1) Cold Pitching,
Why does it seem to work? In certain brewing forums there has
been much discussion related to cold pitching yeast into ale
worts. Basically, about a pint of yeast is harvested from the
primary of a brew batch and stored in a sealed container at
refrigerator temperatures (about 45F). At some later time (perhaps
as long as 1-2 months), that yeast is pitched directly from
the refrigerated container into a new batch of sweet wort @
70-75F. Based on my experience (and observations) this method
works quite well, and appears to reduce lag times (from 1.5
to 4 hours). Can you help us understand why the cold pitching
process works? Or have we just been lucky?
-Mike Zapolski
RESPONSE:
1. I have not seen any studies done using
this protocol. If I had to take a guess it would be centered
around the Trehalose content in the yeast cell. Trehalose seems
to be an all around stress related factor. Almost immediately
upon the cold storage of the yeast, trehalose begins to build
up to help the yeast to adapt to its new environment. Upon pitching
this stress factor assists the yeast to adapt to its new environment;
warmer temperature and higher osmotic pressure. If the pitching
yeast is allowed to warm up for any appreciable time before pitching
the carbohydrate reserve, trehalose being one of them will
be quickly used up as an energy source. The yeast would then
take a longer time adapting to its new environment in the wort
thus increasing the lag phase.
Something similar happens when using Active Dry Yeast. The
factory builds into each yeast cell an abundance of the stress
factor; trehalose. Our recommendations is to rehydrate the
yeast in warm water and pitch into the wort (or must) within
30 minutes, because the yeast will begin to metabolize its
carbohydrate reserve including trehalose immediately upon reactivation
and weaken the yeast if it is not in the presence of a new
supply of energy. It will have also used up the stress factor
that would have assisted it in adapting to the new osmotic
environment. I am sure that there is more to the explanation
than I have given.
Dr. Clayton Cone
2) Mid-Fermentation Nutrient
Additions - Are there any advantages, or disadvantages, that
may occur by adding yeast nutrients to a beer (or wine) after
fermentation has begun, but before the mid-point between the
OG & TG?
-Mike Zapolski
RESPONSE:
2. Yeast respond to a fresh source of nitrogen through
out its growth phase and early pert of the stationary. The
sugar transport systems have a very short life(2+ hours) and
enzymes involved need replenishing and a supply of nitrogen.
So an incremental feeding is ideal especially to minimize H2S
production. This is ideal and begins to be a factor as the
O.G increases. With well mashed wort a low gravity would probably
not benefit from this. A high gravity fermentation would definitely
benefit. There are other things involved in incremental feeding.
All the nutrients up front result in an increased growth of
yeast with a lower level of protein when it reaches the stationary
phase. Incremental feeding restricts the initial growth but
increases the yeast protein level. The higher protein level
in each cell increases the fermentation rate and protects the
cell against alcohol toxicity near the end of fermentation.
Again, this is only beneficial to a higher alcohol fermentation.
If you have the analysis of the wort available you can add
the exact amount of nutrient. You will need to work with the
nutrient supplier. Usually I begin with 1-2 pounds of the product
per 1000 gallons(0.5 -1.0 gram / gallon)of wort. That is a
safe range to start with. You can go up or down on the next
batch according to your evaluation of the current batch.
Dr. Clayton Cone
3) What are the differences between yeast nutrients, extracts,
hulls, and energizers? What does each product do to facilitate
fermentation? At what stage of the brewing process should they
be added to be most effective? Under what circumstances should
one use each of these products [what should the brewer look
for as an indicator], and what might be a typical amount added
to a 5 gallon batch? Is there a product that combines these
individual items into a single overall yeast "Superfood"?
-Mike Zapolski
RESPONSE:
3.Yeast nutrient is anything that the yeast needs
for a healthy growth and to stay alive during the stationary
phase; sugar, useable nitrogen (FAN), minerals, trace elements,
vitamins and oxygen. A well balanced nutrient like Fermaid
K will supply these requirements. Most all malt wort contains
a well balanced diet for low gravity fermentations. Sometimes
minerals like zinc and magnesium are on the short side. It
is when you move up to higher O.G and higher cereal adjuncts
addition that added well balanced nutrients need to be considered.
Extracts
are concentrated extractions of malted barley (malt extract)
or autolyzed yeast with out the cell wall. Malt extract,
as you get in a kit, makes a very good beer. Many of the useable
nitrogens are bound up by the Maillard reaction and are not
available to the yeast. Yeast extract contain most of the nutrients
that the growing yeast require. However you are limited in
the amount that you can use. Above a certain level, you may
begin to detect it in the flavor of the beer.
Yeast hulls are
my favorite. It is probably the best balanced source of nutrient
but can be used in a limited amount before you detect it in the
finished beer. Lallemand yeast hulls are cell walls loosely separated
from the cytoplasm of well autolyzed yeast. These cell walls
contain well digested protein that is high in available nitrogen.
It also contains lipids that are necessary for yeast growth and
protection against alcohol toxicity. Lipids are what you produce
when you add oxygen to the fermenting wort.
Diammonium phosphate
is an excellent, cheap source of available nitrogen for the
yeast. You have to evaluate it carefully for flavor and aroma
profile if you use it as a sole supplement.
Energizers is a
name that could include any or all of the above. Many distributors
have their own formula. Fermaid K is a well balance yeast nutrient
that was formulated based on many years of experience of yeast
production. There are two new products that have come onto the
market recently. They do not replace the need for Fermaid K but
augment it: GO-FERM is a product that is used in the rehydration
water (not in the wort or must) for Active Dry Beer and Wine
yeast. It maintains the vitality of the yeast through out the
entire fermentation. This becomes important in higher gravity
brews. Servomyces offers a biological source of zinc to the yeast.
The biological source seems to make it more available for the
yeast.
Dr. Clayton Cone
4) For a given ale yeast type, does controlling ale fermentation
temperature in the 60-68F range have a noticeable affect on
the resulting beer's flavor? If so, which ale yeast types are
most sensitive to fermentation temperature?
-Mike Zapolski
RESPONSE:
4. If all other factors are the same, you should
be able to tell the difference in fermenting ale at carefully
controlled variations in temperature. Variations in the malted
barley, mashing and pitching yeast from batch to batch can
mask any differences that you would have when comparing different
fermentation temperatures. Very high alcohol fermentations
where alcohol toxicity is involved, cooler temperature near
the end may be needed for full attenuation.
Dr. Clayton Cone
5) What factors (that the brewer might be able to control)
influences yeast attenuation? For example, if an ale yeast
has an optimum temperature range of 68-73, will holding the
primary temperature at 68F yield a better attenuation, than
at 73F?
-Mike Zapolski
RESPONSE:
5. Attenuation or the conversion rate of all the
fermentable sugars to alcohol (plus by-products) is directly
related to temperature. So the higher the temperature the faster
should be the attenuation.
Flocculating after attenuation is primarily controlled by
the yeast strain itself. However, excessive re-pitching and
acid washing is detrimental to the hydrophobicity (flocculation)
of the cell wall. Deficiencies in minerals such as calcium
adversely affect the flocculation properties of the yeast.
Dr. Clayton Cone
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