NOTE: you should only make a starter with and/or reuse liquid yeast.  Dry yeast does not react the same way as liquid yeast to multiple generations.  In addition a pack of dry yeast tends to have more yeast cells in it than a smack pack.  Freshness still applies to dry yeast (fresher is better) and you will still want to store it cool.

Most experienced brewer's would agree that after sanitation, yeast is the most important factor to making great beer. If you do not pitch enough good, clean and healthy yeast, your beer will most likely have problems in the way of phenolic off-flavours (these can be spicy, medicinal, plastic, smokey and just not very good in general) production of higher alcohols (this gives a hot, solvent like taste), under attenuation and more likely chance of infection.  All things that can lead to beer being slightly off to completely unpalatable.

So the idea is to pitch healthy yeast, and enough of it for the beer you are making.  I'll discuss each part separately.

Healthy Yeast

Healthy yeast is yeast that is clean and free from contamination (of wild yeast or bacteria) and that has a good viability rate.  Any yeast bought commercially (from Wyeast smack-pack or dried yeast package for instance) will be clean.  If you've obtained yeast from a previous batch of beer or another homebrewer, you have to be careful that the yeast is not contaminated.  The only way to determine this is to ensure you know how the beer and yeast has been treated.  If it's your yeast, make sure that you've been meticulous in your sanitization routine, and if it's another brewer, you'll have to trust that they have been as careful.  If possible, taste the beer that you are reusing yeast from.  If it's got off-flavours or tastes infected, throw out the yeast and do not reuse it.

The next major component of healthy yeast is the viability.  Yeast is a living organism, and as such, is more active when fresh.  As yeast sits in a package the cells begin to die and autolysize or self-destruct.  The storage conditions can play a major factor in how quickly this happens.  Yeast should always be kept as close to freezing as possible, without actually freezing.  This will slow the degeneration of the yeast down.  Yeast kept warm (room temperature) will die off a lot quicker.  Even under proper storage conditions, you should probably be suspect of yeast that is 6 months or older.  It can still be revived and used with good results, but it requires a bit more attention than fresher yeast.

Pitching Rates

So now that you know what healthy yeast is, the next major factor is pitching enough yeast.  While Wyeast smack packs are marketed as the proper amount for a 5 gallon batch, they rarely are.  Obviously a bigger batch size will require more yeast, and also, a stronger beer (higher original gravity) also requires more yeast.  The typical pitch rates that give good results are shown below (courtesy of Wyeast Labs).

A Wyeast smack-pack contains 100 billion cells which will translate to a pitch rate of just under 6.00 million cells / ml for a 5 gallon batch.  As you can see from the above table, this is the low end of the scale for an ale with OG below 1.060.  For any lager or ale above 1.060 this is not enough.  Also, the more days that pass from the smack-pack's manufacturing date to the date that you use it, the less cells there will be (again, this is highly dependent on storage conditions).  So in a perfect world, a smack pack is enough yeast, but in practical usage, you are under pitching.

So what can be done about this?  The easiest thing to do (albeit probably the most expensive as well), is to simply pitch more smack-packs.  Pitching two or even three smack packs (depending on the OG of your beer) will provide better pitching rates.  A more frugal approach is to make a starter.

Making a Starter

There are lots of good tutorials for making a starter on the internet.  I'll briefly describe the process, but for more in-depth information check out the links at the end of the article.

Process for making a starter

1. Determine how big your starter will need to be.  You can use a pitching rate calculator to determine this, but in general a 2 litre starter should be good for more moderate strength beers, and if you are doing something big (>1.070) you might want to bump it up to a 4 litre (1 gallon) starter.
2. Prepare enough wort for your starter to an OG of 1.030 to 1.035.  This OG is perfect for growing yeast.  Any higher and it starts to put strain on the yeast, and any less and there is nothing for them to ferment.  The easiest way to prepare this wort is to use 90 grams of Dry Malt Extract (DME) per litre of water (or 3oz per quart).
3. Boil the wort for 10-15 minutes then cool it down to pitching temperatures (I do this by putting the pot in the sink with ice water).  You do not need to add hops to this wort.
4. Transfer the wort to a clean, sanitized container (1 gallon glass jugs work great) and pitch the yeast.  Remember to aerate the wort by shaking and splashing the cooled wort as much as you can.
5. Put an airlock on the container and let it ferment.  You can shake or swirl the starter around during fermentation to make sure the yeast stays in suspension.  Normally you would want to avoid any splashing in a fermenting beer, but the starter beer will be tossed so don't worry about it.
6. When it's done fermenting, let the yeast drop (putting it in the fridge can speed this up) and then pour off the clear wort leaving a slurry in the bottom of the jug.  Swirl this around to release it and pitch it into your big batch of beer.
7. Enjoy the great beer that results.

Tips

Here are some tips that can speed up the process of making a starter (even though it's not that much work to begin with!).

• If you are like me and extremely lazy, the easiest way to make a starter is to purchase a Big & Easy Beer Kit (the 2L bottle beer kit) from the homebrew stores and either pour the wort into a glass gallon jug, or ferment directly in the bottle.  Throw away the yeast capsule, pitch your smack pack and put a real airlock on the bottle instead of the one that comes with it.  Too much carbon dioxide is harmful to yeast, so you do not want the bottle to get carbonated.
• Some people actually prepare a batch of wort, and can it in mason jars for later use.  There are lots of tutorials on the web about this and there is a bit of debate about the risks of botulism with this.  If you do this, make sure you research it well and my advice would be to definitely always use a pressure canning method since wort is relatively high-pH for canning.

If you have other tips or experience with yeast and/or starters, please let us know by emailing This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Resources

Making a yeast starter
http://www.howtobrew.com/section1/chapter6-5.html
http://www.beersmith.com/blog/2008/04/01/making-a-yeast-starter-for-your-home-brew-beer/

Determining Pitching Rate
http://www.wyeastlab.com/hb_pitchrate.cfm
http://www.mrmalty.com/calc/calc.html

Canning Wort
http://www.alsand.com/beer/yeast/cann_E.html
http://www.bodensatz.com/staticpages/index.php?page=20020502172306861