Wood and Maturation
Andrew Fitzgerald
28.08.20
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In 2013 Ben and I (may have) built a small still in my Carlton garage and (may have) started distilling whiskey. Initially just a hobby it was fun to create something from raw ingredients. Ben had been distilling in his home state of South Carolina since pre-teen years, I had really only ever drunk whiskey and besides a love for it, knew little about production. Over the months that followed, Ben taught me the basics of fermentation, distillation and eventually maturation.

The garage we worked in was small and the floor sloping with uneven pavers, which proved less than ideal, but did the job. We always had the roller door partly up when we would distil for ventilation. I had an incredibly nosey neighbour who’s driveway, oddly, always seemed to need sweeping whenever we were distilling. He would switch from broom to leaf blower, trying to steal a glance under the roller door just to see what we were up to. I am certain he thought we were cooking amphetamines.

We (may have) distilled a number of spirits from various grains including barley, rye and corn. We then matured a number of those distillates in a variety of ways. Firstly, in jars with oak staves inserted in them and later in small 5L barrels we purchased over the internet. This is where my love for maturation first kicked in. We had distillate, of varying volume in jars of varying volume with oak inserts of the same size. The speed of maturation and impact that the oak had on the whiskey simply based on with volume of whiskey or volume of air in the container was so varied it blew my mind. This seems so elementary to me nowadays but back then, as green as I was to the craft of whiskey making it was cool to see.

In 2015/2016 when we scaled to a ‘proper’ distillery, variation in maturation results continued, sometimes by design and other times because we used what barrels we could find. Whether it was the char level of the barrel or, oak type or even barrel size – the whiskey would age differently and inherently taste different. What we started to do is establish a foundation of experience – both through trial and research. Although both Ben and I come from engineering backgrounds, Ben has always been the more technical and scientific of the two of us (read: smarter). He is the one that is forever breaking out the calculator to run formulas. I am typically breaking out beers and running to the shop to buy a burger. But maturation intrigued me. So much so that I started to read articles about the science behind it.

Of interest to me initially was the impact of maturation in smaller barrels. Our cousins across the pond in Tasmania were favouring smaller barrels and often they promoted that they could produce great whiskey quicker with a number of them releasing Single Cask 50L barrels (at $220 + per bottle). The underlying concept of small barrel maturation is the Surface Area to Volume ratio of oak and whiskey. In simple terms, smaller the barrel, the greater ratio of oak to whiskey is. This makes sense, after all if the primary (extractive) objective of maturation is to improve the whiskey through compounds from the oak derived from the breakdown of lignin, then increasing the oak quantity will support that. My concerns with the trials we ran was the wildly inconsistent results and at times the over extraction of certain less favourable compounds rather than the more favourable. This could also be caused by the fact that the smaller barrels were often sourced by more ‘boutique’ cooperages and therefore quality and variety of oak used varied greatly. But I would suggest this is not the only cause.

Our focus for maturation was always to smooth and sweeten our whiskey. After all, we have long been influenced by American style whiskey – especially Rye. With rye, we start with a spicey and overtly dry distillate that the rye grain creates and from there we want to throw a blanket of sweetness over it. With the small barrels we often saw higher extraction of the drier sensory compounds which some studies suggest could be associated with Guaiacol or possibly Eugenol and cis-3-Methyl-4-octanolide. Although those compounds are important contributors to the flavour of whiskey, without a decent dose of Vanillin and other sweeter compounds it seemed unbalanced to us. ‘Grippy’ is a term often used around our tasting table to describe the often over extracted product. A number of variables could have been adjusted to modify the results we were seeing, like lowering ABV or utilising used oak, ideally from previous spirit maturation rather than wine as wine often extracts less and also different compounds than whiskey from the oak. One thing I did notice however is when the smaller barrels turned from tasting good to grippy, the smaller the barrel, the less time it would take to turn. It was a rapid descent.

We soon turned away from smaller barrels because in the long run we wanted to produce a consistent whiskey and not rely on ‘Single Cask’ releases for any other reason other than to celebrate an exceptional whiskey. We still have a few small barrels left in the racks, but these held spirit beforehand and so maturation is definitely not as rapid. It will be interesting to see them at a full 2 years.

My next focus to feed my curiosity was to look at Oak itself. The tree, the treatment and the finished barrel. During a trip to the US, I was visiting a distillery in Washington state and the head distiller there was telling me that they select trees from a Single forest as it sees less rain and therefore the tree’s rings were tighter and better suited to barrel production. My mind – blown. The concept of controlling the supply of barrels from forest through to distillery seemed like an impossible concept in Australia. My previous dealings with Cooperages were a bit – ‘you get what you get’. I mean, we have very skilled Coopers in Australia but even they can be limited in the wood that they source. The very idea that you can curate the barrel was a dream come true because what we had seen from our earlier barrel trials was inconsistency in barrel quality meant I could never set a ‘baseline’ to our maturation trials. Narrowing down the source of the oak was a logical step, but my research showed that even in the same forest, on the same hill the oak characteristics would alter greatly. Although it’s to be expected that barrels change (even with great QC) what we were initially getting from the smaller cooperages was like juggling with knives - it sounds cool but catch it by the wrong end and it will ruin your day. Some of the larger cooperages have managed to test the oak based on its chemical make-up and then group the oak into categories. Again, if consistency was our mission this was a good first step.

I sourced a number of barrels from different cooperages, all with the same specification on toast and char levels. What did vary was the forest the timber was sourced from and also the length of time in which the barrels were ‘seasoned’. Seasoning is the drying of the timber prior to processing. First the timber is cut into rough ‘blanks' and left stacked in the open to ‘season’ in the variable climate for 12, 18, 24 or 36 months depending on specification. Depending on where the Cooperage is located, they can see the rain, snow, wind and sun, and it is this process that leaches out some of the harsher tannins that would ultimately give the whiskey a harsh, astringent taste with an unseasoned timber. What we discovered in our cooperage/supplier trial was that oak seasoned for greater than 18 months certainly showed greater levels of the vanillin compared to the younger barrels. This qualitative assessment was supported by some lab tests provided by one of the cooperages that showed that the seasoning not only reduced water levels but decreased fatty acids, ketones and aldehydes in which that cooperage proposed contributed to the ‘green timber’ taste we could see in younger oak. The same lab study suggested that seasoning also promoted the Oxidation of ellagitannins which resulted in less astringency (the grippy tastes I referred to earlier). Starting to piece together the results we were seeing in the distillery and what I was reading in studies was a fun discovery.

After seasoning, how that oak was then coopered was certainly the next main contributor to variation, what I soon learned was ‘heavy toast’ may not be the same everywhere. And number 3 char at one cooperage may be a number 2 or number 4 elsewhere. Most of the distilleries I had visited in the US, which included some of the biggest in Kentucky used a number 3 or 4 char on their barrels. Ben would call this ‘alligator’ char. My concern with this level of char is mostly related to length of time the spirit is in the barrel. The process of maturation allows the spirits to enter/exit the oak fibres over time and progressively get deeper into the oak. My concern with the heavier char levels is that because we only intended to age between 2-4 years for the majority of our spirit, the spirit may only reach the char and not the sweet toasted oak below. This proved true in practice with a lot of the first barrels we filled were #4 char and we almost gave up on them after 2-3 years of maturation because they tasted bitter and over extracted. Those same barrels that are now reaching 4 years old are starting to taste delicious. Glad we never dumped them. But lighter char, heavier toast ended up being the sweet spot for us. We actually produce a certain percentage of higher char barrels so we can use them to ‘salt and pepper’ the blend as Ian (our production manager) would say. Which works exceptionally well.

To this day, we run constant R&D trials, in fact we are currently running a trial for the International Stave Company (ISC) out of Kentucky which has seen us fill a variety of barrels of varying specification with identical spirit. I am a long way from being ‘expert’ in maturation and are continually grateful that I have people like Ian Thorn and Ben Bowles around me that know the science and are keen to share that knowledge. I would say however, after all my reading and asking stupid questions, tasting a lot of whiskey in a lot of different barrel types has been the most informative journey. We now source 95% of our barrels from one cooperage with the 5% coming from another to offer some balance (salt and pepper). We now specify the temperature and length of time we want the barrels to be toasted for and we also identify the oak ‘profile’ and seasoning length. All these things are the result of countless hours drinking whiskey in the barrel house. A hard job but somebody has to do it.