Hi to all fellow homebrewers. This document is meant to be a Yeast FAQ and
general yeast information resource. Where possible, I have referenced the
original sources. Almost all of this data was plagiarized from somewhere by me
or others; however, I have not knowingly used any copyrighted stuff. (I was very
careful *not* to check anything for a copyright ;-).) I have altered the focus
of some documents to more accurately reflect what I feel to be the interests of
the *home*brewer. Some of the information is very basic; some, more technical. I
have tried to give a basic introduction to what yeast are, how they affect beer
taste, and the proper handling of yeast. Some portions of the following were
taken from the Wyeast information circular e-mailed to me by David Adams; the
sections pertaining to yeast culturing are adapted from an upcoming book by Dr.
Fix. Dr. Fix also provided the section on the proper method of yeast
rehydration. Most of the information on the "reputations" of the many yeast
strains was collected from the HBD over the years by Doug O'Brien. Many thanks
to David Adams, Dr. George Fix, and Doug O'Brien. I would also like to thank Al
Korzonas for his helpful suggestions on the characteristics of some of the yeast
strains and for his comments and help in clarifying the sections on propagation
and culturing; Conn V Copas for sending me several informative articles clipped
from the HBD and rec.crafts.brewing; and Mike Sharp for directing me to
information about the Yeast Culture Kit people. Others are referenced next to
their contributions (often second hand). Thanks also to the many people who made
small suggestions or requests for clarification. My name is Patrick Weix, and I
am a graduate student in the Genetics and Development program at UT Southwestern
N.B. This document is composed of rampant hearsay and rumor. Any attempts to pin anything on me or my co-conspirators will be resisted. If all else fails I will call your boss and ask him why you are reading the HBD at work instead of grinding out the Fitzsimmons contract. What do they pay you for anyway? Don't you have anything better to do?...
Yeast are unicellular fungi. Most brewing yeast belong to the genus Saccharomyces. Ale yeast are S. cerevisiae, and lager yeast are S. uvarum (formerly carlsbergerensis, BTW S. carlsbergerensis is listed in some places--for example, the ATCC--as a subspecies of S. cerevisiae). Another type of yeast you may hear mentioned, usually in conjunction with weizens, is S. delbrueckii. Finally, many Lambicophiles want me to say that Brettanomyces sp. are also used in brewing; however, I can't think of anything that somebody somewhere hasn't tried to brew a Lambic with :-)!! You may ask, "If all ale or lager yeast are basically the same species, why all the fuss?" The fuss has to do with strain variation. All dogs are the same species, yet no one will ever mistake a Basset Hound for a Doberman (at least not twice :-). Using different strains can add fun and spice to brewing, especially if you have some idea of the differences. I originally put together this guide to catalogue the different affects of different strains. This information is in Section II. Section I outlines the general characteristics of brewing yeast and tries to answer some of the more frequently asked questions about yeast that seem to cycle onto the HBD. Section III explains how the homebrewer can culture and maintain yeast strains in the safety and comfort of his/her own home.
Some yeast strains are more active and vigorous than others. Lager strains in particular do not show as much activity on the surface as many of the ale strains. Most packages provide an adequate quantity of yeast to complete fermentation with varying amounts of lag time depending on strain, freshness, handling, and temperature. If you find it too slow, make a starter as recommended on the package or as listed in Section III.
The slow onset of visible signs of fermentation can be improved by starting fermentation at 75 deg. F (24 deg. C) until activity is evident, then moving to your desired fermentation temperature. A few degrees can make a significant difference without adversely affecting flavor.
The normal temperatures for ale yeast range from 60-75 deg. F (16-24 deg. C) A few strains ferment well down to 55 deg. F (13 deg. C). 68 deg. F (20 deg. C) is a good average. Lager strains normally ferment from 32-75 deg. F (0-24 deg. C). 50-55 deg. F (10-12 deg. C) is customary for primary fermentation. A slow steady reduction to the desired temperature for secondary fermentation gives the best results.
The fermentation rate is closely related to temperature. The lower the temperature, the slower fermentation commences. Fluctuations in temperature such as cooling and warming from night to day can also adversely affect yeast performance.
Attenuation refers to the percentage of sugar converted to alcohol. Apparent attenuation of yeast normally ranges from 67-77%. The attenuation is determined by the composition of the wort or juice and the yeast strain used. Each yeast strain ferments different sugars to varying degrees, resulting in higher or lower final gravities. That will affect the residual sweetness and body.
Really, it's slightly more complex than that (isn't everything ? :-).There's "apparent attenuation" and "real attenuation". The difference comes about because alcohol has a specific gravity less than 1 (about 0.8). Real attenuation is the percent of sugars converted to alcohol. So, if you had a 10% (by weight) sugar solution (about 1.040), and got 100% real attenuation, the resulting specific gravity would be about 0.991 (corresponding to about 5% alcohol by weight). The apparent attenuation of this brew would be 122%! George Fix published a set of equations relating apparent and real attenuation and alcohol content last year. For example, let
Since A and RE are generally not known to us, additional approximations are needed. The following are due to Balling, and have proven to be reasonable. Let OE and be defined as follows:
The apparent attenuation is 75% (from 1.040 to 1.010), the real attenuation is (11.25 - 4.08)/11.25 = 64%. N.B. Most attenuation figures are given in terms of *apparent* attenuation. (Thanks to Chris Pencis quoting Stuart Thomas quoting George Fix).
Flocculation refers to the tendency of yeast to clump together and settle out of suspension. The primary determinant of how well a strain flocculates appears to be the "stickiness" of the carbohydrates in the cell wall. The degree and type of flocculation varies for different yeasts. Some strains clump into very large flocculate. Some flocculate very little giving a more granular consistency. Most yeast strains clump and flocculate to a moderate degree. A yeast that is more flocculant will fall out of suspension better. How does that affect the final clarity of your brew? Well, since it will be in the bottle at least a week before you drink it, it really doesn't seem to matter so much. However, it does matter for other characteristics of the beer, namely attenuation and diacetyl. If the yeast settle out too quickly, they may leave some chemical reactions unfinished. Mostly these strains: 1) May not be as attenuative because of shorter contact time with the sugars, 2) May not finish reducing all the diacetyls, leaving a butterscotch flavor.
Typical pH range for yeast fermentations begins at about 5.1 and optimally 4.8. The pH of wort is usually about 5, depending on the starting pH of the water and the grains or extracts used. During the course of fermentation the pH reduces to typically 3.9- 4.1 and as low as 3.1 in some wines. pH may be checked using pH paper test strips, which are available at many homebrew shops.
The alcohol tolerance for most brewing yeast is as least to 8%. Barley wines to 12% can be produced by most ale strains. Pitching rates need to be increased proportionally to higher gravities. Alternately, Champagne and Wine yeast can be used for high gravities sometimes reaching alcohols to 18%. To get the characteristics of particular beer yeast strains in Barley Wines or Imperial Stouts, some brewers start with the desired beer strain, brew to 5-8%, and finish with a champagne or wine yeast.
Although the principle tastes present in a beer are the result of the malts and hops used, the strain of yeast used can also add important flavors, good and/or bad. Yeast that add little in the way of extra flavors are usually described as having a "clean" taste. These yeast are especially useful for beginners because they permit experimentation with different ingredients without worrying about yeast influence. Yeast produce three main classes of metabolic by-products that affect beer taste: phenols, esters, and diacetyl. Phenols can give a "spicy" or "clove-like" taste, but can also result in mediciny tastes, especially if they react with chlorine in the water to make chlorophenols. Esters can lend a "fruity" taste to beer. Diacetyls can give beer a "butterscotch" or sometimes a "woody" taste. The desirability of any one of these components depends largely on the style of beer being brewed. In addition, there are certain by-products in these families that are more noxious than the others. A lot depends on the individual palette and the effect you are aiming for.
A final note: some yeast, especially lager yeast during lagering, can produce a "rotten egg" smell. This is the result of hydrogen sulfite production. Although the scent of this bubbling out of the air-lock is enough to make the strongest homebrewmeister blanch, fear not! The good news is that this will usually pass, leaving the beer unaffected. Relax, etc.
Most of the dry strains are available by mail-order or at your local homebrew store. Wyeast are also widely available (by which I mean, of course, that my local store carries a wide selection). The BrewTek strains and the Yeast Culture Kit strains are significantly less available, so the company contact numbers are included as a public service.
Please do not confuse the Yeast Lab numbers with the Yeast Culture Kit Company numbers. Both use strain designations with the form A(le)## or L(ager)##, i.e. A06, L01, but they are *completely* different.
Also, a frequently asked question is "how do you pronounce Wyeast?" Well, it's pronounced like "WHY-yeast."
I am deeply indepted to George Fix for both giving me these chapters and letting me alter and condense them for the homebrewer. His support was an essential impetus for getting this FAQ off the ground.
This process consists of transferring some of the yeast on slants to a small flask or jar containing wort, then building this up until there is enough to pitch a full brew. The most delicate steps are the initial ones. Experience has shown that the best results are obtained by using full strength hopped wort for propagating yeast. The ideal situation is when the wort used in propagation is identical to the wort that will be used in brewing.
Practical experience has also shown that it is best to pitch yeast freshly harvested from slants at the maximum acceptable rate. Anticipating the results in the next section, this for lager yeast amounts to pitching 1 volume of yeast solids for each 250 volumes of wort. Thus, we need 5gal/250 = 0.02gal*128oz/gal = 2.5oz of yeast solids for a 5 gallon batch. Using the estimation that yeast solids are 1/10 the total volume of a yeast culture after the krauesen dies down (i.e. just entering lag phase), that means that one needs about 25oz or a little more than 3 cups culture. For ale yeast all of these numbers are reduced by a factor of two, so (3/2) to 2 cups of an ale yeast culture would be sufficient.
In the procedure described below new wort is added just after the end of the period of high krauesen, and in particular after the foam starts to recede. The reason for this is to keep the yeast in the aerobic exponential growth mode. This will insure a steady buildup of yeast cells, and thereby minimize the number of wort charges that are required. The importance of taking great care when adding fresh wort can not be overemphasized. To avoid infections not only is it necessary to properly sanitize equipment, but it also important to sterilize necks of vessels and jars by flame or 200 proof alcohol solutions. The easiest way to flame a jar at home is with a lighter (esp. the ones for pipe- smokers!). Be extremely careful, and don't use both alcohol and a lighter.
The first four steps described below are done under the cleanest conditions possible using 1000 ml. starter jars. At the end of the fourth step there will invariably be more than enough yeast in each starter jar to pitch a 25 liter brew (about 6gal); i.e., there will be at least 1/10 liter of yeast solids as can be checked by visual inspection. These numbers are based on the requirements of lager yeast. As will be seen below there will be no harm in producing too much yeast in this procedure since at the end only the correct amount will be added to the fermenter.
For each jar, start by sterilizing its neck. Then sterilize ("flame") the inoculation loop. Open a slant, quench the loop in clean agar ("sizzle") and use the loop to remove some yeast. Remove the airlock and then add the yeast to the starter jar. Replace the airlock, and then start work on the next jar.
Two steps are needed in the preparation of new slants. The first consists of adding the proper media to test tubes or petri dishes. Once prepared the slants will store well far a very long time when refrigerated, so many can be prepared at one time. The second step consists of inoculating the slants with yeast. For the homebrewer who cannot afford several refrigerators: Please be advised that your refrigerator is a haven for bacteria, mold, and wild yeast. Anyone wishing to store sterile slants in their refrigerator is advised to
The media consists of dry malt extract and agar. As a general rule 4 tablespoons of malt extract and 1 tablespoon of agar per cup of water will yield 16-18 slants.
Note: Plastic petri dishes can not be autoclaved, and so alternate procedures are needed for them. You may use the above techniques with pyrex petri dishes if you so desire. A common practice is to autoclave the malt/ agar solution in small jars or flasks. The agar solution is then poured into the petri dishes. Let the agar cool until the jars are just slightly too hot to handle bare handed--about 50 deg C; the media will start to set around 40 degrees. If the agar is too hot it will warp plastic plates. Swirl it gently to mix but avoid bubbles. A few bubbles around the edges are unimportant, but sometime the whole surface of the plate is bubbles. You can pop the bubbles with the flame of a lighter! Or use a hot inocculation loop. Do not use your finger or blow on the plates. Let the poured plates dry 2 or 3 days in a clean quiet room before bagging. Condensation is normal, but you have to deal with it. Once the plates have cooled, turn them over (agar side on top) and always incubate them and store them in this position. That way the water vapor wafts into the agar and keeps it humid (slightly) and any condensation that does form drops to the lid and can be shaken off. Wipe them down, seal them, and bag them, but leave them at room temperature for 1 week. The bad bugs, if they are there, will be visually apparent at the end of that period and the contaminated plates can be discarded. While Petri dishes are more trouble than test tubes, they do offer the distinct advantage of having more surface area and being easier to store. After the trial period the dishes should be refrigerated.
Another Note: If you find *mold* (not wild yeast) contamination to be a
persistent problem, Pierre Jelenc
From 0.5 to 1% sodium propionate in the medium will suppress practically all molds, without affecting the growth or viability of yeasts. The propionate can be either added before autoclaving, in which case the medium will turn cloudy, or as a sterile solution just before pouring the plates, in which case the medium will stay clear. There is no growth difference in either case. While not reinheitgebotmaessig, propionate is FDA-approved to prevent molds on foodstuffs.Thanks Pierre!
Note: The larger surface area afforded by Petri dishes can be used to advantage in the above procedure. In particular, it useful to streak out yeast in parallel lines which make angles with each other. This allows for a better examination of growth patterns. Petri dishes should be sealed after the 1 week trial period with electrician's tape and refrigerated.
How can you tell contaminants (mold and bacteria) from yeast? J. Wyllie (The Coyote) firstname.lastname@example.org wrote in rec.crafts.brewing in answer to that question: (this has been slightly ammended)
*Things to look for: Colors: creamy off white. (red, yellow, etc likely to be contaminants) Textures/Shapes: Mostly roundish, like a demi-sphere. (Fuzzy=bad mold, flat=maybe bad). Light Transmittance: Hold the plate up to the light. Look for colonies which are transluscent- let light pass. If there are opaque ones (darker) consider them contaminants. You can still pick a pure colony off of a plate with a contaminant elsewhere on the plate (unless you have fuzzy fungal hyphae and spores all over)The main thing is that you want homogeneous growth on the plate. Variation is something to be cautious of.
The following notes were taken from a demonstration given to the Oregon Brew Crew by Dave Logsdon of WYeast Labs, on September 12th. According to Dave, it was important for healthy yeast to be washed free of trub and hop residue so that it could be stored for future use. Dave said that the problem with simply storing the mixed contents from a carboy after fermentation was that the unwanted particulates would suffocate the yeast over a period of time. Most breweries, Dave stressed, use an acid wash; the sterile water wash is much more practical for homebrewers.
- To recover yeast from a finished batch of beer for repitching or storage for future brewing.
- One primary fermenter after beer has been siphoned off or otherwise removed.
- Three sanitized 1-quart Mason jars with lids, half full of sterile or boiled water. They should be cooled down, then chilled to refrigerator temperature (ca. 38^F).
- Sanitize the opening of the carboy (flame or wipe with chlorine or alcohol)
- Pour the water from one of the quart jars into the carboy. Swirl the water to agitate the yeast, hop residue and trub from the bottom.
- Pour contents from the carboy back into the empty jar and replace the cover.
- Agitate the jar to allow separation of the components. Continue to agitate periodically until obvious separation is noticeable.
- While the viable yeast remains in suspension, pour off this portion into the second jar. Be careful to leave as much of the hops and trub behind as possible.
- Agitate the second container to again get as much separation of yeast from particulate matter as possible. Allow contents to rest (about 1/2 hour to 1 hour) then pour off any excess water--and floating hop particles--from the surface.
- Pour off yeast fraction which suspends above the particulate into the third container.* Store this container up to 1 month refrigerated. Pour off liquid and add wort 2 days before brewing or repitch into a new brew straight away.
It should be noted that in the actual demonstration, Dave eliminated the final step; the yeast in the second jar was essentially clean at this stage and seemingly fine for storage.
Rick Cavasin sent me (PW) the following method of "parallel" culturing liquid yeasts. This should work with most packaged liquid yeasts, not just Wyeast. The advantages here for the beginner are that (in additon to saving money) it minimizes the problems of strain drift and contamination that can plague yeast ranchers. As for the savings, it makes liquid yeast almost as cheap as dry yeast!Post follows:
Here's the (poor man's) method for stretching the Wyeast that I (Rick) have been using successfully. This method has worked for me with 4 different Wyeast ale strains (Whitbread, Irish, German, European). It's simple, and requires no special equipment. Also, it allows several brewers to swap yeasts with each brewer propagating one strain.
Briefly, my suggestion consists of converting the original Wyeast package into a number of 'copies' stored in beer bottles. ie. it is a parallel propagation rather than a serial propagation
You will now have about 6 bottles of very thin beer with a good deal of viable yeast sediment in each bottle. Use each bottle as you would use a package of Wyeast - ie. prepare a starter culture a couple days before brewing. This is facilitated by canning wort when you prepare the master starter. All you need to in that case is pop open a mason jar of wort, dump it into a sanitized bottle/jug of appropriate size, pop open one of your bottle cultures, add it, agitate vigorously, and fit an air lock. All yeast starters are of the same 'generation', ie. 'twice removed' from the original Wyeast package (as opposed to the usual 'once removed'). I've had the bottled cultures remain viable for more than 6 months. Observe proper sanitation and wort aeration procedures thoughout. Equipment: 1 gallon jug (for 'master' starter) 1.5 litre wine bottle (for subsequent starters) air lock 6 beer bottles, caps and capper Optional equipment: mason jars and canning pot. Cheers, Rick C.
- Step 1: Prepare some starter wort (S.G. = 1.020), see Miller's book for recipe. Basically, you need about 1/2 gallon, but if you make more and can it in mason jars (using standard canning procedures), you will not have to prepare more at a later date. Note from PW--Most authorities now recommend using full strength (1.040), hopped wort for starters.
- Step 2: Place 1/2 gallon or so of starter wort in a suitable container (1 gallon glass jug), pitch (inflated) Wyeast package at correct temp. and fit air lock. This is the 'master' starter.
- Step 3: Allow to ferment to *completion*. When fermentation has ceased, agitate the 'beer' to suspend all sendiment, and very carefully bottle it.
The following technique is reproduced as is from the pages of the HBD; it sounds like and interesting and useful method. Now, if someone could only figure out how to send yeast by e-mail!
I would like to update this resource periodically, so send me any new techniques, comments on the ones here (good or bad), or opinions on yeast strains. Patrick Weix email@example.com
From: firstname.lastname@example.org Subject: Mailing Strains
... I thought it worth mentioning that there is a cheaper alternative to agar slants for mailing strains, and it works just as well. We routinely send out laboratory strains on filter paper. Basically, you just put a drop of culture on a ~1 cm square piece of filter paper (probably any absorbent paper would do) and wrap the square in a piece of sterile foil. Then pop it into an envelope and send it off. When it gets to the other side, they drop the paper on a rich media plate, incubate for a day or so, and the yeast grow up. Then you streak for singles on another plate and you're set. I haven't rigorously determined the viability of cells dried on paper, but they are very stable. It works.
I can think of two possible disadvantages to this system. First, we use autoclaved paper and foil, and a surprising number of households STILL lack an autoclave. However, while commercial paper is probably not sterile, I imagine it is pretty close; the yeast are going to far outnumber anything else, and when you streak for singles you will get what you want. The foil you could always steam, but probably it would also be close enough to sterile for most people's purposes. The second drawback is that this method requires that you are set up to culture, and to streak for singles in particular. However, while this isn't absolutely necessary in the case of slants, it is certainly advisable. Anyway, just thought I'd throw it out there.Dave Rose Dept. of Cellular and Developmental Biology Harvard U.
This FAQ was HTMLized by Gary Richgaryrich@qdeck.com. I will probably make it more fancy as I can find the time. Let me know what you think.