How to Maintain Oak Barrels

This information is based on my experience with wine rather than beer, but principles still apply. Traditional beer barrels are thicker, as they have to withstand pressure and fairly rough treatment to and from pubs. ‘Roll out the barrel’ gives you some idea of the punishment they take! Counteract that by learning how to maintain oak barrels.

Cider also benefits from cask maturing, as do spirits. Grape spirit cannot be classed as brandy until it has spent a year in cask. In the UK, the distillation of alcoholic beverages, even just for personal consumption, is a civil offense, subject to a minimum fine of $361.

Brandy is made from the distillation of wine made from grapes which do not make good wine. I once considered making brandy from a considerable crop of apples, since I was unimpressed with both the cider and the wine they produced. It would require about 130 pounds of apples to make to make enough cider to produce 1.3 gallons of raw spirit, plus the cost of the still and the cask…

The word ‘barrel’ is actually a specific capacity of 36 imperial gallons (of beer), whereas ‘cask’ is a generic term. Keg is also a generic term, but usually refers to metal containers and gas pressure. The word gallon derives from a cask of that capacity, a ‘pin’ holds 4.5 gallons, a ‘six’ is 6 gallons and a ’firkin’ is 9 gallons and so on. US gallons are smaller than imperial ones. Crude oil is still measured in terms of barrels. A gun barrel is so called due to its cylindrical shape but ‘barrel-chested’ has rather more to do with bulge! The bulge or bilge in the typical shape serves 2 functions, it makes it easy to roll in any direction and also concentrates sediment at its lowest point. However, shapes vary. The oval cask, for instance, was designed to save space. I will use the word cask and mostly refer to the pin size.

For years I toyed with the idea of growing my own grapes and maturing wine in oak casks. I now have a small (100 vine) vineyard and 8 casks of various sizes filled with wine. I was of course initially put off by high initial costs and long timescales plus maintenance and storage issues. Even after 4 years of having all these facilities, output is still quite low, quality is variable and the cost per bottle is about $14, considering the investment costs.

coverI bought my first cask second hand at a boot fair for $11.50. It was oval, rather than round, held about 10 gallons but had no bung, stand, tap hole or tap, had a missing hoop and leaked, but water came out without any taint or stain. I bought a cork bung, wooden/plastic tap, made a new hoop from a strip of mild steel, fixed with a rivet, cut a hole and fitted the tap, made a stand and fixed the leaks with silicone sealant. I followed complicated and long-winded instructions for internal preparation and filled it with white wine made from my neighbor's huge vine, stored it for 6 months, bottled it, labelled it and found the wine somewhat mediocre. Much to be learned! The cask itself was not to blame, although old casks become exhausted. They cease to confer quality to their contents and get consigned to water butts and garden planters. However they can get a new lease of brewing life. There was a case of a whiskey distiller who bought old sherry barrels to save money. He was impressed with the flavor they conferred on his brews. He eventually sold them back, or exchanged them, with the sherry producer, who was equally impressed with the whiskey flavor!

The real problem was that the grapes had been harvested too early and 6 months in an old cask did little to improve the resulting wine. Garbage in, garbage out. I refilled the cask with better quality pinot noir from my vineyard but again the results, though better, were unimpressive. After all, I had no idea what it had been used for or even the wood it was made from. Flavour can be restored by suspending a length of new oak inside the cask. Otherwise a new cask is required.

The most commonly available used casks are old whiskey barrels, of 36 gallon capacity, and so too big for the typical home winemaker. I did buy a convincing-looking 5 liter cask at a boot fair which turned out to be a plastic imitation with a glass liner of 3 liter capacity!

New casks are expensive, mostly on account of the skilled labor required to make them. A 5 liter one cost me $72 and a 50 liter one cost $130! I have seen 20 liter complete sets for $216! For a typical home brewer, the best sizes are 5 and 20 liters, the latter being the better value for the money and probably the absolute minimum for maturing white wine. The oak should be French or American. Chestnut casks are a bit cheaper, although I have not tried one. Polish and Italian made ones are cheaper but shipping costs wipe out the price advantage.

Most in this size range are supplied with a wooden tap, which always seep and usually drip. Worse still, they attract fruit flies as a result and encourage infections. Some even come with a nicely turned oak drip bowl!

fillinThey are not intended as a permanent fixture for those reasons, although the vendors don’t point this out. They should never be fitted during transportation. The tap hole should be plugged with a cork bung (not usually supplied) which is driven into the cask by the tap with the aid of a mallet when the wine is ready for racking or bottling. I had to make my own by paring down a synthetic wine cork. The bung is recovered from the cask through the top bung hole and is used to replace the tap on refilling. The tap hole can also be used for racking the wine as there is little or no disturbance of the sediment.

A stainless steel tap is best as it can be regarded as a permanent fixture and is unaffected by acid, unlike copper. The 10 and 20 liter barrels came with wooden tapered taps with a mere 3 mm outlet diameter and therefore are very slow. I replaced them with stainless taps with a straight ½ inch thread which cuts into the wood around the existing hole and has a thick silicon seal which is tightened with a nut. The outlet is 10 mm and fills a bottle in a few seconds. I bought these on eBay, post free from China, for $7.

The 5 litre one came with an even smaller tap and the hole had to be enlarged to fit the replacement. This proved difficult as the drill bit had nothing to grip to keep it centred.  A cork bung will not last as long as a solid wood one (but these can be tricky to remove). It also had a bung hole which was too narrow to take a sediment trap on the siphon tube, and had to be enlarged, with the same problem.

It is common practise to turn the cask 60 degrees so that the bung is kept wet, reducing evaporation. I have found that only a wooden bung is suitable because a cork one would have to be hammered in so tight, removal without damage is very difficult, while a rubber one would taint the wine. Removing a tight wooden bung requires tapping around it with a mallet. Some wooden bungs are shaped with a knob so they can be gripped and pulled. A cork bung will not damage the bung hole and a rubber one does not need to be kept wet.




Another thing to be aware of is coatings. Some come with a coat of varnish and even an internal coating, defeating the whole benefit of the wood breathing! However, to compensate for the high rate of evaporation and consequently fast oxidation with small sizes, a coat of varnish on the stave ends of the cask can be an advantage, particularly with white wine, because evaporation is greater there.

Capacity sizes are nominal. I have a 5 liter which holds 5.5 liters, 20 liter ones which holds only 18.5 liters, a 7 liter which holds 9, and a 50 liter which holds 60.20 liters. Casks are in fact the traditional ‘pin’ of 4.5 gallon (18.5 liters) capacity. As is the tendency with metrication, sizes are inaccurately rounded, as with VAT, which was supposed to replace purchase tax, but was simply added on top, effectively doubling the tax. Give them an inch and they will take a mile.

A typical ‘30’ bottle kit starts off at about 23 liters of ‘must’ and ends up with around 21 liters of wine. So after filling the cask there will be about 2.5 liters spare, which will come in use later. Being porous, a wooden cask loses moisture over time, leaving a growing airspace. This contains oxygen which interacts with the wine and improves the flavour. However, too much oxygen, especially with white wine (but not sherry) will spoil it. A pin size cask loses at least 100 ml (more if a wooden tap is fitted) of liquid per month and should be topped up at these intervals. Most of this is purely water. It can be replaced with just water, which will maintain the balance of the wine, or slightly enriched by topping up with the spare wine, which can also be used to monitor the amount of sediment forming. Because alcohol does not evaporate as readily as water from the cask, the abv will slowly increase as the volume decreases. This could be considered an advantage by some and, in the case of certain wine kits, actually is! The rate of evaporation depends on air temperature and humidity. 12 c  and 75% humidity is an ideal combination to minimise it.

The sediment plays an important part in the development of aroma. The yeast content interacts with the wine (autolysis). Too much yeast sediment, however, will confer an unpleasant taste. Usually, excess sediment is removed after primary fermentation and the rest is removed by fining. However this fining is omitted if the wine is destined for a cask. Fining removes some tannin and makes the wine smoother if consumed young. By omitting fining, this tannin retains preservative qualities and not only helps the wine to clear naturally but gradually gets transformed into a less astringent form, which is why an old claret tastes much better than a young one and of course, costs more as a result! Traditionally the wine in the cask is racked off the sediment every 4 months until it is considered ready for bottling.

This raises the crucial question of time. I have found that most red wine in this size cask is usually ready for bottling after just 4 months and whites just 2 months. The reason for the difference is that anthocyanin, which gives the red color, is an anti-oxidant and the extra tannin, extracted from grape skins and pips, helps preserve the wine better. The smaller the cask, the faster the rate of maturation, but the slower the maturation, the better the wine.

Most casks are stored horizontally when full. If stored vertically, the rate of evaporation is greatly increased. Sizes under 50 liters are usually supplied with a stand to keep the belly clear of contact with the surface on which they are placed. Larger sizes will barrequire a stand or other suitable means of support to be made or supplied before filling. New casks should be completely filled with water and will leak until the wood has expanded, so the water level needs to be maintained until watertight. If leaks persist after 48 hours soaking, contact the supplier.

Although soaking with water expands the cask, the capacity of small casks does not significantly increase as it is restricted by the mild steel hoops, which do not stretch as much as the wood would like. However, the last 2 casks I bought have stainless steel hoops which seem to stretch more. Hence a 7 liter one expanded to 9 liters and the 50 liter one to 60 liters. The larger the size, the greater the expansion, but the longer it takes. In the process of filling the large one with wine, I was constantly having to top it up at an alarming rate, suspecting a leak. An extra 10 liters of wine is not easy to source in the short term! Eventually it peaked at its maximum.

A new cask needs to be conditioned after initial soaking, otherwise it will confer too strong of a flavor which will certainly spoil a delicate white wine and even make a robust porter taste somewhat strange. I neglected to do this with an elderflower wine in a new 9 liter cask. The delicate flavor was completely overwhelmed by the oak. This is where the spare wine from a 30 bottle kit can be put to good use or any wine which may be considered worth sacrificing for the greater good. Pour a bottle of it into the cask and thoroughly swirl it around for about 10 minutes, contacting all internal surfaces. If it comes out tasting bad, then it has done its job. I recommend initially filling the cask with an inexpensive red wine kit, which will actually be much improved by the new oak effect. Ideally the wine is fermented down to SG 1.010 in a bin and then racked into the cask. The bung must be bored out to accept a fermentation trap, which in turn can be replaced with a suitable plug, such as a pencil stub. The wine is left to complete this secondary fermentation and natural clearing. There is no point in using a cask if you want quick results, but a white wine should be left for only a month in a small (20 liter) cask before final racking and, if required, fining before bottling. Cask fermentation is a good way to condition the wood, and need only be done once for this purpose. Each subsequent brew gains something from the previous and adds to the next. You can swap from red to white, but expect a pink tinge to the latter!

Sherry is a special case. A permanent air space is caskrequired for a good supply of clean oxygen over a long period to attain the special flavor. It is also suitable for dispensing by glass from the tap, but dry sherry should be chilled. Since sherry is not something I consume in bulk, a 5 liter batch was all I might require. Sherry is matured on the solera system, requiring 3 casks. A third of of the oldest is bottled and a third of the second oldest is added to replace it. A third of the newest is added to the second newest and replaced with a third of the oldest. My simple shortcut was to buy a bottle of fino and add it to my young brew in the cask! In the unlikely event of me doing another brew, I would simply reserve a bottle and add that. This is a case where the 7 liter cask has come into its own. I bought this at a boot fair for $57, brand new, handmade, and complete with stand, metal tap and wooden bung. In my ignorance at the time, I failed to condition it other than soaking with water. I put my basic fino sherry in, topped it up, plugged it with cotton wool and left it for many weeks, hoping for the elusive flor yeast to develop. This did not happen and the only reason it tastes like fino is because I added it! There is also a slight new oak taste and color which is a bit detrimental, but to be fair this robust extra dry brew of 16% abv has stoutly countered the new oak with dignity. Unfortunately half of it had evaporated, including the alcohol, leaving just 3 bottles, so I must conclude that this size cask is unsuitable for long term maturation. I have now filled it with red wine in its final stage of fermentation, as I should have done in the first place.

A porter is another brew worthy of cask conditioning. Usually consumed in small quantities, it’s another strong candidate for the 5 liter cask, but expect high loss through evaporation.

The golden rule with casks is not to let them dry out, which would cause shrinkage and subsequent leaks. Ideally, once empty, they should be immediately completely refilled with the next brew, after rinsing out. This is not always possible, in which case sulphited water will do, but only about 10% of its capacity is needed to maintain moisture until the next brew, provided the delay is short.

When the wine is ready to bottle, the cask must be emptied completely, requiring lots of bottles. What I tend to do is siphon the whole lot into a polypin and dispense the wine from that. Either way, the wine gets disturbed and needs time to recover for up to a month before drinking.

If a permanent tap is fitted, the wine can be easily sampled for clarity and flavor, but bear in mind that red wine should be left to reach room temperature before tasting. If no tap is fitted, a syringe or turkey baster can be used to extract a sample from the top. This runs the risk of infection and can be misleading, as wine at the top may be clear, but not further down.



While it is possible to dispense wine from the tap on a per glass basis without removing the top bung, this creates a vacuum which will slowly draw in air through the wood’s pores with no risk of bacterial infection, the worst offender being acetobacter, which turns alcohol into acetic acid – vinegar. However wine further improves in an airtight container, such as a bottle or polypin. The process is called esterification.

Location is important. Wine (except Madeira) is best stored at a stable cool temperature, a cellar being the obvious ideal location. For cleaning, a water supply and drainage cellaris very helpful. I keep some in the north facing unheated spare room and others in the north facing back yard, which receives no direct sun, but is subject to frost. Height is also important. You don’t want to be bending or stretching too much (especially at my age!) and waist height is a good compromise. The tap should overhang for ease of emptying. Lifting a full pin is best avoided to avoid back strain. Filling is best done one gallon at a time via a funnel. Without a tap, bulk emptying of wine is best done with a 10 mm self-priming syphon fitted with a sediment trap into a 5 gallon fermenting bin or polypin. The latter is the best option for subsequent dispensing and bottling. I recently filled 56 bottles directly from the 10 gallon cask via the tap in a single session. It was a tedious business.

In-cask fermentation may occur if the wine has not been stabilised. Most of my wine is dry, so there is no risk of a yeast re-fermentation. However, as I do not use sulphite and often use fresh ingredients which contain malic acid, (e.g. grapes, apples, peaches) there is a good chance that a malolactic fermentation may take place even at temperatures as low as 50F. This will create pressure inside the cask and may pop the bung, exposing the wine to unlimited bacteria and excessive oxygen. This has occurred more than once, so I now fit an airlock to the bung, allowing excess co2 out. I am generally in favor of malolactic fermentation but it can be suppressed with sulphite.

Sweet wine is best established with sorbate unless it is of high (15% +) alcoholic strength, to prevent re-fermentation. However, I had a white wine which had ceased fermenting at SG 1.005. As I had intended to make this into a bottle-fermented sparkling wine, this seemed neither safe nor possible, but after a month in the cask it started to ferment and went down to SG 1.095, thus making the sparkling wine project possible.

Wine made from fresh grapes and ingredients with a substantial proportion of tartaric acid tends to deposit tartrate crystals during the process of clearing, particularly in cold conditions. Such crystals can also be found in containers of grape juice concentrate and mistaken for sugar crystals. The process, known as tartrate stabilisation, is particularly important for white wine, which is usually served chilled. This is easily observed in a glass container but obviously not in a cask. Although harmless and tasteless, they are best removed from the cask with a hot solution of washing soda as they are insoluble in cold water and can be stubborn. I do this with carboys but as yet have not felt the need with casks.

It seems that the pin is proving popular with whiskey distillers. Not only is the size very easy to physically manage, but the whiskey matures faster. The same may apply to spirits in general.


written by Tony Hibbet

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