FERMENTATION 101

I thought it would be interesting to run through the fermentation
process and try to describe a little bit more clearly what is
actually taking place when you are producing a fermentation.

It is not necessary to understand all the ins and outs of a
fermentation to make wine--particularly if you are following a
good recipe with solid directions. But none the less, having a
more intimate understanding of the fermentation process can only
make you a more accomplished winemaker if nothing else.


- What Is Really Going On

In very general terms a wine fermentation occurs when yeast
consumes sugar and converts it into approximately half alcohol
and half CO2 gas (carbonation) by weight.

For example, if you had five gallons of juice that had 10 pounds
worth of sugar in it, and you fermented all of that sugar with
yeast, you would end up with 5 gallons of juice that has roughly
5 pounds of alcohol in it.

The other five pounds of sugar would dissipate into the air as
CO2 (carbonic) gas. So in fact the five gallon batch would become
five pounds lighter than it was before the fermentation started.

Realize that the breakdown of alcohol verses gas would not be
exactly half and half, but usually it would be very close. Some
variances do occur depending on external factors such as the amount
of available air, nutrients as well as the type of yeast used.
But, rest assured that it would be within 46% one way or another.

It is important to note here that the 10 pounds of sugar that was
in the five gallon batch may not have come all from sugar you
added, but partially from the fruit as well. And in some cases,
such as when making a wine from grapes, there may be no sugar
required at all. In these cases enough sugar is already in the
fruit itself to produce a wine with 11 or 12 percent alcohol.


- Fermentation Stages

A wine fermentation has two distinct stages: primary and
secondary--also sometimes described as aerobic and anaerobic
fermentations.


* The Primary Fermentation will typically last for the first four
to seven days. On average, 70 percent of the fermentation
activity will occur during these first few days. And in most
cases, you will notice considerable foaming during this time of
rapid fermentation.

The primary fermentation is also called an aerobic fermentation
because the fermentation vessel is allowed to be opened to the
air. This air plays an important roll in the multiplication of
the yeast cells.

Here's how important. The little packets of yeast that is
generally called for in a five gallon wine recipe will typically
be multiplied up to 100 to 200 times during the few days of
primary/aerobic fermentation. Without air this multiplying stage
is hindered. That is why it is important that you do not use an
air-lock during the first few days of a fermentation and allow
the fermentation to be open to air.

Alcohol is being produced during the primary fermentation as
well, but a significant portion of the yeast's energy is being
devoted to reproducing itself.


* The Secondary Fermentation is when the remaining 30 percent of
of fermentation activity will occur. Unlike the typical four to
seven days the primary fermentation takes, the secondary
fermentation will usually last anywhere from two to three weeks
depending on the amount of nutrient and sugars still available.

So as you can start to see, the secondary fermentation is much
slower with less activity at any given time. You will also notice
the activity becoming slower and slower with each passing day.

The secondary fermentation is an anaerobic fermentation which
means that air exposure is to be kept to a minimum. This can
easily be done by attaching an air-lock to the fermentation
vessel.

It is this reduction in air exposure during the secondary
fermentation that entices the yeast to forget about multiplying
and start giving its energy completely to making alcohol.


- Fermentation Considerations

* Temperature plays an extremely vital role in the fermentation
process. If the fermentation temperature is too cool, the yeast
may not be invigorated enough to ferment. It will simply remain
in the juice, dormant.

If the fermentation temperature is too warm, the yeast may
ferment fine, but the flavor of the wine will usually suffer.
This is because of the increased production of unwanted enzymes
by the yeast and the possible growth of micro-organisms that
thrive in warmer temperatures.

The optimum temperature for a fermentation is 72 degrees, but
anywhere between 70 and 75 will do fine.


* Throughout the fermentation process you will need to transfer
the wine off the sediment into a clean container. This is a
process that is referred to as "racking" in most wine making books.

This should be done at the end of the primary fermentation or
when the Specific Gravity reading on your hydrometer reaches
approximately 1.030. It should also be racked after the secondary
fermentation as well a right before bottling the wine.


* It is also important to understand that once the wine's
fermentation activity has stopped that it also needs to be given
time to clear as well before bottling. Yeast is a silty substance that

can take up to 2-4 additional weeks to clear up once the ferment-

ation has stopped.


- Related Articles:
"Top Ten Reasons For Fermentation Failure"

 

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