Calculating viability of dry yeast?

[Graeme]

Hi Guys,

I'm a big fan of Mr. Malty and how easy it is to calculate starter sizes for liquid yeast. However, tomorrow I am going to be using dry yeast, and It does not have a production date, only a best before. It is going to be a 30L batch and am eager to know whether or not I will need to pitch one or two packs. Is there a way around this on Mr. Malty, or alternatively another calculator that can work this out?

Thanks allot!

Graeme

[Befuddler]

Dry yeast won't really degrade over time as long as it's kept cool and dry. Unless your beer is high gravity, one pack will do it.

[Graeme]

Dry yeast won't really degrade over time as long as it's kept cool and dry. Unless your beer is high gravity, one pack will do it.

It is 30L of a 1.050 gravity and the best before date is 03/2014. Will one hydrated pack be enough? I would have thought I would need two

[Befuddler]

The only dry yeast I've got in the cupboard is US-05 but the instructions say one pack is good for 20-30 litres. I wouldn't consider 1.050 high gravity, so I'd just go with the single pack.

[Wolfy]

When it's stored at typical refrigeration temperatures, dry yeast only loses about 4% of it's viability per year - so the date it was manufactured is much less important than it is for liquid yeast - just put in a year or so before the best-before date and then trust MrMalty like you have been happy to so far.

[orlando]

What about carefully rehydrating (per instructions in the book Yeast, White & Zainasheff) then making a starter out of it? 1/2 litre should be enough as you probably don't need a lot more than you aready have.

[Wolfy]

When it's made and packaged, dry yeast is essentially force-fed all the nutrients it needs to kick-off a healthy fermentation.
If you pitch dry yeast into a starter - especially a small volume starter* - it can/will exhaust/expend those food-reserves in the starter and essentially be 'less ready' or 'less healthy' once that starter is pitched into your beer. Hence why it's generally recommended to simply directly pitch the correct volume of dry-yeast (rehydrate if you wish).


*1 pint or 1/2 L is generally considered too small - as per Chris White on some of the TBN podcasts.

[orlando]

When it's made and packaged, dry yeast is essentially force-fed all the nutrients it needs to kick-off a healthy fermentation.
If you pitch dry yeast into a starter - especially a small volume starter* - it can/will exhaust/expend those food-reserves in the starter and essentially be 'less ready' or 'less healthy' once that starter is pitched into your beer. Hence why it's generally recommended to simply directly pitch the correct volume of dry-yeast (rehydrate if you wish).


*1 pint or 1/2 L is generally considered too small - as per Chris White on some of the TBN podcasts.

The reason I said 1/2 litre was because of issues surrounding over pitching. I read his comments about how small starters do not help to increase by much the number of yeast cells available for the wort. Given that the OP already has close to the right amount I thought this method would give him the amount he needed whilst avoiding the damage to the dried yeast if no rehydration was used.

[Wolfy]

It's not that the small starter size does not increase the number of cells - but rather that the small volume can actually hurt the yeast's vitality/health by not supplying enough nutrients for them to be happy and healthy.
The 'Yeast' book is (the way I read it anyway) fairly clear in suggesting that starters really should be focused on creating healthy yeast as it is about increasing yeast cell numbers (which is the purpose that most home-brewers usually think of a starter for).

[darkonnis]

I read it the same, it does say in one section that it is better to have fewer young healthy cells over lots of weak cells.
You could of course throw some yeast nutrient in the starter but would you see better results? Likely no. Better to just pitch or rehydrate and then pitch. Depending on your prefered method.
I've rehydrated my packs lately and I don't see much in it between a hydrated pitch and a straight pitch, activity level is about the same usually and so far *touch wood* I haven't had any stuck ferments, I don't need to rouse it or anything, straight in, away it goes. My last US-05 pack (hydrated) did 27L & 1.045 in a few days, infact I'm certain it was done in 3, but i left it an extra 6 days or so to sort itself out and to dry hop. OP should be fine to just put it in, 1.050 isn't really high grav.

[gregorach]

The issue is primarily one of the depletion of reserve carbohydrates (glycogen and trehalose). The yeast will use up these stores as they begin to metabolise in preparation for reproduction, but then suddenly run out of food (due to the limited availability in the small starter volume), leaving them unable to rebuild their reserves before you pitch them into the full volume. Supplying additional yeast nutrients will not address the problem. To use an analogy, you're waking the yeast up early, but then not giving them enough breakfast.