If you're using dry yeast from a packet, you can basically skip this post. The reason, given below, essentially boils down to the fact that if you're making a normal gravity brew, one packet of dry yeast has enough viable cells to start a healthy fermentation. If you're using liquid yeast, for example from Wyeast or White Labs, or using a small number of yeast either from a frozen vial or used yeast cake, things get more complicated than simply dumping the vial or package into the wort. While dry yeast offers a number of strains to generally get the job done for a number of base styles, liquid yeast offers an astounding number of strains with differing tastes, attenuations, speeds, optimal temps: basically everything needed to tweak a recipe. I've used some theoretical data below from MrMalty and YeastCalc as examples for using liquid yeast and how/why to build a starter, which both are backed up by empirical data. Whatever. Graphs. How can you argue with that?
Yeast Viability
Yeast viability is what determines if you need to prep more yeast or are good to go. Viable means healthy, live cells, and it differs over time and the form yeast are stored in. The graph below gives us a place to start, the recommended number of viable cells needed to pitch into a beer with a certain gravity. We'll assume a batch is 5 gallons.
As you can see, the number of cells needed for a proper pitch varies with the amount of sugar in the beer. While this is a guideline, as a homebrewer you really can't pitch too many cells. If you do, what you may get is a very active fermentation, but not a bad beer. It's not cheap to make a huge yeast starter, so going by these guidelines is a good starting place.
For these examples we'll use an average wort gravity of 1.055, or a pitch of 200 billion cells.
Ok, yeast viability. I mentioned before that dry yeast generally has more viable cells per packet and last longer in storage than liquid yeast, based on the process by which they are stored. The graph below demonstrates the viability of dry and liquid yeast from date of manufacture.
As you can see, dry yeast packets (11g) generally do not lose a lot of viability over time if stored at 4C, and is a good amount for pitching to our example beer. Liquid, on the other hand, starts at 100 billion at the date of manufacture (half the recommended pitching rate), and decreases steadily over time. In fact, given a package date at 3 months past manufacture (what you may find at your homebrew store), the number of viable cells may only be around 32% of the total, which is only around 16% of the number of cells you should pitch for a healthy fermentation! White Labs and Wyeast will disagree, and to a point, they are correct. Pitching this amount into a 5 gallon batch will make beer, and it may be fine, but the time it takes for the population to build invites bacterial infection outbreaks and stresses the yeast to the point that off flavors might develop. To build up a healthy, larger population, the answer is a yeast starter.
The Yeast Starter
There are a number of ways to go about making a yeast starter, some easy, some complicated. Since I've only ever done it one way, I'll go into that. Basically, you want to take the starting yeast population and grow it using pre-boiled wort from dry or liquid malt extract. The real trick is how you help the growth along. Below is the basic setup for a starter.
100g (3.5 wt oz) dry malt extract (or 4 wt oz of liquid extract)
1/2 tsp yeast nutrient
1 Liter water
Glass jug, mason jar or erlenmeyer flask big enough to hold around 2-4 Liters
Sterilize everything that you will use to make this starter. Boil the water with malt extract for 10 mins or so. Cool it to room temp and you're now got a simple wort around 1.035 specific gravity. I usually make a gallon of the stuff and sterilize it using a pressure cooker in mason jars so I can have some ready whenever I need it. The amount of wort that you make and when depends on how you will grow the yeast.
Yeast Growth
Using the assumption that we will be using these yeast for a 1.055 gravity 5 gallon batch, we'll need around 200 billion cells. There are 3 basic strategies that most people use to grow a starter:
Simple Starter (No Shaking) - Basically you add the yeast to a certain amount of starter wort, and let the yeast grow on their own. This is the least effective method to grow a good population.
Intermittent Shaking - Strangely enough, simply shaking the culture whenever you walk by it effectively increases the amount of yeast per volume of wort. Obviously, it depends how often you walk by, but the idea is to keep the yeast suspended as often as possible.
Stir Plate - Using a lab-type magnetic stir plate, you use a magnetic bar that spins in the wort and constantly keeps the yeast suspended. This greatly increases the cell count per volume, and can be found relatively cheaply on Ebay, or you can make your own.
The graph below gives you an idea of how many cells you might have using a simple 1-step starter, meaning you use say 2 Liters of wort, dump your package of yeast into it and do nothing else beyond the the above scenarios.
Essentially, if you shake the flask once in a while, you'll need around 4 liters of starter wort for our theoretical beer. If you use a stir plate, you only need 3 Liters or so. Not a huge difference, but wort ain't cheap either.
Now a way you can increase cell count given a certain volume of wort by increasing the cell density in the wort by chilling the yeast and decanting the used up wort after the yeast have eaten all the sugars (usually take a few days). These are called steps, and I've laid out the same specs below, using 1.75 Liters total at steps of 0.25L, decanting then adding 0.5L and growing, decanting all that and adding 1L and growing it up.
Instead of using 4 Liters through intermittent shaking, you only need 1.75L of starter wort if you use these steps. It might take a bit longer, if you include the overnight chills to decant the used wort, but you've essentially cut your wort in half. Using a stir plate essentially allows you to use less wort overall, so it's something to be considered. It also grows a lot faster as well.
Beyond using a hemocytometer and a microscope to actually do cell counts to confirm your growth, you can monitor your starter using a hydrometer. You'll likely see a final gravity around 1.010-1.015 once the yeast have gone through it.
Culturing Yeast
A good way to save money for brewing is to keep your yeast stored. There are 2 main ways to do this, either keeping frozen cultures or plating on agar plates or washing the yeast from your last batch of beer. Washing yeast is really easy, and if you have room in your fridge for a few mason jars, you can easily save $7 per brew, and immediately start with enough yeast without the need for a starter. You can get about 5-6 generations out of a pack of yeast, so if you do the math that's about 30 5 gallon batches per pack! I'll get into both of these techniques later...
Yeast Viability
Yeast viability is what determines if you need to prep more yeast or are good to go. Viable means healthy, live cells, and it differs over time and the form yeast are stored in. The graph below gives us a place to start, the recommended number of viable cells needed to pitch into a beer with a certain gravity. We'll assume a batch is 5 gallons.
As you can see, the number of cells needed for a proper pitch varies with the amount of sugar in the beer. While this is a guideline, as a homebrewer you really can't pitch too many cells. If you do, what you may get is a very active fermentation, but not a bad beer. It's not cheap to make a huge yeast starter, so going by these guidelines is a good starting place.
For these examples we'll use an average wort gravity of 1.055, or a pitch of 200 billion cells.
Ok, yeast viability. I mentioned before that dry yeast generally has more viable cells per packet and last longer in storage than liquid yeast, based on the process by which they are stored. The graph below demonstrates the viability of dry and liquid yeast from date of manufacture.
As you can see, dry yeast packets (11g) generally do not lose a lot of viability over time if stored at 4C, and is a good amount for pitching to our example beer. Liquid, on the other hand, starts at 100 billion at the date of manufacture (half the recommended pitching rate), and decreases steadily over time. In fact, given a package date at 3 months past manufacture (what you may find at your homebrew store), the number of viable cells may only be around 32% of the total, which is only around 16% of the number of cells you should pitch for a healthy fermentation! White Labs and Wyeast will disagree, and to a point, they are correct. Pitching this amount into a 5 gallon batch will make beer, and it may be fine, but the time it takes for the population to build invites bacterial infection outbreaks and stresses the yeast to the point that off flavors might develop. To build up a healthy, larger population, the answer is a yeast starter.
The Yeast Starter
There are a number of ways to go about making a yeast starter, some easy, some complicated. Since I've only ever done it one way, I'll go into that. Basically, you want to take the starting yeast population and grow it using pre-boiled wort from dry or liquid malt extract. The real trick is how you help the growth along. Below is the basic setup for a starter.
100g (3.5 wt oz) dry malt extract (or 4 wt oz of liquid extract)
1/2 tsp yeast nutrient
1 Liter water
Glass jug, mason jar or erlenmeyer flask big enough to hold around 2-4 Liters
Sterilize everything that you will use to make this starter. Boil the water with malt extract for 10 mins or so. Cool it to room temp and you're now got a simple wort around 1.035 specific gravity. I usually make a gallon of the stuff and sterilize it using a pressure cooker in mason jars so I can have some ready whenever I need it. The amount of wort that you make and when depends on how you will grow the yeast.
Yeast Growth
Using the assumption that we will be using these yeast for a 1.055 gravity 5 gallon batch, we'll need around 200 billion cells. There are 3 basic strategies that most people use to grow a starter:
Simple Starter (No Shaking) - Basically you add the yeast to a certain amount of starter wort, and let the yeast grow on their own. This is the least effective method to grow a good population.
Intermittent Shaking - Strangely enough, simply shaking the culture whenever you walk by it effectively increases the amount of yeast per volume of wort. Obviously, it depends how often you walk by, but the idea is to keep the yeast suspended as often as possible.
Stir Plate - Using a lab-type magnetic stir plate, you use a magnetic bar that spins in the wort and constantly keeps the yeast suspended. This greatly increases the cell count per volume, and can be found relatively cheaply on Ebay, or you can make your own.
The graph below gives you an idea of how many cells you might have using a simple 1-step starter, meaning you use say 2 Liters of wort, dump your package of yeast into it and do nothing else beyond the the above scenarios.
Essentially, if you shake the flask once in a while, you'll need around 4 liters of starter wort for our theoretical beer. If you use a stir plate, you only need 3 Liters or so. Not a huge difference, but wort ain't cheap either.
Now a way you can increase cell count given a certain volume of wort by increasing the cell density in the wort by chilling the yeast and decanting the used up wort after the yeast have eaten all the sugars (usually take a few days). These are called steps, and I've laid out the same specs below, using 1.75 Liters total at steps of 0.25L, decanting then adding 0.5L and growing, decanting all that and adding 1L and growing it up.
Instead of using 4 Liters through intermittent shaking, you only need 1.75L of starter wort if you use these steps. It might take a bit longer, if you include the overnight chills to decant the used wort, but you've essentially cut your wort in half. Using a stir plate essentially allows you to use less wort overall, so it's something to be considered. It also grows a lot faster as well.
Beyond using a hemocytometer and a microscope to actually do cell counts to confirm your growth, you can monitor your starter using a hydrometer. You'll likely see a final gravity around 1.010-1.015 once the yeast have gone through it.
Culturing Yeast
A good way to save money for brewing is to keep your yeast stored. There are 2 main ways to do this, either keeping frozen cultures or plating on agar plates or washing the yeast from your last batch of beer. Washing yeast is really easy, and if you have room in your fridge for a few mason jars, you can easily save $7 per brew, and immediately start with enough yeast without the need for a starter. You can get about 5-6 generations out of a pack of yeast, so if you do the math that's about 30 5 gallon batches per pack! I'll get into both of these techniques later...
