Preparing Yeast Starters
By Mark Tumarkin
At the last meeting Robert gave a terrific presentation on yeast. George discussed the club yeast ranch and showed us how we will receive our "herd" of yeast from the ranch. They will come in a tube similar to a White Labs tube. This will require that you do a starter to increase the number of yeast prior to pitching. A quick show of hands revealed that only about half of us routinely do starters. With that in mind, I thought the following might be helpful.
Preparing Yeast Starters
Kirk R Fleming / Colorado Springs / flemingk@usa.net
Original: 2 April 1995
Last Rev: 12 October 1995
Introduction
You've just chilled your precious wort and pitched the contents of a "smack-pack" of commercial
yeast culture. A day later you still see no activity in your carboy, and you begin to worry.
Another day passes and still no activity. Finally, after three days of this torture you ask
the folks at your local supply shop what's up. "Did you make a starter?", they ask. You reply,
"Did I need to make a starter? What's a starter?".
This little scene occurs over and over again as brewers new to the use of liquid culture yeasts
discover the agonizingly slow starts common with such yeast. This is especially common for
brewers who chill the wort to proper fermentation temperatures rather than using a "hot start".
Here are the details you need to make good starters; the steps given here will ensure good
results if you pay attention to sanitation.
I don't try to answer all kinds of questions about yeast metabolism, growth and propagation,
but I've included some of what authorities say about these topics where it seems helpful.
Please help ensure the accuracy of this information. If you find a problem, please contact me
and we'll get it corrected.
What Are Starters and Why Are They Used?
Making Your First Simple Starter
Improved Starter Development
What Are Starters and Why Are They Used?
A yeast starter is large population of yeast you grow by nurturing an initial culture with one
or more feedings of wort. A small amount of yeast (from a "smack-pack", for example) is
carefully pitched into a pint or more of wort. After a short time the yeast cells multiply,
providing a huge population which is then pitched into the primary fermenter. Brewers often
use the term"starter" to mean both the yeast itself and the wort it is grown in. Making a
yeast starter simply mimics, on a small scale, the process of fermenting a batch of beer. In
the case of a starter, the beer produced is just a bi-product which I call "spent wort" in
this document.
Starters can be made using yeast from a previous brew, from a culture slant, or from a
commerical yeast culture package. The yeast from any of these sources is pitched in a small
quantity (1 or 2 pints) of wort. This process quickly produces 10, 100, or even 1000 times
the yeast provided in commercial liquid yeast packages. When such large, healthy doses of
yeastare pitched into the fermenter, you'll get a very vigorous ferment starting in as little
as 3 hours.
The large yeast population developed with a starter ensures plenty of yeast survive the shock
of specific gravity and temperature changes when pitched into the beer, and helps the yeast
dominate over unwanted bacteria. This 'domination' comes from the fact that a large yeast
population can more rapidly lower wort pH and make alcohol--two things most bacteria can't
tolerate.
When yeast cells are pitched into a high gravity wort, the contents of the cells starts to
migrate through the cell walls to the higher density outside world (osmosis). The yeast cells
respond with a defense mechanism to prevent this loss, using their energy reserves in the
process. Instead of making beer, they're just trying to stay alive. This response is called
"osmotic shock". By first making a starter and adapting the yeast to a high gravity wort, you
avoid osmotic shock--the yeast are ready to make beer instead.
You can also use the starter to add flexibility to your brewing schedule. If you can't brew
when planned, the starter can be maintained until you can. By properly conditioning your
yeast, you help reduce production of normal but undesired fermentation by-products, and make
better beer. With practice and good record keeping, you can prepare your yeast for the best
ferment possible.
One question that frequently comes up is, "How much yeast should I pitch?" Recommendations
don't vary much from source to source: 10 million viable cells per mL of wort. Well, that's
not too helpful for most amateur brewers, but luckily yeast sediment populations are known
accurately enough to give the following guidance: for ale, an adequate pitching rate is 1 US
fluidounce of yeast solids (sediment) per 1 US gal of wort. Barring any mental malfunctions,
I think this is about 10 mL of yeast solids per litre of wort. For lager brewers, this
pitching rate can be increased by 50% as a starting point.
All this discussion of pitching rates also brings up the question of how much yeast is
provided in a commercial liquid yeast culture package. I've measured the quantity of yeast
sediment provided in two Wyeast smack-packs (the standard 50 mL size packages) and found very
close to 1.6 mL. This means that for a standard 5 US gal batch of beer, you need to double the
quantity of yeast 6 times! Let's get started.
Making Your First Simple Starter
Let's start from scratch: you have no yeast cultures in the fridge, no batches of beer
currently in active ferment, and aren't trying to culture yeast from the bottom of that bottle
of favorite commercial ale. Let's begin with a liquid yeast culture fresh from your supplier's
refrigerator. You may find products from BrewTek, Wyeast, or even vials of liquid yeast from
the local university. I'll assume a Wyeast smack-pack; I think the gold foil bags are so common
chances are good you've seen thembefore.
Materials and Equipment Needed
First, here's a list of items you should have prior to making a starter. Following the list I
have some opinions and advice on
three particular items: starter bottles, sugar sources for the wort, and sanitizers.
Airlock with Stopper...............for starter bottle
Clean Saucepan with Lid............to boil starter wort
Clean Tea Strainer (optional)......to strain hops from wort
Dietary or other scale (optional)..the weight ingredients
Dry or Liquid Malt Extract.........food for the yeast
Ice and Container for Ice Bath.....to chill wort
Sanitizer (preferably Iodophor)....to sanitize everything
Small Pair of Scissors.............to open yeast package
Starter Bottle.....................to grow yeast in
Whole Leaf Hops (optional).........to make starter wort
Yeast..............................it's beer we'd be a makin'
Bottles
You need a bottle--one you can easily clean and with a mouth large enough to accept a standard
carboy airlock and stopper assembly. A large mouth is also handy when pouring in the liquid
yeast culture--you can pour it straight to the bottom of the bottle without a funnel. I have
found the optimum starter bottle is shaped much like the traditional Heinz ketchup bottle, but
preferably with a larger mouth. Excellent examples: Smuckers syrup bottles and some barbeque
sauce bottles.
Many brewers use 12 and 22 oz beer bottles and are perfectly happy with them. Both Papazian
and Miller describe the use of such bottles for yeast starters. I don't use them for three
reasons: 1) I then have to keep track of a special, single-purpose small stopper, 2) you can't
see what stage the fermentation is at through the brown glass, and 3) it's difficult to tell
if the bottle is thoroughly clean. You're building a miniature fermenter here--the inside is
going to get dirty. For 2 1/2 and 5 gallon batches of beer I like to use the small pint-sized
starter bottles. When planning 7 3/4 to 12 gallon batches, move up to 1/2 of full gallon glass
jugs.
Starter Sugars
When planning an extract-based beer I just use some of the extract to make the starter. I buy
bulk extract and buy an extra 1/2 lb for $1, and I have plenty of starter material. In the
past, when planning an all-grain brew, I'd buy a 1 lb bag of plain light dry malt extract
(DME). This is very convenient for measuring, but is fairly expensive compared to bulk extract
syrup. If you're an extract brewer and can get syrup in bulk, buy a little extra. If you can
only get canned extract, buy a 3 lb bag of DME to meet future starter preparation needs. See
Preparing the Starter Wort below for instructions to make wort from all-grain. This is a great
opportunity to do an all-grain "brew" with no risk!
The least expensive (and I think the most satisfying) way to get starter wort is to
pressure-can a few pints pulled from each batch of beer brewed, or to simply brew a mini-batch
from inexpensive grain. For those brewers living in the USA, a few pounds of Klages malt will
provide a very low-cost source for wort that can then be canned in one-pint mason jars. The
biggest benefit with this method is the complete avoidance of DME and the associated mess.
During high humidity periods I always have trouble with DME--I prefer to avoid it altogether
if I can!
Sanitizers
I used only Chlorox and water for sanitization until we eventually needed a sanitizer suitable
for no-rinse use with stainless kegs. Now I use Iodophor (iodine-based) sanitizer almost
exclusively. It's handy for equipment that needs to be repeatedly sanitized and when frequent
skin contact occurs. It's much more expensive than chlorine bleach, but also much easier on
clothing and hands. Other no-rinse sanitizers may work perfectly well, I just haven't used
them.
Building the Starter
I'll describe some refinements and modifications of the following overall process, but these
five steps summarize making and using starters:
Process Overview
1. Prepare the yeast.
2. Prepare a small quantity of wort using DME or syrup.
3. Chill the wort and pour in a sterile bottle.
4. Pitch with pure yeast culture, aerate and place an airlock.
5. After high kraeusen, pitch the starter.
Preparing the Yeast
Approximately 1 to 2 days prior to your scheduled brew day, acquire the liquid yeast package
from your brew supply source. My homebrew shop carries only Wyeast liquid yeast, and my
experience is limited to this brand. I speculate otherbrands of liquid cultures will be
similar. In the case of Wyeast's packages, I like to allow the gold package to warm up to
room temperature after getting the package home from the shop. After the package warms up,
smack the package hard enough to break the inner bladder. An easy way is to find the inner
package by feel, place that inner bladder over the palm of one hand, and smack it with your
other fist.
Holding the package between your two palms, agitate the contents until you're happy the
contents are thoroughly mixed. Set the package where it will stay at a cozy and steady
temperature of about 70F until it has puffed up to at least 1 inch thick, and preferably
almost 2" thick.
Preparing the Starter Wort
Opinions differ widely here. Some authorities (including the Wyeast package) say the starter
wort should have a gravity of about 1.020, while others prefer a 1.040 wort. The higher
gravity seems more widely accepted, and it's easy to produce from memory: dry malt extract
provides roughly 40 points of gravity for each pound of malt added to 1 gallon of wort.
Scaling by 1/8 gives 1/8 pound (2 oz) per 1/8 gallon (1 pint).
Malt extract syrup will contribute less gravity for the same weight, but not enough to warrant
re-computing. My opinion is this: accuracy (how close your gravity is to 40) is not too
important. Your precision (how little you vary from brew to brew) is somewhat more important.
In every aspect of a given batch of beer, I like to think I can repeat a success. I like to
control those variables I can control.
The following table is provided for your use in preparing starter wort having an approximate
OG of 40:
Vol Wt Vol Vol
Wort DME DME Syrup
----------------------------------------
8 oz (250 mL) 1 oz (30g) 1/4 c 1/3 c
1 pt (500 mL) 2 oz (60g) 6 tbs 7 tbs ---- A convenient choice
1 qt (1 L) 4 oz (120g) 3/4 c 3/4 c
NOTE: Many folks recommend boiling for 15 minutes, just long enough to ensure sterile wort.
For the first few batches I did, I would pour the boiling wort into a graduated beaker to see
what volume was left, returning it to the pan if I hadn't reached the target. Now I simply
estimate by looking at the liquid level in the pan.
To make a one-pint starter:
1. Add 6-7 tbs of DME or syrup to 3 cups of water and bring to a boil.
2. Boil the wort until reduced to 1 pint.
I no longer use hops in my starters and I don't recommend bothering with it. Your sanitation
during this entire process should be the best you can do--the antiseptic property of hops
shouldn't be relied on anyway.
NOTE: Making wort for use as a yeast starter is a great chance to find out what mashing grain
is all about. If you've wanted to try mashing but feel you don't have the equipment you need,
don't want to commit to brewing an all-grain batch of beer, or are worried about how the beer
would turn out, now is a good time to witness the magic, yea, the splendor of mashing.
For about 3 quarts of wort, buy 1 pound of the least expensive pale ale malt your shop
supplies. In the USA, this will probably be American 6-row or 2-row Klages malt. Also pick up
2 ounces of crystal malt with a color rating of from 20 to 60L. Again, buy the cheap domestic
stuff.
Mix the grain with 2 quarts of water in a saucepan, stockpot, brazier pan or whatever else you
can use to hold it all and to heat it on the stove. Warm it up to about 150F and try to keep
it between 145 and 155F for about 45 minutes. The temperature is not too critical, but don't
let the mash get hotter than 160F for certain.
After the 45 minute mash, strain the liquid through a kitchen strainer, collander, or whatever
you have on hand to get the liquid separated from the grain. Then rinse the grain with about 2
quarts of hot water (140 to 180F is okay). You should now have almost a gallon of water in a
pot, ready to boil. You've just made a all-grain brew suitable for consumption by yeast!
While boiling the wort, sanitize the exterior of the Wyeast package in a sanitizing solution
(B-Brite, bleach, iodophor). You should also have sanitized the starter bottle, the scissors,
and the airlock. I recommend leaving all these things in an tepid iodophor bath until just
prior to use--in which case, do not rinse them.
Some brewers feel autoclaving (pressure-cooking) the starter bottle and stopper is required,
and this step certainly can't hurt. My technique is to ensure the bottle and stopper, scissors
and yeast pouch are completely free of any foreign material and have all been thorough washed
with boiling water (not the yeast pak, of course), then placed in the Iodophor for the 30
minute wort boil.
Chill the Wort
I chill the wort in the starter bottle. If your starter bottle is not a Pyrex lab flask and
you don't want to risk shattering it, chill your wort is another vessel or simply in the pan
you boiled it in. I have an ice-cream maker which includes an all-aluminum, gel-filled chiller. This chiller holds about 1 quart of liquid. I keep the sanitized chiller in the freezer, and pour the wort into it straight from the boiling pot and cover it with a stainless lid. This is an ideal chiller for making starters, and is extremely fast at cooling these small quantities.
After cooling, pour the chilled wort into your sterilized (boiled, pressure cooked, or bathed
in alcohol) bottle. Plug the bottle with the sanitized stopper temporarily.
I check the wort temperature with a pocket mercury thermometer that has been stored in
sanitizer. When the wort is cooled, you're ready to pitch the yeast. If you pitch at 80-85F
there is little to worry about, this product will never be beer; however, it's good practice
to keep moving the starter temperature closer to the expected fermenter temperature.
Pitch the Yeast
Remove the yeast package from the sanitizer and shake off the excess water droplets. Do the
same with the scissors. If you're using a puffed Wyeast package, hold the package upright, and
snip off the upper corner --just enough off to open a 1/8" or so hole in the corner of the
package.
Immediately remove the stopper from the starter bottle, and slowly turn the corner of the yeast
package down into the bottle mouth, ensuring ALL yeast drops in freefall into the bottle. Do
not to touch any yeast to the mouth of the bottle or even near the mouth, if possible. I keep
my face, hair, breath and air currents away from the bottle during filling, and keep the
windows closed. After the contents of the package have been so disposed, quickly fit the
stopper back into the bottle (not tightly).
With a sanitized forefinger, cover the hole in the stopper, and use your hand around the bottle
to ensure the stopper stays in the bottle. Shake the bottle to aerate (repeatedly). Then
remove the stopper, place an airlock in the stopper, rinse the stopper in sanitizer, and fit
the stopper/airlock back into the bottle.
Using Your Starter
Place the bottle in a cozy place (I like the top of the refrigerator which is quite warm).
Activity should be apparent within a few hours, and within 24 hours the yeast should have gone
through high kraeusen. After swabbing the exterior of the stopper and bottle with alcohol or
other sanitizer, remove the airlock and pitch the yeast into your beer. You have greatly
increased the chance of a quick, vigorous startup.
Improved Starter Development
The Concept
You can take extra steps to provide even more liklihood of a proper ferment. So far, we've make
a simple, effective, single-stage starter that probably increases your pitching rate by several
orders of magnitude over the use of just a single Wyeast package, for example. I haven't done
the analysis to determine how many orders of magnitude, but I don't think "several" is an
exageration.
By adding fresh wort to the starter rather than pitching it, an even greater amount of yeast
solids can be produced in one day. I recommend at least one additional feeding for this reason.
In addition, this is also a good practice if pitching into relatively high gravity beers to
ensure sufficient yeast cells survive the stress of preventing the loss of precious cell fluids
through osmosis.
The additional feeding can be done in the original starter bottle if there is enough space left
in the bottle for the added wort. If not, the starter can be moved to a larger bottle. Another
option is to wait for some settling of the yeast, then decant most of the spent wort off the
top and add fresh wort. This allows the use of a single small starter bottle and provides a way
to boost the yeast population without a lot of liquid transfers.
In addition to simply increasing the yeast population, the yeast can also be conditioned over a
few stages to higher gravity worts and/or lower temperature ferments. The basic idea: give the
packaged yeast an environment that poses minimum challenges: a medium gravity wort and a warm
temperature (say 75F). After the yeast population has been bulked up, provide a second feeding
of wort having a gravity closer or equal to that of the OG of the beer you're about to brew,
and begin lowering the temperature to your desired ferment temperature, if applicable. For
example, put the bottle closer to the floor to keep it cooler, or even put it where the
fermenter will be. This should be effective in preparing the yeast for the environment that
counts: the beer.
While discussing the subject of starters on the UK Homebrew mailing list I received a response
from Dr Gillian Grafton, University of Burmingham. Here is the edited transcript:
My question to Dr Grafton:
"A high-gravity task lies ahead for me, and since I usually do a multi-stage starter
anyway, I was planning to start the yeast with a 1.030 wort, move to a 1.060, then finally a
1.090. The reason for so much trouble is the yeast is one I've not used before and I want to
ensure there's both plenty of it and that it likes the environment. During this "staging"
process in the past I've also tried to start a little warm, and gradually move the temp down
(when possible) to the final ferment temperature. As the wort ferments and the gravity comes
down, why doesn't the yeast simply re-acclimate itself to the lower gravity, nullifying any
conditioning? Doesn't the yeast still get some osmotic stress when subjected to a fresh wort
of almost any gravity?"
Her response:
"Yeast can metabolise in two different modes, namely aerobic and anaerobic, for the first
they require oxygen for the second they don't. When you aerate your starter you kick the yeast
into aerobic mode and they respond by growing but not fermenting. Once the oxygen is depleted
they stop growing and start into anaerobic mode and at this point the fermentation begins.
The point is, in the phase in which you grow up your yeast no fermentation has yet
proceded, so the yeast grow in a way which is appropriate to the starting OG and osmotic
stress of the wort starter. The yeast adapt to high OG and osmotic stress by synthesising
different levels of certain cholesterol derived lipids in their cellmembranes. When the
fermentation begins after growth is completed the yeast possess the appropriate level of these
lipids in the cell membranes and this does not change throughout fermentation. Therefore, at
the end you still have yeast adapted to your original OG and osmotic stress level. If you step
up in gradual stages, you gradually build up the lipid levels in the cell membranes so the
final pitch into a high OG is not a rude shock and is well within the cell endurance capacity.
If you hadn't have adapted the yeast then the levels of these lipids would be low and the
resulting stress could see the yeast off into oblivion, or at the least would result in a lag
whilst the yeast synthesised the protective levels. There is always a certain amount of shock
when transferring from one OG wort to another, but you can minimise the damage by adapting the
yeast in advance."
Dr Gillian Grafton / GraftonG@novell2.bham.ac.uk
Department of Immunology
University of Birmingham
Birmingham, UK
One Suggested Process
So far, we've built a small starter that has increased the yeast solids volume from what the
manufacturer provides in the smak-pak (a volume equivalent to that of a 5 cent piece) to
possibly as much as 8 cc. Since the wort volume is very small, the entire bottle contents can
be pitched with no concern for changing target beer volume or influencing beer flavor. But
let's bulk up!
The starter can be moved to a clean 1/2 gallon glass jug and fed with about 1 quart of wort to
tremendously increase the yeast. Using the table above, prepare and chill the wort. After
chilling, pour this wort into the sanitized 1/2 gal jug, fit a stopper and aerate by shaking
repeatedly.
If the yeast in the smaller starter bottle has settled out on the bottom to a distinct layer,
then decant nearly all of the spent wort out of this bottle, swirl the remaining contents to
bring the sediment into suspension, and pour the contents into the new 1/2 gallon starter. If
the small starter appears very cloudy indicating little flocculation has occured, then just
pour the entire contents into the new starter bottle. In either case, fit a stopper to the jug
and aerate by shaking vigorously. Then fit the sanitized airlock to the 1/2 gallon jug.
Again, wait for the yeast to go through the period of maximum activity if you can. Depending on
when you must brew, the yeast will be suspended or precipitated, or somewhere in between. If,
at pitching time, I find the yeast has settled out almost completely, I decant the spent wort
and pitch mostly the sediment. If I have to pitch at or around high kraeusen, then I dump the
entire starter contents into the beer.
For 6-10 gallon batches, one quart of starter won't have too much taste influence, in my
opinion, but I always try to time pitching to avoid adding this much wort. Plan your process
to pitch late rather than early. If you can pitch several hours after high kraeusen, many ale
yeasts will have begun settling out. You can clearly see the extremely cloudy lower layers
under the clarifying upper layer of wort, and can decant the top half or so. This will still
leave the vast bulk of yeast solids for pitching and minimize any flavor contributions of the
starter wort. If you decant into a sterile vessel, even a tiny vial, you can perpertuate this
yeast for many more brews. A few tablespoons of this wort contains far more yeast than came in
the original yeast package.
Summary
The use of a well-built yeast starter has many advantages over the use of yeast straight from a
liquid yeast culture pack. One can easily make a simple starter to enjoy these advantages, or
can take a few extra steps to get increased pitching rates or yeast tolerance for large batches
or high gravity brews. No expensive or unusual lab equipment is needed, and in fact you can do
just fine with things you probably already have around the house.
While the use of starters has real advantages for the beer, it also gives you, the brewer, more
flexibility with your brewing schedule. You can easily maintain the starter with regular
feedings, keeping it poised for action on short notice. While you may not be able to pitch at
the ideal time, you will have an ample reserve of yeast which can be pitched when you need to.
Finally, the proximity of your starter to the original pure lab culture means you have a very
clean source of yeast for propagation. Without exploring the fun and excitement of culturing
on slants, you can still enjoy a nearly limitless and pristine supply of a key material for
beer.
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