There are several choices for reducing costs with your yeast.  You can reuse the yeast cake, harvest your yeast, create multiple starters from a single liquid yeast pack, or use dry yeast.  Each of these choices can save you money, but there are also trade-offs.  Here are a few things to consider with each method.

Pitch your wort on your yeast cake

The first option is to rack your second beer on top of your yeast cake.  The idea is once your first beer has completely fermented; rack the beer leaving just the yeast behind.  Then pour your second beer over the yeast.  It’s like adding a very large starter to your wort.

The fermentation should go quicker the second time around.  You do need to be careful with this method because you are over pitching.  Autolysis (when the yeast cells die and degrade) usually happens when you leave your wort on the yeast too long (months), but it can happen much quicker when you over pitch.

Autolysis happens much quicker when you over pitch because your yeast is skipping over the aerobic phase of the yeast life cycle.  Fewer new cells are created and your fermentation will not be optimal.  You are creating a retirement community of yeast cells.  The yeast will not be as healthy and will die sooner.  Too much dead yeast creates a really nasty off flavor in your beer.

With that said I’ve added new wort onto yeast cakes and produced good beer.  Of course I did this a while ago before learning more about how yeast works, but you can do it.  In fact I didn’t come up with the idea myself; I heard it from another brewer (who probably heard it from someone else too).  Many home brewers add new wort onto their yeast cakes.  It saves you money, but it is risky.

• If you pitch on your yeast cake you are overpitching, which can lead to autolysis
• I’ve done it and it went fine

Become a yeast farmer and harvest your yeast

A better alternative is to properly harvest your yeast.  You should always harvest from the fermenter with the fewest generations.  If you are harvesting yeast for the first time this is not an issue, however, if you are continually harvesting you want the youngest yeast.

You also do not want to harvest yeast from beers with alcohol contents over 6.5% ABV.  The higher alcohol brews will stress your yeast.  These changes can have negative effects on future generations (darn you evolution), and produce off flavors in your beers.  It’s a good practice to use the yeast on similar beers, or go from light beers to dark beers.

Harvest your yeast after you have racked your beer from your fermenter.  Swirl the remaining liquid and yeast slurry.  Collect some of the slurry in a sanitized jar about half way.  If you are collecting your yeast from a conical fermenter, try to get the yeast in the middle.  The yeast at the bottom is likely to be dead yeast and trub (stuff that isn’t beer, water or yeast). You’ll get better quality yeast from the middle.

Then fill the rest with cold boiled water.  You want to boil the water you add and then cool it back to room temperature because you want to add sterilized water with no oxygen.  Boiling water lowers the amount of oxygen in solution, that’s why it’s important to shake your carboy before pitching your yeast.  In this case, the oxygen will cause the yeast to use up their glycogen reserves (energy reserve carbohydrate).

Let your jar of water and yeast sit for a few minutes.  During this time the trub should settle to the bottom.  Pour out the top part of the yeast solution into another sanitized jar leaving the trub.  Repeat this process until your yeast has a very light golden color, and very little trub is left at the bottom of the jar.

Close the jar and save your yeast in your refrigerator.  Do not keep the yeast for more than a few days (5 days max).  The sooner you use your harvested yeast, the better.  If it turns dark brown, discard the yeast.  When it’s brown, the yeast died.  If you open the jar, the yeast will smell awful.

Before you use your yeast, make sure it smells like yeast.  Smelling the yeast before using it is your best defense against ruining your beer with infected yeast.  If you pitch infected/bad yeast your beer will be ruined.

Wyeast recommends you pitch slightly more yeast, than you would from a first generation laboratory culture.  They state “the [harvested] culture can be void of sterols, enzymes, and glycogen, as well having possible poor cell membrane health”.

If you are not brewing beer once a week, you probably do not want to use the above two methods.  There is real risk of contamination, and you could ruin a few batches.  You have been warned.  Still there are other ways to save money on your yeast.

• Yeast harvesting is good if you frequently make beer
• If you pitch bad harvested yeast, your beer will be bad
• Keep your yeast cold and use your harvested yeast within 5 days
• Don’t harvest your beer from high alcohol brews

Create more starters from smaller batch

I usually brew at least 10 gallons of beer at a time, sometimes more.  My reasoning is the brewing process is just as difficult making 5 gallons as it is making 20 gallons.  The problem is you will need several vials or smack packs of liquid yeast.  This gets expensive quick.  At $8 a vial, I would be spending $32 on yeast alone.

If you create multiple starters, you can make your one vial go a long way.  I’ve created several starters a few days before my brew day.  I just pour half of the yeast into each starter.  I’ll grow the yeast up until I have the correct amount of yeast for the size of the wort I am planning to brew.  This gives me the yeast I need for a healthy fermentation, but I only have to buy one vial of yeast.  The best part is it safer than the first two options.

• With a starter you will need fewer vials of yeast, but you can still pitch the proper amount
• Safer than harvesting yeast

Dry yeast is not your granddaddy’s yeast

You’ve heard the saying you get what you pay for.  This used to be true for dry yeast, but yeast manufacturers are getting much better at producing quality yeast.  In the past your dry yeast choices were ale or lager, and the yeast was susceptible to infection.  While dry yeasts still do not have the wide variety liquid yeasts have, the yeast quality is getting better.  The best part is dry yeast is significantly cheaper than liquid yeast.  You also might not need to create a starter, depending on the starting gravity of your beer.

There are also other benefits with dry yeast.  A dry yeast sachet can last up to two years in your refrigerator.  This makes buying in bulk another option for saving money, and you will always have yeast on hand.  A liquid yeast pack will last only for a few months.

If you are creating a beer where you do not need a specific strain of yeast, dry yeast is a good option.  The dry yeasts produce great results, especially if you want a neutral or absent yeast profile in your beer.  If you are looking for a specific flavor from your yeast, you’re still better off with liquid yeast.

Do not reuse the yeast from a dry yeast package.  According to Danstar, you can repitch the yeast slurry like any other yeast (up to 5 generations), but they suggest verifying the cleanliness of the yeast first with equipment which would not normally be available to the homebrewer.  This comment might be directed at professional breweries.  Fermentis does not recommend reusing the yeast since the risk of infection outweighs the cost of new yeast.  Since dry yeast is so cheap, I wouldn’t bother reusing the yeast.

• There are more dry yeast strains available, but not the number liquid yeast enjoys
• It may not be worth reusing, since it is easy to just buy another pack
• You can store dry yeast for up to two years