Varnished Barrels - Can we use them for Spirits?

Varnished Barrels - Can we use them for Spirits?

Published : 01-04-2020 - Categories : Home Distilling , Spirit Enhancement

We received a Facebook enquiry from a client two days ago, asking whether or not he could use a varnished barrel to age spirits in.


Our intuitive reacrion was NO. It cannot be done. And the reasons included the chances of Contamination – ethanol actually absorbing or dissolving some of the varnish into the spirit, reduced air and alcohol movement through the wood due to the wood being sealed, the reduction in the release of natural tannins from the wood, etc.


So we went looking for proof – an article, scientific paper, discussion, lecture … pretty much anything that can answer the question.


Surprisingly enough, we could find very little about it. 


Very few Barrel Suppliers mention varnish on their websites, mostly because most do not supply varnished barrels – which is no real surprise. Barrel suppliers that do mention varnished barrels are evenly split in two groups:


  • Those Barrel Suppliers that do supply varnished barrels, use it as a sales point that their barrels are varnished.
  • Those Barrel Suppliers that do no supply varnished barrels, use it as a sales point that their barrels are not varnished.


No real surprises there either. But the problem is that no-one is backing up there claims either way. Statements are made, but nowhere are these statements defended or supported.


Hence this article will try to explore the issue a little bit more in-depth.


What are the Common Perceptions about Varnished Barrels?


Many of the Distillers Forums and Social Media discussion Groups have touched on the topic of Varnished Barrels in the past, but for the most part people seem to be influenced or preconditioned to support the purchase choices they have already made.


Users of varnished barrels would say that they use them because:

  • My angel share is reduced
  • My barrel looks nicer
  • My barrel doesn’t get dirty or cleans easier
  • My barrel doesn’t mould
  • My barrel didn’t need to be sealed beforehand


Users of unvarnished barrels would say that they use them because:

  • My barrel breathes better, giving me more flavour
  • My barrel is functional, not decorative; hence I don’t care how it looks
  • My barrel is all natural, with no glues, varnish or chemicals that will affect my flavour


Even the professionals cannot seem to agree. 


Quoting from one article on how to care for barrels:

“Resist the urge to varnish your barrel. If a barrel is varnished the natural tannins that are released from the wood will be hindered. The oak flavours will be lost, and the spirits will be contaminated by the varnish.”


Another article states:

Some companies will put a varnish on the barrel. Our barrels that we sell are natural wood so there is no way varnish seep into the spirit or keeping the oak barrels from breathing.



There are no nails or screws, or glue used to assemble a proper barrel; rather, the wood staves fit together perfectly and are held in place simply by two metal hoops and pressure. Because distillers want the whisky to interact with the wood, there’s no varnish or sealant used anywhere on the barrel.


While on the other side of the spectrum we find maintenance instructions:

“Over time the exterior of your barrel will show wear. Lightly sand your barrel with a fine sandpaper. Wipe off any debris with a clean cloth and apply a coat of water-based varnish on the outside of the barrel.”


Sales and Marketing statements:

Our Premium Oak Barrels are fully finished with a water-based food grade stain and varnish and are available either Fully Charred or Toasted.


And then there is this one:

Wine and liquor will stain wood just like will stain carpet. Our barrels are varnished to decrease the chance of staining; however, gin will still stain.


NOTE: We have absolutely no idea why Gin specifically will stain a barrel – our only assumption here is that the author was referring to Bathtub Gin (Direct Infused) which has a colour. Possibly another area to research.


So, in the face of all this conflicting information, how do we make an informed decision? Let’s investigate.


What is Varnish?


Varnish is traditionally a combination of three ingredients: 

  1. a drying oil
  2. a resin
  3. a thinner or solvent


However, different types of varnish have different components. 


After being applied, the film-forming substances in varnishes either harden directly, as soon as the solvent has fully evaporated, or harden after evaporation of the solvent through a curing processes, primarily a chemical reaction between oils and oxygen from the air (autoxidation) and chemical reactions between the different components of the varnish.


  • Resin varnishes "dry" by evaporation of the solvent and harden almost immediately upon drying. 
  • Acrylic and waterborne varnishes "dry" upon evaporation of the water but will experience an extended curing period. 
  • Oil, polyurethane, and epoxy varnishes remain liquid even after evaporation of the solvent but quickly begin to cure, undergoing successive stages from liquid or syrupy, to tacky or sticky, to dry gummy, to "dry to the touch", to hard.


Now, here is the kicker: Originally, alcohol or turpentine was used to dissolve the resin and thin the drying oils. It was also used to clean brushes and clothes used to apply the varnish, hence yes – alcohol can dissolve varnish.


Will Varnish contaminate my Spirits?


As ethanol can dissolve varnish, it is extremely possible that varnish can contaminate spirits. But it seems to depend on the type of Varnish used.


A quick bit of online research shows us that the basic categories of varnish (and their ethanol solubility) are:


Resin Ethanol Soluble
Shellac Ethanol Soluble
Alkyd Solvent Resistant
Marine (Spar) Probably Soluble (normally Resin Based)
Drying Oils Ethanol Soluble
Polyurethane Sometimes Ethanol Soluble
Lacquer Not Ethanol Soluble
Acrylic Ethanol Soluble
Epoxy Sometimes Ethanol Soluble
Conversion Toxic (gives off Formaldehyde)

In contrast though, a thread on a Woodworking Forum yielded the following information:


Fully cured drying oil finishes, except ones with zinc (and other metallic) driers, are usually suitable to come into contact with food. The FDA regulates this in the US, these so-called food grade finishes are usually made from tung oil (china wood oil is another name). You will see FDA approved on the label of the product. Mineral oil is what you often see. It is not a drying oil. IMO it is a very poor wood finish. Most water-based finishes have molecules that are emulsified and are not water-soluble. When the water evaporates the polymers form - acrylics or products like Hydrocote work okay with this application. These water-based finishes are kind of like drying oils in disguise. "Varnish" is kind of non-specific. It can be oil, water-based, and even catalysed.


NOTE: The above FDA reference does not specifically refer to barrels, but to worktops, counters, cutting boards, etc.


So, the short answer seems to be that most varnishes can contaminate your spirits, but not necessarily all of them.


Will Varnish change how my Barrel Works?


Can air pass through varnish?


You would think that should be an easy question to answer. You would think so but be very wrong. Not if your definition of an answer is an article or research paper or peer reviewed statement giving a categorical Yes or No answer.


What is abundantly clear however, is that people that work with varnish are very careful about the application of varnish unto wood to stop the formation of bubbles inside the varnish. Even insofar it applies to the methods of stirring the varnish. 


Base on the ability of Varnish to trap air, it is therefore reasonable to assume that air cannot pass through the varnish.


Now why is this at all important? Is that not a good thing? Does that not mean we will reduce losses and limit the Angel Share?


Oxygen is one of the most reactive agents on the planet.


It is generally responsible for all rust and corrosion you see about you. Some 21% of our atmosphere is composed of it. And of course, we breath it. It aids us in breaking down these complex molecules, but in doing so also affects our ethanol. And so, it works best to expose our distillate to very minute amounts of oxygen slowly.


A Wooden barrel does this brilliantly. It is porous enough to allow a slow exchange of gases while being solid enough to contain liquids. Over time, a transpiration of gases occurs where much of the more complex compounds, including unfortunately, quite a bit of ethanol, evaporate out of the barrel. Oxygen slowly migrates into the barrel.


This form of "respiration" is influenced by temperature changes. During the day, as the liquid contents heat, it tends to migrate gases out of the barrel and the liquid expands deep into the pores of the wood. At night, as the contents cool, they contract creating a bit of a vacuum which allows more external gases to be absorbed by the wood through the exterior walls.


In this way, our barrel breathes. 


Seasonal changes affect this heavy breathing as well. Often, especially in the past, barrels were stored in high humidity areas with stable temperatures such as caves, and in modern times, in cellars. This slows the process. At the other extreme, they may be stored in tropical warehouses, with open sides, which tends to increase the activity.


The very air around the barrel storage ultimately effects the flavour of the product. Many Scottish whisky makers located on the shore tout the sea-salt air as a significant flavour component. This may overstate the case, but indeed the air is part of the native terroire of their whisky and is one of many variables making one whisky different from another.

Just some of the benefits of this slow Oxygenation include:


  • Colour is stabilized from oxidation of free anthocyanins and the condensation of tannins.
  • Tannins soften due to polymerization 
  • Precipitation reduces astringency in the final product


Especially when working with Charred Barrels, Oxygenation becomes very important.


The process that turns our plain distillate, into a smooth bourbon or whisky with undertones of vanilla and caramel happens inside the barrel, when clear distillate is introduced to oak – normally charred oak in the case of Bourbon.


Charring – amongst other things - breaks down the lignin in the wood into organic compounds called aldehydes. These are the main building blocks of maturation. When you add alcohol to the barrel, oxidation transforms the aldehydes into acids - syringic acid (from syringaldehyde), ferulic acid (from coniferaldehyde), and vanillic acid (from vanillin). 


During the aging process, changes in heat and pressure push and pull the alcohol in and out of the wood – a process called transpiration (more on that just now). There is a constant back-and-forth between aldehyde and acid, until the acids accumulate en masse and turn permanently into esters, adding complex character and deep flavours.


Now, if air cannot pass through varnished wood, it is most certain that liquid cannot pass through either. This means that during barrel aging, transpiration cannot occur.


As we just touched on, transpiration is the process of spirits moving in and out of the wood, or even through the wood. This process occurs in a regular barrel due to the osmotic pressure changing on the outside of the barrel relative to the inside of the barrel. Fluctuations in exterior temperature and humidity can cause these changes, and lead to greater transpiration.


As a Varnish does not allow Oxygenation or Transpiration to take place, a spirit product placed in a Varnished Barrel will not benefit from these processes.


NOTE: We did speak to an expert in Wood, Wood Processing and Wood Treatment to confirm whether or not our assumption of Varnish not letting the Barrel breathe is correct. He stated that if Oils are used (that would fall under the Drying Oils category discussed above) the wood would still breathe. However, as we’ve established, there is a fairly good chance that those oils would be Ethanol Soluble, and therefore you would probably get contamination. Again – we must be mindful that there are MANY different products on the market, and this may not always be the case.


So, what is the answer – Yes or No to Varnished Barrels?


Because the term “Varnish” is so widely used – and sometimes incorrectly used – it is incorrect to say that ALL varnished barrels will be dangerous or contaminate the spirit.


What IS however abundantly clear is that a Varnished barrel will NOT work the same as an unvarnished barrel, and therefore it is safe to say that the statements from suppliers that the barrels are the same is false.


We are awaiting feedback from two Cooperages and a Laboratory that advises the Wine and Spirits Industry on safe chemicals and compounds to use, so hopefully we will be able to expand on this article in the near future.

At Distillique, we will continue selling only unvarnished barrels, until we have conclusive evidence that specific types of varnishes, does not impair maturation in barrels. 

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