Original: 2 April 1995
Last Rev: 14 April 1995
Brewers frequently ask about slow-starting fermentations, especially when using liquid yeasts, and are often told they need to use starters. This document gives the details needed to make good starters; the steps provided will ensure perfectly acceptable results if good sanitation practice is followed.
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.
A yeast starter is relatively large, dense population of yeast nurtured and conditioned with one or more feedings of wort. A starter begins when a small amount of yeast (from a "smack-pack", for example) is 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. Usually the term 'starter' refers to 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 making a starter though, the beer produced is simply an unwanted bi-product.
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 yeast are pitched into the primary, the result is often a very vigorous ferment which may start within 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 ensure the yeast dominate the environment over unwanted competitors such as bacteria and wild yeast strains. The use of a starter can allow the brewer to condition the yeast to high gravity worts and to prepare the yeast for the temperatures at which you expect to ferment. Finally, the use of a starter can add some flexibility to your brewing schedule--if you can't brew when planned, the starter can be maintained until you can. The proper conditioning of the yeast also helps reduce production of normal but undesired fermentation by-products, producing better beer. With practice and good recordkeeping, you can prepare your yeast for the best ferment possible.
To avoid confusing the issue with many special cases, let's assume we're starting 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 also begin with a liquid yeast culture fresh from your supplier's refrigerator.
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'
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, I move up to a 1/2 gallon glass jug.
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.
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 frequent skin contact occurs. It's much more expensive than chlorine bleach, but also much easier on clothing and hands. I also feel better about not rinsing with tap water, a source of contamination that may hurt yeast cultivation. Other no-rinse sanitizers may work perfectly well, I just haven't used them.
I'll describe some refinements and modifications of the following overall process, but these five steps summarize making and using starters:
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 other brands 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. The easiest 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. My 12 year old daughter does this--you can too!
Holding the package between your two palms, agitate the contents. You can do this until you're happy the contents are thoroughly mixed. Set the package in a location that will stay at a cozy and steady temperature of about 75F for about 24 hours or until the package has puffed up to at least 1 inch thick, and preferably almost 2" thick.
Opinions differ widely here. Some authorities (including the Wyeast package) say the starter wort should have a gravity of about 1.020 (20), and others prefer to target a 1.040 (40) 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 Vol Wort DME DME Syrup Water ------------------------------------ 8 oz 1 oz 1/4 c 1/3 c 3 cups 1 pt 2 oz 6 tbs 7 tbs 8 cups ---- A convenient choice 1 qt 4 oz 3/4 c 3/4 c 12 cups
NOTE: The water volumes given above are chosen only to permit a decent boil time, with the intention of reducing during the boil to the volumes given in column one. 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 8 cups of water and bring to a boil.
2. Boil the wort until reduced to 1 pint.
Addition of a small quanitity of hops is advised by some brewers as an antiseptic. The amount is not too important--a tablespoon of leaves would be fine. 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 alleged antiseptic property of hops shouldn't be relied on anyway.
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.
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 thermomenter 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 yeast environment closer to the expected beer environment.
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.
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 stoper 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 ferment startup.
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?"
"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 cell membranes. 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
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.
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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