This article is from the WineMaking FAQ, by malak@CAM.ORG (Don Buchan) with numerous contributions by others.
Red wine fermentation: the trick with red wine grapes is to hit a peak
temperature near 32C (90F) for at least a short time to optimize colour
Pros naturally achieve temperature -- the large fermentors they use
don't allow the heat of fermentation to escape easily. Some must even
prevent overheating! With our small tubs, we amateurs must use
trickery. The best heating system is a "brewbelt" which should be
available from a local brewing supply store. A simple trick is to wrap
an electric blanket around the fermentor. A submersible thermometer
will tell you when you've got the right thermostat setting. Other heat
sources are aquarium heaters, space heaters, and waterbed heaters.
A good fermentation regimen is to hold the must at 4C (40F) for 5 days,
innoculate and warm to 32C (90F) for a day, then drop the temperature
down into the 15C to 26C (60F to 80F) range for a long fermentation,
pressing a couple days after cap fall.
Cold fermentation: Some white wines benefit from a cooler fermentation,
producing a clean, fruity wine.
Again, cooler fermentations can be difficult. An old fridge run warm
(about 10C (50F)) is perfect for a carboy at a time. Icebags suspended
in must or placed in a tub in which a fermentation vessel sits can be
effective. You can place carboys in tubs of water on the basement floor
if it's cool. The water draws heat from the carboy to the floor. A good
target temperature for white wines is 10C to 13C (50F to 55F).
Barrel fermentation: It's not hard once you get past the expense of the
barrel. Press the grapes in the usual fashion, settle the juice
overnight. Rack the juice into the barrel (previously swelled to
prevent leaks) to about 80% full. Inoculate with yeast, put an airlock
in the bunghole and wait. After about 2 to 3 weeks, when vigorous
action has slowed, top the barrel off and keep it topped. Leave it in
the barrel for anywhere from 3 weeks to a year, depending on many
factors (age of oak, desired amount of oak flavour, etc.)
Malolactic fermentation: MLF, as it is abbreviated, is a bacterial
fermentation where sharp malic acid in wine is converted by bacteria to
mellower lactic acid. MLF is usually good, especially for high acid
Chardonnays. Pinot Noir, which has a high natural malic acid content,
almost always undergoes MLF and benefits from it. The MLF bacteria
sometimes can be present on either the grapeskins or your facility and
equipment and is available for purchase at most wine supply shops.
If you want MLF to happen, keep sulphite down. MLF is sensitive to
sulphite, low pH's (especially below 3.0), and cool temperatures (below
15C (60F)). If your pH is very low, the wine can be partly neutralized
to raise the pH. Be careful at this point as adding too much chalk can
add a chalky taste to the wine. See section G21. ACID BALANCE. So,
inoculate early -- many do it soon after yeast fermentation has started
(the must is warm and has little sulphite). Doing it early also avoids
the culture being killed off by high alcohol levels during
innoculation. Don't fine the wine until after the MLF is finished as ML
bacteria like the solids, and add a nutrient good for MLF. MLF survives
very well in barrels, so if you are putting your Pinot in a barrel that
has held a wine that has undergone MLF, it will take off on its own.
This has historically been a common occurence in the spring following
The lees in the barrel or carboy harbour the bacteria, so leaving wine
on the lees until late spring can encourage MLF. Some wines, like
Riesling, don't like MLF. A moderate sulphite dose almost always
provides adequate protection against it and other bacterial
You can tell that MLF is happening in 3 ways. One is to use
chromatography to measure relative malic and lactic acid levels.
Another is to notice the onset of renewed CO2 action (bubbles) well
after the yeast fermentation is done. Another is to taste the change in
the wine from sharp to more mellow and buttery.
When this is done this in a winery, it's usually in conjunction with
barrel fermentation. Hence, the primary lees are the ones that are
stirred. Having said this, it should be pointed out that the juice has
been racked once before inoculation so the solids are in the lees than
2% range in the juice at inoculation.
Stirring frequency is up to the winemaker but even no stirring will
result in what is described as a greater mouthfeel. This can lead to a
sense of richness, softness and definitely better integration of oak,
malolactic character and fruit. Many wineries start off stirring weekly
(originally the stirring was done to encourage malolactic fermentation)
and then gradually tapering to once every two weeks to once a month
with usually the end being at 6-9 months depending on taste. And that's
the most important indicator. Sometimes, there can be a sulphide
problem, so you have to taste the wine throughout the process. If you
push the wine through MLF you shouldn't have a bacterial problem. Also,
once MLF is complete you should add some sulphite to avoid bacterial