# How much yeast to use in a 1 gallon brew?

Discussion in 'Beginners Brewing Forum' started by Jonny the Brewer, Jun 5, 2020.

1. ### Jonny the Brewer Member

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#1
Hi guys.

I'm a bit confused. In the one gallon brew I am doing tomorrow I'm using a sachet of US 05 yeast. Now, it says on it that the sachet is 11.5g and it's to be added to 20-30 litres of wort. I like a strong ABV so I'll calculate it as per 20 litres.

A few sums - 20 / 11.5 = 0.575g of yeast per litre. There is 4.55 litre in a gallon, so 0.575g x 4.55 = about 2.62g of yeast I will need to pitch into my one gallon of wort.

However I was reading something yesterday that said to use a third of the sachet per gallon. Is this correct? Yeast is tricky stuff so my question is - Do you work it out by dividing it like I've done, or is it not as simple as that?

Any help appreciated as I worry I've got a couple of beers fermenting from last weekend and the weekend before that that have too little yeast and will be very low ABV. Thanks all!

Jonny

2. ### BrewPatgonia Well-Known Member

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#2
your calculation works. I always calculate and measure my yeast on a gram scale.
the package is a typical 11.5 gms. The manufacturer recommends 50 to 80 gms per hectoliter, therefore, .5 - .8 gms per liter.
if you use a third of the package, it gives some additional insurance for a decent fermentation, but if the yeast is fresh.. 2 gms per gallon is good enough. if the ABV is above 7%, then I would be more comfortable with a higher pitch rate... 1/3 of the package for 1 gallon.

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3. ### Nosybear Well-Known Member

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#3
Flipside: While you can overpitch, it's hard to do so and its effects are not as severe as underpitching. Me, I'd guesstimate a half-sachet and call it good.

4. ### Bubba Wade Well-Known Member

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#4
I make 2.5 gallon batches. Some of the time, I drop a whole 11g packet in the fermenter, but other times, I pitch approximately half the packet and tape the other half up for later use. I have been using the half packet method more and more as it seems that yeast is one of my more expensive ingredients.

I have made the same beers with both the full and half packet, and I have noticed no discernible differences in taste or fermentation time.

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5. ### Frankenbrewer Well-Known Member

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#5
Hey BWade, I have a half packed of S-04 from last year. Do you think it is still good? It is double taped and in a ziplock bag in the frige.

6. ### Jonny the Brewer Member

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#6
Great advice guys thanks. I didn't realise it was ok to chuck in a half packet! I might just do that from now on.

Last weekend's brew stopped bubbling completely after 4 days... I think I might have under-pitched it. Do you think I could add more yeast to it now, a week later?

7. ### Nosybear Well-Known Member

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#7
No. The yeast likely used up all the sugars. Take a gravity reading, if possible, and I'll bet you're near your final gravity.

8. ### BrewPatgonia Well-Known Member

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#8
to Franken, I think you would be OK with the -04 a year old, but better to make a starter with it to be sure. I am using some -05 which I purchased 2 years ago... (I purchase 500 gm packs)... and using a starter with dry yeast isn't necessarily normal..but it is my way to verify activity as well as grow more cells. with 2 yr old yeast... I am getting good activity 70 percent of the time. I store mine in vacuum packed packaging..near 33 deg F. Not a normal situation, but I couldn't use what I had purchased due to work assignments.

to jonny, mirroring what 'nosy' stated; you should be fine without pitching more yeast; most likely fermentation is complete. if you cannot verify with sg readings, it is better to wait a week at least, to let the active yeast clean up... prior to bottling, etc.. only positive results can occur with reasonable patience.

9. ### Bubba Wade Well-Known Member

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#9
Most likely. But as stated previously, making a starter is a pretty good idea if itâ€™s that old. I try to use my half packets within two or three months. But the dry yeast is pretty hardy. It will likely work without a starter given how you stored it.

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10. ### Jonny the Brewer Member

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#10
Even if I didn't pitch enough?

Is it possible to add not-enough yeast, and still have it eat all the sugar? Yeast is very confusing!

And how would I know when I'm at FG? For me I just take an OG and an FG and work out the ABV - I wouldn't know how to aim for an ABV.

I am guessing the two factors are the sugar (grain) and the yeast... varying the types and quantities of each make variations in ABV?

11. ### Bubba Wade Well-Known Member

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