[newpotat]

I am a relatively new homebrewer.  Up until now I have always made 5 gallon batches.  I was thinking of brewing a few 2 1/2 gallon batches of some simple beers (American Pale Ale or American Brown Ale) and was wondering if I should adjust the amount of yeast that I use.  Any tips would be appreciated.  Thanks.

[stevedorau]

Take a look a MrMalty.com.  JZ's site is the best yeast calculator. Based on his tests.

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[stevedorau]

One of the biggest factors is the age of the yeast. Viability changes significantly in months.

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[dmtaylor]

A lot of great advice has been shared already!  I'll just go overboard here like I always do.... 

Definitely use MrMalty.com if you aren't sure.  This calculator is easy to use, and you are certain to have enough yeast with it.  Personally I find that it is overly conservative and you can get away with a little less than it says.  But it's not wrong to just go with their recommendation if you want to play it safe.

That all being said, I will also tell you that the calculator is certainly more accurate for liquid yeast.  For dry yeast, you really don't need to use that calculator at all, the reasons being...

Dry yeast is extremely stable and resilient and reliable.  If you store in the refrigerator, it will maintain >50% viability for many many YEARS, maybe 5 years or more.  Another advantage is that dry yeast does not really need to be rehydrated.  It is true that about 50% of the yeast will die if you don't rehydrate.  However, it is also true that a typical dry yeast packet contains at least twice as much viable yeast as a liquid pack.  These two factors tend to cancel out one another for most ales (i.e., 50% x 200% = 1).  So, for a standard gravity ale, an unhydrated pack is good for at least 5 or 6 gallons, maybe more, and a rehydrated pack is good for at least 10 gallons.  With lagers or cold fermented ales, you do want to use extra yeast since it's more sluggish at cold temps, so in cases like that, you might want to rehydrate or use extra, maybe.

Splitting packs of dry yeast is super easy.  Sanitize your hands, the packet, and scissors, cut it open, use the amount you think you need, fold over the corner and tape it shut, and put back into the refrigerator.  It's that simple.

For liquid yeast, you either need some of the old Wyeast vials to hold the extra, or some sanitized mason jars or something like that.  Liquid yeast will only keep in the fridge for approximately 9 months on average (plus or minus, depending on many factors), and with liquid yeast, you really should always use a starter, regardless of what MrMalty says.  For small batches, it's easier to justify skipping the starter, but it's still always the best idea to do one anyway, even if it's only in a cup or two of wort, just to wake up the yeast better.

Hope this helps.

[cdawson]

Splitting packs of dry yeast is super easy.  Sanitize your hands, the packet, and scissors, cut it open, use the amount you think you need, fold over the corner and tape it shut, and put back into the refrigerator.  It's that simple.

+1 - I have brewed a couple of small batches myself using this method and did not have any issues with either the amount of yeast used or the viability of the yeast on the second batch a month or so later using what was left in a packet of US-05. For the first batch I simply pitched approximately 1/2 of the packet. 

[dmtaylor]

Splitting packs of dry yeast is super easy.  Sanitize your hands, the packet, and scissors, cut it open, use the amount you think you need, fold over the corner and tape it shut, and put back into the refrigerator.  It's that simple.

+1 - I have brewed a couple of small batches myself using this method and did not have any issues with either the amount of yeast used or the viability of the yeast on the second batch a month or so later using what was left in a packet of US-05. For the first batch I simply pitched approximately 1/2 of the packet.

Yep.  And I should add: There's no need to weigh the amount to the exact gram or anything either.  Approximation is usually good enough.  Those dry yeast cells are so geared up and ready to eat sugar, they don't much care about population density, they'll just jump right in there and start eating.  An exception perhaps is BRY-97, which is a little more sluggish than other dry yeasts, but still a great performer after the first 24-36 hours of wake-up time.

[JJeffers09]

To expand on everything dmtaylor says you need to consider the pichrate for the style, the OG/P/Brix, and your fermentation temp.  Yeast is no less complicated that mashing.  It has as many, if not more, variables than a mash will.

Dry yeast can be easily measured in grams, used accordingly and lasts forever.  Rehydration should only be done if you need more viable yeast than you have on hand, in which case you're making a starter.

Liquid yeast is as pointed out about viability, stored conditions, strain, and metabolized oxygen, etc.  It is always good practice to make a starter and pitch the amount desired in mL of slurry.

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[stevedorau]

I am of the opinion that you want to introduce as a little dead or dying yeast as possible in a beer. Dying yeast express chemicals that can contribute to off flavors. I have never seen an experiment on this and it is probably worth trying. Rehydration is fairly easy and it would seem like it's worth the investment to make the best beer possible.

[dmtaylor]

I am of the opinion that you want to introduce as a little dead or dying yeast as possible in a beer. Dying yeast express chemicals...

Personally I refer to dead yeast as "yeast nutrients".  At least while it's still fermenting.  In the bottle or keg after many months, I would agree, a lot of dead yeast in the package would be a very bad thing.  Fortunately most of them settle out during fermentation and fortunately most of us take measures to keep all that junk out of the beer at packaging.

I see your point though too.  Cheers.

[Steve Ruch]

Maybe I'm just lazy, but I brew mostly three gallon batches and just round up to the nearest whole package when I pitch dry yeast. I also use Munton's (6 grams) on a lot of my British ales.

[Steve Ruch]

The dry yeast packages that I have used have all be 11.0 grams or 11.5 gram.  When you say "nearest whole package", are your packages typically 6 grams?

Most of the ones I use are 11 or 11.5 and if a recipe calls for less I just throw the whole thing in. Munton's comes in the smaller size and I like it for British ales which mostly call for four or five grams.

[Mythguided Brewing]

I almost always brew 1.0 gal batches, just because I like to experiment a lot.  Just for grins, I once split a 1 gal batch into two 1/2 gal jugs - pitched one with 1/4 packet dry yeast, the other with the remaining 3/4 packet (Mangrove Jack's West Coast Ale M-44).  Absolutely no difference in FG/attenuation between the two.

[case thrower]

I also brew 2.5 gallon batches and I use only dry yeast.  I almost always rehydrate and for ales I use the amount of grain to determine how much yeast to use.  One gram of yeast for each full pound of grain.  I'm just starting to do lagers and for lagers I use the whole packet.