Burning whisky barrel staves

Are barrel staves good firewood?

Are whisky barrel staves good firewood?

The short answer is yes, but not straight from the distillery yard.

When milling Oak for barrel staves the blanks are specified as the very best oak, so they are arguably the best species for burning to start with. However, staves from the whisky industry are not kiln dried so, although they are seasoned to a point, the locked in moisture is very much still present. This means they will burn but not efficiently enough due to the level of internal moisture, and they will burn 'dirty' as they emit acrid steam. There is also the chance of insects and larvae being present if they haven't been kiln dried.

Barrels are filled with liquid obviously and stored in dark still conditions, after use the staves are stacked uncovered outside in tight stacks so do not get chance to dry out properly. A fresh barrel stave can seem dry but still contains cellular locked in water in the Oak, which can be as much as 30% or more in the centre. So yes they are a great fuel but need to be dried first or they will produce less heat and excessive steam in your smoker / log burner / pizza oven. As with all wood fuel you can air dry them to a suitable level eventually, but kiln drying will consistently get them a lot drier. If this takes place in a modern biomass kiln this is an environmentally friendly fuel and also utilises a waste product.

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Why kiln dry wood fuel?

When fuel burns the heat it creates is absorbed by the water present in the wood as it turns to steam. This is why wet wood doesn't burn and kiln dried wood burns hotter than seasoned wood. To test moisture content properly you can either weigh it and compare to oven dried samples or split and test on the sides and in the middle with probes, the average of the values give you the moisture content.

We ran several tests for the whisky industry. We evaluated the following products from barrel staves:

1. Pizza oven mini logs for portable pizza ovens & basic firewood - excellent results

2. Smoking chips, shavings and dust for the kettle BBQ and smoker market - excellent results

3. Natural charcoal for BBQ’s or for use in filtering - not suitable for premium charcoal, results pending for whisky filtering

4. Biochar for soil improvement and carbon capture - excellent results

5. Craft blanks - interesting results, the best being sandblasted staves which look like driftwood, lots of possibilities.

6. Compressed heat logs - excellent results 

Preparation for all barrel stave products

The sample staves were between 25 and 32% moisture content in the centre which exceeds all maximum tolerances for any type of firewood or feedstock for environmentally friendly charcoal production. Although not illegal in Scotland yet (it is in England) the environmental downside of burning / selling wet wood is very well documented. Staves must be dried to below a 20% average moisture content before any of the target applications.

We processed some staves into short lengths and a crate of staves into long lengths to test efficiency and the efficacy of our kiln in both situations. Staves going into the kiln tested between 25% and 32% moisture content in the centre.

On taking the staves out of the kiln they were retested and measured a consistent 8 to 12% MC across the batch after 4 days at 60 to 70 degrees Centigrade. This makes them legal to sell for burning and ideal for turning into charcoal and biochar efficiently.

Making charcoal and biochar

We did a small test in the charcoal retort with end sections (lower moisture content) but the results were unsatisfactory. The charcoal delaminated, produced a lot of smoke and sparks, failed in places and was inconsistent. We concluded that the high moisture content requires the staves to be kiln dried before further processing for all products. Without kiln drying the staves emitted too much steam for the hydrocarbons to ignite and sustain a stable flare.

On testing with kiln dried staves (8 - 12%) we had far better results. The 'fire' in the video below is the kiln self feulling with syngas (hydrocarbons) held in the barrel staves flaring to burn off greenhouse gases and produce the high temperatures required for eco friendly charcoal and biochar production. 

Whisky barrel cooking charcoal

Once the staves were kiln dried we managed to produce a very pure batch of charcoal with no brown ends. Although it burned very hot and lasted a good amount of time, the staves (being quarter sawn) delaminate along the planes of the fibres and spark a lot so were sub optimal for use as barbecue charcoal.

Mixing with potato starch to make charcoal briquettes would make a longer, smoother burning product that would store and transport better but it would involve more complicated production, limiting the environmental benefits and greatly increasing the cost.

The 'fire' in the video is the kiln self feulling with syngas held in the barrel staves flaring to produce the high temperatures required for eco friendly charcoal and biochar production.

Whisky barrel pizza oven logs / hot smoker chunks

We took kiln dried staves and processed them through our smallest kindling machine. These worked extremely well, they burn really hot and produce a delicate whisky / smoky smell and flavour. Having a high auto ignition point, the Oak worked very well in offset smokers as well. We used an Ooni professional for testing. A local pub cooked 12 pizzas for us and the results were excellent, rapidly reaching the target temperature and holding it efficiently.

Whisky barrel stave mini logs
Mini pizza oven logs, kilon dried and ready for action


Cold smoker dust and whisky smoker chips

For cold smokers we collected the fine dust that is produced during processing, crucially after kiln drying then dried it further in the sawdust dryer. This is used in cold smoker environments for foods that do not require heat (cheese, fish etc). It is important for the dust to be very fine. Coarser dust and shavings worked ok for hot smoker boxes that are used in a kettle BBQ but we didn’t think this warranted keeping it as a potential product as the woodchip was better. The kiln dried fine dust worked extremely well in a ProQ cold smoker unit with salmon.

Again once kiln dried the waste parts of the staves processed through the chipper into small chips worked very well and are versatile in that they can be used in almost any outdoor cooking application.

Environmentally both are good because we are collecting a waste product created by processing another waste product, and being in the central belt of Scotland it hasn’t had to travel far from it’s source.

Biochar from whisky barrel staves

This is the most environmentally friendly way to repurpose waste barrel staves. The process sequesters carbon while flaring off the greenhouse gas, once mixed into soil the biochar locks carbon back in the ground for potentially hundreds of years. Biochar incorporation into soil is an important route for CO 2 removal from the atmosphere by terrestrial carbon sequestration. It also acts as a ‘home’ for beneficial microbes and bacteria which improves soil fertility and nutrient retention. It should be produced in a modern retort kiln in order to gain the most environmental gains, in the video above you will see the syngas (plentiful in whisky barrel staves) which self-fuels the majority of the cycle.

Biochar is also known as horticultural charcoal which is granular natural charcoal used to improve soil tilth and retain nutrients and fertiliser in the soil. There are various studies underway (including those by Edinburgh University and the EU) into using biochar as an important weapon to combat climate change and increase carbon capture.

Biochar can be sold via garden centres and online to the home garden / organic growers market. In theory, if we just carbonised all redundant staves into biochar and simply buried it, this alone would substantially reduce the industry’s carbon footprint.

Whisky barrel staves for making heat logs

Oak is very high in natural lignin which makes for an excellent binder when making heat briquettes for burning domestically. Following a great many tests in three different machines we settled on a process that produces a good mix of 1mm - 8mm particles dried to 8 - 12% moisture content then compressed without additives in a briquette press that has uses a double compression system and a potentiometer which creates a very hard, dense briquette.

The machine achieves a dry density of up to 900kg per cbm which is greater than oak's original density, packing a huge amount of energy into a small area. The result was the best quality briquette we have ever produced or used, we extensively field tested the product with our firewood customers and received what we expected which was 100% positive. The briquettes are extremely compact and burn very hot and clean.

Being pure oak, double dried / compressed using the correct particle blend the briquettes are clean and solid which also prevents them from reabsorbing too much moisture. This in turn means there is no need to use plastic for packaging, which we would not do in any case.  

Whisky Oak briquettes
High energy, compact heat briquettes made from barrels