Making a Yeast Starter for your Home Brew Beer

by Brad Smith on April 1, 2008 · 62 comments

The quality of your homebrew can be dramatically improved by making a yeast starter. Home brewers often toss a packet or vial of yeast into their beer without much thought to the quantity needed. Though modern liquid brewer’s yeast smack packs and vials are a huge improvement over older dry yeast packs, these packages do not contain enough yeast cells for optimal pitching. Underpitching results in slower startup, higher risk of infection, off flavors and sometimes incomplete fermentation.

How Much Yeast is Enough?

In general, lagers require a larger starter than ales. George Fix’s book “An Analysis of Brewing Techniques” recommends pitching rates of 0.75 mllion cells an ale and 1.5 million cells for lager. The number is measures in million of cells per milliliter per degree plato.

Converting to homebrew units, his ale figure translates to 4 billion cells per point of original gravity per 5 gallon batch (1.048 original gravity would be 48 points or 192 billion cells). For a 5 gallon homebrew, lets use the figure of 192 billion cells.

An average White Labs yeast vial contains around 100 billion cells of active yeast. Therefore without a starter, you would need two yeast vials to reach optimal pitching for our 5 gallon example. The large Wyeast activator packs contain around 100 billion cells as well, so again you would need two packs. The smaller smack packs contain only 15-18 billion active cells, so you would need 11 for the same 5 gallon batch. (Ref: MrMalty). Keep in mind you would need to double the above figures for a lager.

Fortunately, creating a starter is an excellent alternative to purchasing large quantities of yeast. Research varies, but a starter of 1 liter will yield approx 150 billion cells and a two liter starter will yield from 200-240 billion cells. So a 1.5-2 liter starter is sufficient for an average 5 gallon batch. For a 10 gallon batch, a 4 liter starter is appropriate (up to 400 billion cells yielded) but may require a two step starter (first a 1 liter starter, then transfer it to a 4 liter starter) if you are pitching less than 100 billion cells initially. (Ref: AHA Tech talk, 8/31/05)

Making the Starter

Creating a starter is very easy. You want to start 18-24 hours before your brewing session, so the yeast can reach an active state before pitching. If you are doing a two stage starter, allow 18-24 hours for each stage. I use a large pyrex flask, but a very clean pot is a suitable substitute of you can cool it quickly. Dry malt extract is easy to store and use in small quantities. To determine the amount to add, you can create a mini-recipe in BeerSmith that is the size of your starter and adjust for a target gravity of around 1.040. Alternately, use this rule of thumb: between 3.5 and 4 ounces of extract per liter (or quart) will give you a good starter.

Dissolve the dry malt extract, boil it for 10-15 minutes to make sure it is sterile, and then cool it quickly in an ice bath and transfer it to a sanitized container. Once it reaches room temperature, pitch your yeast and seal the container with an airlock to prevent contamination.

Allow the starter to ferment between 18 and 24 hours. Pitch the entire contents of the starter into your batch of beer to get an active, robust start. Pitching yeast at the proper rate will significantly reduce the lag before active fermentation begins, promote complete fermentation, reduce the risk of infection and improve the overall quality of your beer.

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{ 8 comments… read them below or add one }

Bren December 10, 2013 at 3:11 am

Greetings Brad:
Not sure this thread is active anymore but I have an important question nonetheless. Perhaps I missed this question already, and forgive me if I did. Say I have a 5 gallon RIS batch that is supposed to finish around 13% after a 6-8 mo. fermentation with WLP090. The initial starter was 1.5 liters and pulls the RIS to 9%, therefore I have 4% left until the desired .01 is reached. Say I want to pitch K1-V1116 for my secondary fermentation: Is the rule of 1.0-2 liters per 5 gallon batch still viable in this scenario? Thanks


Anders Aqulin December 24, 2013 at 8:33 pm

Hi Brad,
when using the Starter tab in BeerSmith 2, I don’t understand how much malt extract I should add. I only see the starter volume per se, but not the volume of malt extract to add.

Can you please advise!

Kind regards

Kevin March 25, 2014 at 2:41 pm

Just one note – your starter should not have an airlock since it needs an abundance of oxygen to propagate. The standard practice is to cover your flask with aluminum foil and that should be enough to keep unwanted bacteria out and allow oxygen to get in.

Tim July 24, 2014 at 4:35 pm

Brad, What do you think about doing an all-grain 4 liter starter, but only using 1 liter for the first stage, while storing the other 3 liters in the fridge till 24 hours later, then reboiling the 3 liters, cooling and adding to the 1 liter starter? My main question has to do with storing the extra wort (3 liters) in the fridge for a day to pitch the next night.

Thank you,


Fred Floer September 11, 2014 at 8:30 pm

I brew full grain, getting 6 gal out of mashing and boil it for 5 gal. beer. Will a starter, and I need 2ltr., spoil my brew by diluting ?

John Hooper November 24, 2014 at 7:38 pm

The instructions above omits the need to oxygenate teh wort before pitching the yeast. Slight over site but necessary.


Johnny Lager April 23, 2015 at 5:46 pm

Could someone explain how to wash and reuse yeast?

Dennis Chartier May 21, 2015 at 10:11 am

It is my understanding that to make a yeast starter with a stir plate you would combine half cup of DME with 2 pints of water. Boil for 10 – 15 minutes, cool below 80 degrees F and pitch a veil of White Labs yeast which the specific gravity would be approximately 1.040. My question is that if yeast multiplies in a starter up to five time the number of cells, will the basic starter ingredients listed above result in a cell count close to 500 Billion if the veil is new and contains 100 Billion.

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