HOW TO STOP A FERMENTATION

Quite often we'll have someone ask us how to stop a fermentation
before it is ready to stop on its own. Usually the reason for
asking is because they have tasted their wine and they like the
amount of sweetness it currently has--sounds reasonable.

Stopping the wine from fermenting any further would preserve the
current level of sweetness. And likewise, allowing the wine to
continue fermenting further would only make the wine less sweet
with each passing day.

Eventually the wine would become completely dry at which time the
fermentation would stop on its own. This is because during the
fermentation process yeast turns the sugar into alcohol.

Wanting to stop a fermentation is all good in of itself. But
unfortunately, there is really no practical way to successfully
stop a fermentation dead in its tracks.


- Using Sodium Bisulfite or Campden Tablets

Many winemakers will turn to sulfites such as that found in
Sodium Bisulfite or Campden Tablets for the answer. But, these
two items are not capable of reliably killing enough of the yeast
to guarantee a complete stop of the activity--at least not at
normal doses that leave the wine still drinkable.

Once the bulk of the sulfites from either of these ingredients
dissipate from the wine into the air--as sulfites do--there is a
very strong chance that the remaining few live yeast cells will
start multiplying and fermenting again if given enough time. And,
I might add that this usually happens at a most inconvenient
time, like after the wine has been bottled and stowed away.


- Using Potassium Sorbate

Potassium Sorbate is another ingredient that many winemakers
consider when trying to stop a wine from fermenting any further.
There is a lot of misunderstanding surrounding this product.

It is typically called for by home wine making books when
sweetening a wine. This is a situation where the fermentation has
already completed and is ready for bottling. You simply add the
Potassium Sorbate along with the sugar that is added for
sweetening.

The Potassium Sorbate stops the yeast from fermenting the newly
added sugar. So, many winemakers assume Potassium Sorbate can
stop an active fermentation as well. But, nothing could be further
from the truth.

Potassium Sorbate does not kill the yeast at all, but rather it
makes the yeast sterile. In other words, it impairs the yeast's
ability to reproduce itself. But, it does not hinder the yeast's
ability to ferment sugar into alcohol.

Potassium Sorbate puts a coating on the cell wall of each
individual yeast in such a way that budding or multiplying is
next to impossible.

The idea here is that if you happen to have few cells of live
yeast remaining in your finished wine, they will be rendered
harmless if they are unable to regenerate themselves to great
enough numbers to invigorate a fermentation of any kind. This is
true even if more sugar is added to the finished wine.


- So, What Do You Do?

Well, remember the original goal here is to have a wine that is
sweeter than what a natural fermentation will normally provide.
And what the above tells us is that stopping a wine's ferment-
ation in mid-stream when it is at the sweetness you like is not
the answer for the average home wine maker.

The most successful way for a home wine maker to have a sweet
wine is to let it finish fermenting completely to where it is
dry. Then let the yeast settle out to the bottom on its own over
a 2 to 3 week period. The settling process can be sped up with
the use of a clarifier such as Speedy Bentonite.

Once this happens you can then siphon the wine off of the yeast
settlings and add Potassium Sorbate and Sodium Bisulfite as
directed on their packages. Once you have done this you can then
simply sweeten your wine to taste with a sugar mixture of your
choice.

It is important that the wine's fermentation process be complete
before adding more sugar along with Potassium Sorbate and Sodium
Bisulfite to a wine. One way to make absolutely sure is to check
the wine with a hydrometer. The wine should have a reading of
1.000 or less on the hydrometer's Specific Gravity scale.

You might want to take a look at another article on our web site
titled, "Making Sweet Wines." It covers in detail the process for

making a sweet wine.