I am brewing 5 gallon batches. I end up with 5.5 gallons after the boil so I split the batch evenly into two(2) Corney kegs fitted with an air lock on each gas in. I ferment in the two kegs and then use CO2 to transfer from the primaries into a single CO2 filled secondary (or simply into the serving keg). What I need to know is should I split the yeast between the two primaries or should I pitch one packet of yeast per primary?

  • You don't need to split the batch if you use a spunding valve. In fact, depending on the valve setting, you won't need to carbonate either.
    – Wyrmwood
    Nov 19, 2013 at 20:05
  • The spunding valve looks interesting and at the same time complicated. I'm going to concentrate on one complication at a time but I will look into that later. Nov 19, 2013 at 20:54

3 Answers 3


In short: use the same amount of yeast.

You should use the correct amount of yeast for 5 gallons, either split between the two cornies or added to the batch before you split it. Dry yeast packets have (more than) enough cells for a 5 gallon batch. Liquid yeast smack packs generally do not have enough cells for 5 gallons of wort, which is why starters are important.

  • 1
    and be sure to rehydrate! ;)
    – mdma
    Nov 18, 2013 at 21:20
  • Thank you. As it turns out, I was unaware of the insufficiency of the 'slap pack'. I've used them for years for five gallon kit beers and it never occurred to me why it was taking more time than advertised to start fermenting. I have ordered some equipment and will begin making starters from here on out. Nov 19, 2013 at 20:59
  • yeastcalc.com is a great resource, as is the brewersfriend.com link mentioned on your original question and the "gran-daddy" mrmalty.com site as well. The two most important improvements to process most brewers can make are yeast health/pitch rate and fermentation temperature control.
    – jsled
    Nov 20, 2013 at 2:44


If you don't have time to make a yeast starter then just split it between the two.

But you should look into making yeast starters. I started out using 1 gallon glass jar and shaking it. You need to make larger started but DME is cheap. If and when you get a stir plate started will be much smaller.

Extra step will pay for its self if you start making oversize starters and splitting them. Saving one for later brew day.


To be perfectly honest, you should probably be taking the normal amount you use for a 5 gallon batch and making a yeast starter anyway (even without the splitting). Shake up the starter when you are ready to pitch the yeast to get the cells evenly distributed and then split that into two.

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