Basic Barrel Care Techniques
Dermott Dowling
Here we share some tips and tricks learned along the way on how to take care of your beloved barrels for brewing and distilling.
Buying a Barrel:
When you first buy a barrel, new or used, thoroughly inspect the interior
and exterior of the barrel for any potential problems. Visually inspect the
interior by inserting a small light source through the bung hole. Look for
any obvious wood defects, wide joint gaps, or excessively charred wood
resulting from over-toasting. Barrels are toasted in an open fire during
manufacturing. Toasted wood should have a smooth finish with a uniform
brownish color. Charred wood will look damaged and can be easily
detected because it has a very dark brown, almost black, color.
On the exterior, ensure that stave and head joints are narrow and tight,
hoops are properly fastened, and the bung hole is tapered and not
damaged — a source of spoilage problems. Old barrels may have a crack
emanating from the bung hole, which may cause excessive oxidation
New Barrel Maintenance
To minimize maintenance, wait to buy new barrels until you are ready to use them. Otherwise, store empty barrels in a cool and humid area, 55° F
(13° C) and 65–75 percent humidity, respectively, and away from
dampness, to minimize shrinkage. If the wood shrinks, stave and head
joint gaps will widen and barrels will require more preparation when ready
to transfer your wine.
Protect empty barrels from spoilage organisms by burning sulfur inside the
barrels to replace the air with sulfur dioxide (SO ) gas. Barrels can be
stored empty for an indefinite amount of time when properly preserved
with sulfur. Once a month, gently sniff the inside of each barrel to
determine if any SO gas is still present. If detected, simply replace the
bung; otherwise, burn more sulfur. Be sure to work in a well-ventilated
area and avoid inhaling SO gas.
INSPECTING AND TESTING NEW BARRELS:
On their arrival at the brewery, distillery or winery, new barrels should be assessed carefully for:
- biosecurity incursions, including borers or other insects
- physical structural integrity, to ensure they have not been damaged during transport
- absence of microbial contamination or mould growth
- taint aromas potentially imparted during transport, including halophenol/plastic taints, TCA and/or mouldy aromas.
Before first use, new barrels of size around 300 L should be filled with 20 L hot water (60-80°C), rotated side to side to wet the entire inside of the barrel, then stored vertically for 2-4 hours, then inverted to the other head for 2-4 hours and then drained. Alternatively, barrels can be filled with 20 L cold water and stored for 12 hours on each head. Barrels should be checked for leaks after this process. Water used should be chlorine-free, which can be achieved using in-line carbon filtration of mains water or by using heated water. If barrels are stored dry for more than one month, then the barrel should be completely filled with cold water and left for 48 hours, checked for leaks, emptied, rinsed, drained and allowed to dry completely (1 hour) before first-time use. If new barrels are still leaking after 48 hours, it is recommended to contact the supplier. Barrels should not be left filled with water for more than 48 hours, to prevent water-borne microbiological growth and taints. Barrels should be drained and refilled with fresh water if required.
A new barrel must be swelled with clean water before transferring wine
into it; otherwise, it will leak. If wine leaks through stave or head joints, or
the croze, there may be considerable wine loss. There may also be
premature oxidation of the wine as air enters the barrel. Eventually, if
untreated, mold will form on the exterior surface and will penetrate through
the joints to contaminate the wine. By swelling barrels, all joints will tighten to eliminate any possibility of wine seepage and prevent spoilage problems.
You can swell a new barrel using a hot-water treatment or using an
overnight water-soaking treatment. First, let all the SO gas out and
thoroughly rinse the inside of the barrel with lukewarm water.
The hot-water treatment method is very effective and requires little water.
Pour approximately a 20 percent volume of very hot, steamy, clean tap
water into the barrel. For example, use three gallons (11 L) of hot water for
a 15-gallon (57 L) barrel. Bung the barrel and slosh it around to soak the
entire interior surface. The vapor pressure and hot water significantly
accelerate barrel swelling and “plug” any seepage through joints. Continue
sloshing the barrel until there is no more leakage. Then place it upright
and let the head area soak until there is no more leakage, and repeat with
the other head area. When done, let the water drain completely and let the
barrel dry and cool down before transferring wine into it. If the barrel does
not stop leaking within one hour of pouring the hot water, proceed with an
overnight treatment.
The overnight treatment will always fix any leakage (unless the barrel is
defective) although it will leach out some of the oak flavor owing to the
longer soak period. This is fine for new barrels because you may want to
reduce the amount of oak that will be imparted to that first batch of beer or wine or spirit. The overnight treatment is also the best method for swelling a barrel that has been in dry storage for a long time.
Fill the barrel to the top with cool water and let it soak overnight. Initially,
the barrel may leak but it should stop after a few hours or a day, or up to
several days for very dry barrels. The soak period should never exceed
24–36 hours with the same water to avoid mold developing and
penetrating the barrel. If there is still leakage, empty the barrel and fill it
again with clean cool water, and repeat again until leakage stops. If
leakage does not stop after four to five days, the barrel is defective and
should be returned to your supplier. When leakage has stopped, drain the
water out of the barrel by placing it in the bung-down position. Let the
barrel stand for an hour or two and then fill it immediately with your beer, wine or spirit.
The barrel’s exterior surface requires no special preparation, although you
should inspect it regularly for any mold.
Used Barrel Storage, Maintenance and Preparation
CLEANING USED BARRELS
Once emptied of wine, barrels should be inverted to near the 6 o’clock position, drained and then rinsed with high pressure (100-3,000 psi) cold water for three minutes using a barrel washer with a rotating spray head. Rinsing helps to loosen and remove the gross sediment, which generally consists of yeast lees, pigments, proteins, polysaccharides and tartrates. Hot water rinsing at 60-82°C for three to five minutes may then be required to remove persistent colour or tartrate coatings on the internal barrel surface, with tartrate much more soluble in hot water than cold. Visual inspection of the cleaning efforts can be made via the bunghole with aid of a light. Harder persistent tartrate deposits may require higher temperatures, steaming or alternative treatments.
A barrel washer generally contains a rotating spray head attached to stainless steel pipe and framework that can be inserted into the barrel through the bung hole. Pressures used can vary from 100 – 3,000 psi(689 – 20,684 kPa) (Yap et al. 2007). There are a variety of barrel washing apparatus options available, some of which are semi-automated. Barrel washers generally require a portable steam generator that connects to the barrel washing device. Steam generators can reduce both water and energy use, and can be used for general cleaning as well as barrel cleaning. The units use dry saturated steam, where 98% of water has been converted into a gas, rather than wet steam or boiling water.
Chemical treatments are preferably avoided. Citric acid (5 g/L) can help dissolve tartrate deposits but may react with cellulose of the wood and possibly compromise staves over time. Sodium carbonate, potassium carbonate or sodium peroxycarbonate (2 g/L) can leach out oak flavour. Chlorine solutions should be avoided due to the risk of forming chlorophenol and chloroanisole taints. Chitosan has been adopted by some winemakers to reduce Brettanomyces cell numbers in affected wines but no information is available on its ability to treat affected barrels.
Used (sound) barrels must also be properly stored and maintained;
however, since these previously contained wine, a different maintenance
program is recommended. If used barrels are to be stored empty, rinse them several times with clean water, drain and then burn sulfur inside. Check for the presence of SO gas once a month, and replenish as required. The disadvantage of this method is that the barrel wood will dry and shrink over time, and will
therefore require to be swelled again when transferring wine into it.
An effective alternative is to fill and store barrels with a sulfur-citric holding
solution. This holding solution will promote sterility, keep the barrels
swelled and smelling sweet. It is not recommended for new barrels or
barrels less than one year old as precious oak extract would be stripped.
The holding solution is prepared using 1 tsp of citric acid and 1.5 tsp of
potassium metabisulfite for each gallon (4 L) of barrel volume. For
example, for a 15-gallon (57 L) barrel, use 15 tsp of citric acid and 23 tsp
of potassium metabisulfite. (Note: 3 tsp = 1 tbsp) Dissolve these in one
gallon of hot water. Fill the barrel two-thirds with water, add the holding
solution, top up the barrel with cool water, and bung the barrel. Top up the
barrel with a holding solution once a month to replace solution lost by
evaporation and absorption into the wood. The barrel can be stored
indefinitely without the risk of spoilage. During storage, rotate the barrel
45° in either direction every time you top up to keep the bung area
soaked. This will prevent the bung area from drying out and protect it from
spoilage organism growth. Caution: The sulfur-citric holding solution will
etch a concrete floor. Rinse the floor with water to prevent this.
Used barrels require no special preparation beyond a simple water rinse, if
desired, when transferring wine out and in immediately. If the barrel has
been stored with a holding solution, drain the barrel and rinse it thoroughly
with clean water before transferring wine into it.
Sanitizing A Barrel That Has Already Been Used
Use this procedure to sanitize your barrel before filling it with beer or wine.
1. Fill barrel halfway with cold water.
2. Add 2.5 grams of Potassium Metabisulphite for every litre of the barrel’s total volume.
3. Add 1.25 grams of citric acid for every litre of the barrel’s total volume.
4. Bung the barrel. Roll it to mix in the Potassium Metabisulphite and citric acid.
5. Remove bung and finish filling barrel with cold water. Replace bung and let full barrel stand 48 hours.
6. Drain barrel. Rinse several times with cold water.
Types of Barrel Spoilage Problems
Oak barrels will not cause any problems when properly maintained. In
improperly maintained barrels, however, spoilage problems can occur because wood is a good breeding medium for bacteria and other spoilage organisms, especially in the presence of water or wine.
Penicillium mold — a blue-green fungus causing foul-smelling odors when
it interacts with wine — is the most common spoilage problem and can be
very difficult to eradicate if widespread. Typically, it will grow through stave
or head joints, or the croze, and around the bung hole in barrels that have
not been properly swelled prior to transferring wine.
Another common source of spoilage is Acetobacter (acetic acid bacteria),
which cause alcohol to be converted to acetic acid when wine or beer oxidizes in barrels having a headspace. Acetic acid will cause volatile acidity (VA)
and can be detected as the familiar vinegar smell.
The spoilage problem can also occur in empty barrels that have not been
properly rinsed or sulfured during barrel storage, and where some wine residues were left behind. As this problem grows, the acetic acid combines with alcohol residues to form ethyl acetate, which smells distinctly like nail-polish remover and is very difficult to eradicate.
Brettanomyces yeasts resident in barrels are another source of problems.
These spoilage yeasts can metabolize extremely low levels of sugar in wines, even wood cellulose sugars in new barrels. They result from insufficient sulfiting of wines or insufficient sulfuring of empty barrels during storage. Advanced yeast spoilage will cause a wine or barrel to take on a “medicine cabinet” smell.
Lactobacillis and Pediococcus (types of lactic acid bacteria) resident in barrels can also cause spoilage in wines with a very high pH (above 3.7) and a very low level of sulfite. They can also cause spoilage in wines with residual sugar. These bacteria thrive in such an environment and can impart a sour-milk taste to wine. They are best inhibited by maintaining at least 70 mg/L of free SO in wines and by periodically racking the wine from its lees.
Dealing with Spoilage Problems
To treat any of the above spoilage problems, first fill the barrel two-thirds with cool water. Prepare an alkaline solution by dissolving either sodium carbonate or sodium percarbonate in water at a rate of 1 tsp per gallon (or use 1 g/L) for mild spoilage problems or up to a maximum of 3 tsp for more serious problems. Add the solution to the barrel and then top up with water.
Let the barrel soak overnight, empty it and neutralize any remaining
alkaline residues using a citric acid solution. Trace residues of sodium
carbonate or sodium percarbonate are not harmful but they will affect the
taste of wine if allowed to come into contact with it. Prepare the citric acid
solution by dissolving citric acid powder in one gallon of water. Use 1 tsp.
of powder for each gallon of barrel volume. For example, dissolve 15 tsp
for a 15-gallon (57 L) barrel.
Fill the barrel two-thirds with cool water, pour in the citric acid solution, top
up with cool water, and let the barrel soak overnight. Then, empty the
barrel and rinse it thoroughly. Drain the water completely and let the barrel
dry. Smell the barrel for any off odors to ensure the treatment worked. If
the barrel does not smell completely clean, repeat the treatment as
required. Discard the barrel if the problem cannot be eliminated. Don’t risk
spoiling a perfect batch of wine.
SANITISING BARRELS
Microorganisms typically grow in the wine liquid in the barrel, often at the wine/air interface, with increased risk in ullaged barrels or barrels that have not been regularly adjusted to maintain adequate sulfur dioxide levels. Microorganisms can also migrate up to 8 mm into the barrel wood as wine soaks into the wood. This makes it more difficult to completely sanitise a barrel than an inert vessel such as a stainless steel tank. For this reason, barrels must be rigorously cleaned prior to sanitation, to remove any gross solids and colour or tartrate coatings on the surface of the barrel that may impede any sanitation treatments reaching into the barrel wood.
SANITATION USING STEAM
In recent research on barrel sanitation (Barata et al. 2013), steam was successful in removing yeast from the cleaned internal surface of the barrel and up to 2 mm into staves, However, none of the treatments tested, including high pressure hot water, steam, ozone, SO2 dissolved in water or SO2 gas were successful in guaranteeing yeast deactivation in grooves or up to 8 mm depth in the staves. More recently, Solis (2018) found steaming was required for at least 10 minutes to achieve temperatures >57.5ºC at a depth of 8 mm within a barrel, which was the temperature required to kill Brettanomyces in this study.
SANITATION USING HOT WATER
Treating barrel wood with hot water (at least 85°C) for 20 minutes has been shown to be successful in eliminating viable acetic acid bacteria, with the water found to be at about 60°C at the end of the 20 minutes (Wilker and Dharmadhikari 1997). Coulter et al (2003) extrapolated this finding to suggest that filling barrels with hot water at 85°C and holding for 15 minutes was required to eliminate Brettanomyces -infected barrels. A recent study confirmed hot water treatment as an effective option, finding that holding water at 70°C for 30 minutes or 80°C for 20 minutes was able to eliminate Brettanomyces yeast from barrel wood at wood depths of up to 5-9 mm (Edwards and Cartwright 2018).
These temperatures can be achieved by filling barrels with 70°C hot water, the typical temperature achieved from a hot water system, and increasing the temperature by inserting the nozzle from a hot water pressure cleaner. Minimal drop in water temperature occurs over an hour, such that the water can be re-used three or four times before re-heating. Transfer of hot water between barrels could compromise pump impeller integrity, with syphoning an alternative, using a large diameter hose with a metal swan-neck fitting in the top barrel in order to prevent the hose from flattening due to the heat.
Barrels can be tested after sanitation steps by adding 4 L of sterile water or preservative-free filtered wine to a sanitised barrel, rolling the barrel from side to side, then leaving it for 24 hours. The liquid can then be sampled and tested for viable microorganisms.
HOW SHOULD BARRELS BE STORED?
New barrels can be left in plastic film and stored in a clean area with 65-75% humidity. If used or emptied barrels are not to be immediately refilled with wine, then they can be stored dry or wet.
Dry storage involves burning elemental sulfur producing gaseous SO2 within the barrel or directly filling the barrel with SO2 gas. Sulfur rates are around 10 g ring/barrel, or 1/3 sulfur stick/barrel, or alternatively use 1.7-3.4 g/barrel using a flameproof holder inserted into the barrel. Then tightly insert a silicon bung. Barrels should be assessed every 4-6 weeks to ensure sufficient gas is still present, or the process should be repeated. After more than one month’s continual dry storage, barrels should be rinsed and then filled with cold water and left for 48 hours to reswell/hydrate, checked for leaks, then drained.
Wet storage involves filling barrels to a 10% volume using an acidified SO2 water solution. Note that some of this volume will evaporate with time and some will soak into the wood of the barrel, so lower volumes are not recommended. Use chlorine-free water and add citric or tartaric acid to ensure pH<3.0, generally 5 g/L, and an SO2 addition of 500 mg/L potassium metabisulfite. This solution should be topped up every 4-6 weeks.
Rinsing the barrels after wet or dry storage is very important as any residual elemental sulfur or SO2 can lead to greater levels of bound SO2 in must or wine added to the barrel and could inhibit yeast or malolactic acid fermentations and/or increase risks of sulfide formation. Residual acid in barrels following wet storage can also have a negative impact on wine if it not rinsed away.
Red wine stains, vinegar flies or mould or microbiological growth on the outside of barrels (particularly around the bung hole and often caused by spills or insufficient cleaning after topping or sampling) can be removed with a scrubbing brush and using a crude solution of 1:1 solution of SO2 and citric acid, followed by rinsing the area with water. Again, use of chlorine should be avoided on wine barrels. Larger occurrences of mould can indicate that the cellar humidity is too high (>75%).