Why double the yeast for a heavier beer?

[Joerg]

One of the beers planned for late November is a Scottish Heavy. It ain't
very heavy for my taste, only around 6% but the supplier of the kit
recommends using two 11.5g S-04 yeast packages for a 5-gallon batch
instead of just one. Why is that?

I always aerate by racking off from the brew kettle into the fermenter
and letting it splash the whole time. I notched a 3/4" irrigation pipe
tee as an angled holder for good splashing even when unattended for a
while. By the end there is an impressive foam layer of 2-3 inches on top
of the transferred wort. Ought to be enough oxygen, methinks. Since
yeast makes babies all the time, why use more than one yeast pack?

AFAIK dry yeast doesn't require much aeration but if a wort is well
aerated does the innoculation quantity really matter?

When I harvest yeast it's the whole trub and usually I take no more than
20-25% of the trub from a previous batch to ferment the next. It always
works and ferments all the way down to the range around 1.012 FG. Then I
use 20-25% of that new trub again for a 3rd batch and it also works.
Lots of yeast babies must be in there.

[baloonon]

Post by Joerg
One of the beers planned for late November is a Scottish Heavy.
It ain't very heavy for my taste, only around 6% but the supplier
of the kit recommends using two 11.5g S-04 yeast packages for a
5-gallon batch
instead of just one. Why is that?
AFAIK dry yeast doesn't require much aeration but if a wort is well
aerated does the innoculation quantity really matter?

Dry yeast still requires oxygen. There's inevitably some getting in when
you transfer to the fermenter, but adding oxygen will help faster
growth.

For really big beers, you want to add more yeast to speed up the start
of strong fermentation. The production of alcohol and the drop in pH
helps chase off rival microorganisms, and more yeast generally means
faster fermentation.

There's also the issue of the flavors and aromas yeast can produce
depending on how much is pitched at the beginning. Usually people want
the cleaner or more predictable result of pitching a lot of yeast, but
sometimes brewers look for the funkier results you can get from some
yeasts if they are underpitched.

A lot of Scottish beers were brewed at lower temperatures in the past,
so if that's the case with your recipe, pitching a lot of yeast may be a
way to compensate for slower growth at lower temperatures. So in this
case, it may be that the recipe is trying to compensate, in the same way
you generally pitch two packets for lagers.

In general, though, one packet is enough for a 6% ale brewed in the 60s
Farenheit.

[Joerg]

Post by baloonon

Post by Joerg
One of the beers planned for late November is a Scottish Heavy.
It ain't very heavy for my taste, only around 6% but the supplier
of the kit recommends using two 11.5g S-04 yeast packages for a
5-gallon batch
instead of just one. Why is that?
AFAIK dry yeast doesn't require much aeration but if a wort is well
aerated does the innoculation quantity really matter?

Dry yeast still requires oxygen. There's inevitably some getting in when
you transfer to the fermenter, but adding oxygen will help faster
growth.

I always let it splash a lot regardless of whether using dry yeast or
harvested yeast with trub. When racking off from the kettle I make sure
the hose holder gets placed into at least three positions on the rim of
the fermenter bucket to make sure the splashing is somewhat uniform.

Post by baloonon
For really big beers, you want to add more yeast to speed up the start
of strong fermentation. The production of alcohol and the drop in pH
helps chase off rival microorganisms, and more yeast generally means
faster fermentation.
There's also the issue of the flavors and aromas yeast can produce
depending on how much is pitched at the beginning. Usually people want
the cleaner or more predictable result of pitching a lot of yeast, but
sometimes brewers look for the funkier results you can get from some
yeasts if they are underpitched.

Aha! That makes sense, thanks. Didn't know that, I learn something new
every day.

Post by baloonon
A lot of Scottish beers were brewed at lower temperatures in the past,
so if that's the case with your recipe, pitching a lot of yeast may be a
way to compensate for slower growth at lower temperatures. So in this
case, it may be that the recipe is trying to compensate, in the same way
you generally pitch two packets for lagers.
In general, though, one packet is enough for a 6% ale brewed in the 60s
Farenheit.

For S-04 yeast Fermentis recommends 59-68F, the usual. I rigged up a
cooler/heater chamber where I can dial that in and change temps as the
fermentation progresses if needed. The temp even gets radio'ed into the
living room just to keep an eye on it and make sure all things are well
down there.

[baloonon]

Post by Joerg

Post by baloonon

Post by Joerg
One of the beers planned for late November is a Scottish Heavy.
It ain't very heavy for my taste, only around 6% but the supplier
of the kit recommends using two 11.5g S-04 yeast packages for a
5-gallon batch
instead of just one. Why is that?
AFAIK dry yeast doesn't require much aeration but if a wort is well
aerated does the innoculation quantity really matter?

Dry yeast still requires oxygen. There's inevitably some getting
in when you transfer to the fermenter, but adding oxygen will
help faster growth.

I always let it splash a lot regardless of whether using dry yeast or
harvested yeast with trub. When racking off from the kettle I make
sure the hose holder gets placed into at least three positions on the
rim of the fermenter bucket to make sure the splashing is somewhat
uniform.

Supposedly for big beers (I'm thinking over .08 or more, I'm too lazy to
look it up) it is recommended to disperse pure O2 into the solution
because no amount of splashing will get the levels high enough.

On the other hand, this experiment suggests that the value of
oxygenating is limited:

<http://brulosophy.com/2015/10/19/wort-aeration-pt-3-nothing-vs-pure-
oxygen-exbeeriment-results/>

It compared two halves of a split batch of 1.096 beer, one half in a
fermenter with nothing done to add oxygen and the other half in a
fermenter dosed for three minutes with pure O2.

A blind taste test didn't come up with a significant number of testers
who could tell a difference between the two, although the brewer thought
he could notice a slight difference in flavor and aroma and slightly
preferred the oxygenated batch. Also, the oxygenated batch fermented
faster and finished slightly lower in gravity.

I'm sure you need to take this as just one data point, and the results
may vary more depending on gravity, yeast strain, fermentation temp, and
other variables. And presumably the difference may be smaller between
batches when adding pure oxygen and adding some oxygen by splashing and
mixing while the fermenter is filled.

But it suggests oxygenation is one of those things that is good to do
but not critical to the results, maybe along the lines of fermenting a
degree or two higher than the recommended temp for a lot of recipes --
something that is usually (maybe not always) only a small deal.