Making a Yeast Starter
The Yeast Starter
A yeast starter is a method of preparing your yeast for fermentation by introducing your yeast to a small amount of wort before fermentation in order to encourage yeast cell multiplication to create an optimum amount of healty, ready-to-go yeast cells for an ideal fermentation of your beer.
How Much Yeast do I Need?
As an average, you need about 3.75 billion yeast cells for each point of OG for about 5 gallons of ale wort1. Lager fermentations will require a bit more due to
the extended fermentation and generally cooler temperatures. This means that, for a 1.060 ale, you would need about 225 billion yeast cells for optimum fermentation
conditions. To compare, an average tube or pack of liquid yeast has abut 100 billon cells. So, as you see, you're going to need to increase this yeast count if you plan
to pitch one tube of yeast.
As a rule, the larger the starter, the more yeast reproduction due to the fact that there are more sugars for the yeast to use as fuel for reproduction. As another general principle, a 2-liter starter will approximately double your yeast count1 (with varying conditions taken into account including the amount of oxygen present in the starter.)
There are mathematical formulas and researched-based ratios to calculate all this exactly. However, there is a much easier way. Jamil Zainasheff has written a great tool for calculating starters on his website : the Mr Malty's Pitching Rate Calculator. I encourage you to use this tool and try various scenarios with different OG values and different starter configurations to see how the starter procedures affect the final cell count.
I plugged in 5.25 gallons of 1.060 ale wort using a stirplate aerated starter and found out that I would need to make a 1 liter starter from one vial of yeast in order to produce about 219 billon yeast cells.
Prepare the Starter Wort
First thing's first, we're going to need some wort to use in our starter. By far, the best food for yeast that is going to be consuming wort in the very near
future is, you guessed it, wort. I say this because you may, at some point, have the idea that you can just use table sugar for your starter. This is a bad idea
because the yeast will become accustomed to consuming the simple sugars in table sugar and when it's time to eat up all those beer sugars (maltose, etc.) they will
not take to the idea very well and may drop out of the fermentation before the job is done. Think of this as having to drink a Bud after having a great, homebrewed
beer - you wouldn't want that and, in a way, it's the same with the yeast.
The best source of easy-to-prepare wort is dried malt extract (DME.) You will need enough DME to prepare a starter of about 1.040 OG. A higer gravity, regardless of the beer you're going to make, is not better as the higher gravity will stress the yeast more than is needed for simple propagation and will leave your yeast in bad condition for the fermentation itself. To achieve the proper gravity, you will need about 6oz (by weight) of DME for every 2 quarts of water1. That equates to roughly 3oz. of DME for every 1000ml of starter water you use.
Do bother to weigh out your DME with that same scale you weight you hops with (you do have one, right?) as differing amounts of moisture in different DME brands might make 1/2 cup of one brand contain much more or less than 1/2 cup of another brand in terms of volume measurement.
The next thing you will need is a container. The best piece of equipment for starters is an Erlenmeyer flask made of borosilicate glass. These are able to withstand very high temperatures and temperature swings, are equipped with volume measurements, and have a flat bottom for use with a stir plate. If you do not have an Erlenmeyer flask, the next best thing is a growler from your local microbrewery. Failing that, any glass container that can be covered with an airlock, stopper, or piece of foil will do.
To prepare the wort, weigh out your DME and add the volume of declorinated water (plus a little more to take evaporation into account) to achieve your desired starter volume either directly to the Erlenmeyer flask or to very clean and soap-free pot. Your Erlenmeyer flask can be placed directly on the stove. However, a word of caution, if the volume you are making does not provide enough headspace for the hot break material when your wort comes to a boil, it will be one nasty boilover and one messy stove. You can always boil some water on another burner in your flask while you're boiling your wort for the sake of sanitation.
Boil the wort for about 15 minutes, remove from heat, and cover immedately as sanitation is now ultra-important. Cool your coverd wort to a reasonable temperature and, if needed, transfer to your sterilized starter vessel.
The temperature of your starter should be kept roughly the same temperature as you plan your fermentation to take place. Once your wort is at that temperature, sanitize your yeast packet or vial, the top of your starter container, and anything else like a funnel that might come into play here then pitch your yeast into the starter. If you are using a Wyeast smack pack, you can smack it to add a bit of yeast nutrient into the mix. If you don't that's fine too as the yeast is in the big container, not the little pillow in these systems.
Finally, make sure to cover your starter vessel. You can use a stopper and airlock, or a foam insert that they sell at Northern Brewer. I personally use a piece of loose-fitting aluminum foil that I place on the top of my Erlenmeyer flask while I am boiling the wort (or water if just sanitizing) to ensure that the foil is sanitized. Bacteria, dust, and whatever else in the air that may affect your starter wort falls down, not up, so anything that covers the opening of the starter container and let's CO2 escape during yeast activity should be sufficient.
You may be tempted to add some hops into your wort as well, knowing that they do have some anti-microbial properties and, after all, it's a mini beer. This really is not necessary and, if you are worried about sanitation, put extra extra effort into making sure that each and every thing that comes into contact with your starter is sanitary. If you want to add anything to the wort, some yeast nutrient would be appropriate to encourage optimum growth conditions.
Oxygenate your Starter
Actively reporducing yeast need available oxygen to be able to reproduce and build strong, healthy cell walls. The presence of sufficient oxygen (8 to 16 ppm2)
will allow the maximum amount of cell reproduction - the ultimate goal of the starter process. Oxygen can be provided to a starter in many ways, including the introduction of pure
oxygen. If you do have an oxygenation system that you use for your wort, I would caution the use of this in the small volume of a yeast starter.
I know some people do this with reportedly good results, however it is my opinion that the risk of killing your yeast in the starter solution may be far greater than then benefits.
The first way to more safely introduce oxygen into your starter is by simply shaking the starter as often as possible (for example, hourly.) This method is free, simple, and while the least effective of the methods I will mention, is much better than no oxygenation method at all.
A better method is the use of an aquarium air pump with a sanitary air filter inline and a bubble producing stone that is placed into the starter. All tubing and stone should be sanitized prior to introduction to the starter. This method produces agitation of the liquid which breaks up the surface and allows air/oxygen to be introduced to the solution. This method is reported to be better than periodic shaking.
The best method, albiet the most expensive, is the use of a laboratory stirplate to create a whirlpool effect in the starter. This method provides constant, gentle oxygenation and encourages the most cell reproduction of the three methods mentioned.
To illustrate the differences, I used the Mr. Malty Pitching Calculator again on a 1.060 wort but compared the volumes required to produce that same 220 billion yeast cells with different aeration methods. With a plain starter, no aeration, a 2.43L starter is required. With agitation, a 1.4L starter is needed. With aeration, a 1.22L volume is required and with a stirplate, only 1L of starter volume is required to produce the same number of cells. So, the correlary of this is that, with the same volume of starter wort, more cells are produced with better oxygenation methods.
When to pitch
After a few hours, you should see some bubbling and evident yeast activity going on in your starter. There are two schools of thought on when the best time to
pitch your yeast might be. One way of thinking is that you should pitch the entire yeast starter into your beer wort when it is a high krausen (anywhere from 8 to 18 hours) as the
yeast is actively eating sugars and is ready for more. Another way of thinking about this is that you should pitch the yeast portion of the starter after it has
completely fermented the starter sugars and has had a day or two to build up its cell reserves.
I see both sides of this and, for me, it boils down to which method fits into my brewing schedule best. If I think ahead enough to prepare a starter a few days ahead and allow ample time to settle out, great. If I think of preparing the starter the night before or even the morning of the brew day, I can pitch at high krausen.
With all this said, a yeast starter is not necessary to make a good beer. If you read this and find that it's too much to mess with for your
brewing abitity or you are not one who takes great precautions with sanitation - no worries. Pitch your yeast vial or smack pack as-is and your
beer will likely end up just fine. The activity of producing a yeast starter is just one more tool in your toolbox to make even better beer.
Above all, enjoy your homebrewing sessions and drinking your hard earned beer.
1. Zumurgy - March/April 2007 - Making A Starter by Jamil Zainasheff (pp 21-25)
2. How to Brew - 3rd Edition by John Palmer