A yeast starter will insure that your beer has the best possible chance of turning out well. You will need to build one:
If you want a your yeast in optimum health, if you want to reduce the lag time (and the chance for bacteria to take hold) and if you want consistent and reproducible recipes, you should make a yeast starter.
The cell count numbers can be confusing. If you really want to understand cell counts and pitching rates, go to MrMalty.com and check out Jamil's Proper Yeast Pitching Rates article. Both Mr. Malty.com and WyeastLab.com have pitching rate calculators. If you love to crunch the numbers that's great. For me, I like to use all the tools available to me. Use the calculators and know how much yeast you need to be pitching. It's one of those details that takes you to the next level as a homebrewer.
So how much yeast do I need to pitch? Well, 2000 ml will more or less double the amount of yeast in a vial or packet. Using a stir plate will increase those results dramatically. Trust the calculators and grow your yeast accordingly. As a ballpark figure, use 6 ounces of light DME to 2 quarts of water. This will give you approximately a 1.040 SG wort.
If you have a scale that weighs in grams, even better. This makes the measurements easier and more precise. Figure a factor of 10. For a 1000 ml, use 100 grams of DME (100x10=1000). For a 2000 ml use 200 grams of DME and add enough water to make 2000 ml of wort (200x10=2000).
This x10 ratio will produce a wort with approximately a 1.040 SG. Do not grow yeast in high gravity worts, it stresses the yeast. Keep the fermentation temperature around 70-72 degrees F, a little cooler for a lager yeast.
There are several reasons that you wouldn't want to pitch a large starter into your wort. One is that a large amount of wort, over a gallon, will dilute your OG, your color, and your specialty malts and adjuncts. The large starter will contribute unknown flavors to your beer, especially if it is fermented at warmer temperatures producing unwanted esters, polyphenols, and who knows what other flavors get into the starter beer. I don't usually taste mine to see if it is any good.
According to Jamil and Dr. Chris White from White Labs on the podcast entitled "Homebrewing Saison" originally aired on 09-18-2007, the yeast must go through a growth phase so it can produce the enzyme alcohol acetate transferase (AAT). Esterification of alcohol is controlled by this enzyme. Thus, more AAT means more fruity esters in your beer.
Pitching too much yeast, such as when you reuse the entire cake from a previous batch, will cause the yeast to have a very short lag phase with very minimal AAT production and thus very little ester production.
For some beers, especially those from Great Britain, this makes an uninteresting example of the style. Some beers must have some fruity esters to fall within the BJCP guidelines for that style.
If you find your beers need more esters, try pitching on the low end of the scale for that style so the yeast have a chance to grow and produce the fruity esters you expect
Most brewers like to pitch their yeast when it is at it's height of activity, or full krausen. According to Wyeast Labs, this will be between 12-18 hours. This works out well for most homebrewers. You can make your starter the day before you brew and it should be ready to pitch when your wort is ready.
If you want to pitch the yeast only, with no fermented "starter beer", you will have to let the yeast attenuate fully. After it has finished fermenting, turn off your stir plate and allow the yeast to settle or place the flask in the fridge and it will settle faster.
Pour off the "starter beer" above the yeast leaving just enough to get the yeast into suspension. Just make sure that the yeast is within 15 degrees of the wort temperature when you pitch. This means that if you put your yeast into a fridge, take it out and allow it to equalize to the same temperature as the wort before pitching.
The equipment you need to make yeast starters is minimal. You can make them by boiling the wort in a pot, cooling it in an ice bath, then pouring it into a sterilized quart jar. The easiest way is with a borosilicate glass Erlenmeyer flask (Pyrex, Bomex, Borosil, etc.).
They come in all sizes but the ones you want are 1000 ml, 2000 ml, 3000 ml and for really big batches, 5000 ml. I sometimes make my yeast starter wort in a pot and transfer after cooling to a sanitized gallon jug when I need a really large starter, or when my largest flask is being used elsewhere.
You can boil the wort directly in the borosilicate flask and eliminate the transfer step from a pot to a jar (less chance of contamination). A stir plate is not essential, but most experienced homebrewers either purchase one on ebay, their local homebrew supply store, from an online store, or they make their own.
Here is a good youtube video by a gentleman named Beer Mumbo on how to make a stir plate using a cigar box. You can use other boxes as well, just use your imagination.
You will also need either a foam stopper or aluminum foil to cover the top of the flask while the yeast is fermenting, or you can use a stopper and an airlock. If you use a stir plate, you'll need a magnetic stir bar.
You will also need a way to aerate or oxygenate the wort before pitching. There are several options here, aquarium pump and air-stone, pure oxygen, or just agitating or swirling the wort every time you walk by.
Don't over oxygenate with pure oxygen, around 10-15 seconds should be adequate. And lastly, you need to add 1/4 tsp of yeast nutrient. You can use a couple of hop pellets if you choose, but it's not necessary.
If you are not already making a yeast starter, you really should start. By pitching a large, healthy yeast starter into your wort, you will notice a definite improvement in your beer. In fact, I would go so far as to predict that you might even go from average to award-winning homebrew. This is one of the easiest and most important things you can do to improve your fermentations. Happy yeast makes better beer.
References: Information for this article came from Jamil Zainasheff's website Mrmalty.com, from How To Brew by John Palmer, and from my own experiences making and using yeast starters.
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