Starters for 2.5 Gallon Batches?

I saw in another thread someone suggest brewing 5 gallons of beer, splitting it into 2 batches of 2.5 gallons each and pitching a packet of yeast in each. I am accustomed to preparing a starter for every 5 gallon batch. Should I continue this practice with these smaller batchs? Or can I get away with pitching just one packet of yeast.

I anticipate OG being between 1.070 and 1.085.

Maybe as a general rule, is the need for a starter simply compensating for the alcohol level or does volume play a role as well?

I'd suggest using mrmalty.com or yeastcalc.com to calculate the amount of yeast you would need. I imagine for most brews around 5% you could just use one pack of yeast.

maltoftheearth said:

Maybe as a general rule, is the need for a starter simply compensating for the alcohol level or does volume play a role as well?

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Volume and OG play important parts in the calculation of the yeast pitching amount. Starters also proof the yeast if using liquid yeast but are not required or recommended for dry yeast.
You will need around 15g of dry yeast for 1.085 OG but could probably get away with one 11.5gm pack provided you rehydrate as per instructions. If you do not rehydrate you will lose up to 50% of the yeast and that will definitely result in under-pitching I suspect.

Age of the yeast matters as well. I do lots of smaller batches, and always run them through Mr Malty. One pack without a starter may be enough if you are using fresh yeast, but if it is two months old, you will need a starter for a 2.5 gallon batch.

Long story short, you are dealing with living organisms, so it's better to treat each batch individually rather than than looking for hard and fast rules.

I do 2.5gal batches and learned the hard way that you still should do a starter for liquid yeast. It isn't so much to get more yeast growth but more to make sure it is healthy. For most moderate gravity beers the amount of yeast in a liquid pack/tube is fine for a 2.5 gal batch so you just need a small starter like 1L.

Dry yeast? I just throw the whole sachet in there. Even if 50% do die you still have plenty of yeast. Never had any issues with dry.