampton, MA 01063
(413) 585-3820
 
 
Biolabbers:
 
FYI
 
General source books on yeast:
 
Handbook of using yeast to teach genetics. (1991). authors: T. and M.
Manney, Dept. of Physics Kansas State University Manhattan KS 66506.
 
Methods in yeast genetics: a laboratory course manual (1990) authors: Rose,
Winston, and Hieter, Cold Spring Harbor Laboratory Press
 
Susan J. Karcher, Ph.D.
Instructor in Biological Sciences
Purdue University
West Lafayette, IN 47907-1392
 
 
Todd asked about yeast labs.
 
1. To speed up the yeast: Mix yeast in 1 liter water + 20g sucrose (table sugar)
and incubate overnight. This way the yeast are already working for your lab.
 
2. The yeast will remain viable for several weeks in a refrigerator.
You didn't specify the conditions.
 
3. We get good results with all types of yeast.
 
4. You might try an experiment with different [sugar] concentrations to let
students draw the conclusion re: osmosis. We usually use 0.5-2% sugar. Fungi are
amazingly tolerate of high osmotic pressure which is why they grow on jams. You
can probably get away with 10-20% sugar.
 
Christine Case
Skyline College
case@smcccd.cc.ca.us
 

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