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Preparing Yeast Starters Kirk R Fleming / Colorado Springs / flemingk@usa.net Starters 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. 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 yeast are 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 recordkeeping, 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 fluid ounce 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 them before. 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 Dry or Liquid Malt Extract.........food for the yeast Ice and Container for Ice Bath.....to chill wort Sanitizer ...................to sanitize everything Small Pair of Scissors.............to open yeast package Starter Bottle.....................to grow yeast in 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. (A scientific glass flask is best!), but for our purpose, a 1/2 gal jug will work! MW) If you are making multiple starters, see other article. MW 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). 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 cups of DME will provide a very low-cost source for wort that can then be canned in one-pint mason jars. 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. *Note: Iodopher is a strong sanitizer, NOT a sterilizer! Clorine will Sterilize, that’s about 10x cleaner than sanitized! MW 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 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. 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. (This guy went on for days about this crap, just follow the following info!)MW The following table is provided for your use in preparing starter wort having an approximate OG of 1.040:
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 2.2 cups of water and bring to a boil. 2. Boil the wort until reduced to 1 pint. 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. 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. Home |
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