Two step maturation process experiment

[sid_marx]

Hi, I make whiskey at home, and whilst I do enjoy drinking the new make, I’m mostly interested in producing an aged product.
I’ve tried glass with chips, dominos and spirals and for the most part I don’t feel like it results in a final product that I want to drink.
Having said that one of my batches that rested on a combination of lightly toasted seasoned oak dominos + Jack Daniel’s barrel chips for about 2 years was drinkable.
I also have a number of Badmo barrels, the oldest of which I filled in August ’22 (about 19 months ago at this point) and I feel like the product in the Badmos is streets ahead of the product in glass - albeit not quite ready to drink yet.
I keep my Badmo barrels in an uninsulated ceiling cavity to take advantage of the big daily temperature swings in helping the maturation process along. My assumption is that the temperature swings exaggerate the pressure differential between the inside of the barrel and the environment, thus accelerating both extraction and gas turnover (and oxygenation) in the barrel via the porous barrel head. I also assume that the high temperatures on sunny days speed up the chemical reactions taking place in the barrel.
So I’m happy with the progress of my barrelled product.
However, I have a limited number of Badmos, so they represent the key constraint in my production system.
To compensate I’m also maturing product in beer kegs on various oak pieces including light and medium toasted dominoes, barrel chips & toasted, charred staves from Badmo. My intention is that this part forms the 1st step in a 2 part process, which I consider to be the “extraction” step. The idea being that when a Badmo barrel becomes free I’ll decanted from one of the kegs into the now-second-use Badmo barrel for an “oxygenation” step of probably 12-24 months, which will be the second step in the process.
I have a relatively high level of confidence in this plan, but I’m also considering variation of step 1 to help speed the whole process along.
Here’s what I’m planning.
Each keg is 19l, currently my kegs have approximately 18l of product (including the oak) and 1l of headspace. When I taste the product from the kegs I’m pretty happy with the flavour from the extraction but can tell that the effects of oxygen (and time) are lagging. 
I have a hypothesis that if I can induce evaporation through the exchange of air in the keg at a rate similar to that experienced in full sized barrels, that by proxy, I’ll achieve at least some of the benefits of oxidation/micro-oxidisation in the keg.
Working on the assumption that standard oak barrels lose somewhere in the region of 2-5% of their volume per annum via evaporation (with humidity determining whether more ethanol or more water is lost in the process).
So I’m planing on initially targeting at 1.5ml daily rate of evaporation for my kegs, which approximates the full size barrel evaporation when scaled.
The mechanism for this is to be by forcing compressed air (clean air via a hand pump) through the dip tube (and possibly through an aeration stone attached to the dip tube).
I’d initially do this daily and would release the pressure via the PRV each day before adding a perhaps a litre or so of air (to begin with).
The way I’d dial in to my evaporation target is by weighing the keg weekly, looking for a drop of approximately 10.5 grams per week and adjusting the air turnover around that target.
Prior to staring this I’ll take about a litre of product out of the keg so that I can conduct periodic side-by-side tasting to see whether or not my hypothesis is proving out.
Keen to know if anyone has done similar experiments or whether someone can spot flaws in the rationale underpinning this experiment.

[NZChris]

You don't give any details on how you age in glass. If you are not trying to emulate the amount of air exchange that occurs in a barrel, don't expect the same results. Putting a tight lid on a full demijohn is probably the worst place to start when wanting to age in glass.

Expecting to replicate ten year old product in a couple of years is very likely going to disappoint unless you do some fast aging trickery.

[Tōtōchtin]

One thing that might help you since you're in kegs is using an oiless pump. You can use the pump to create pressure and vacuum in the kegs. You would also be adding oxygen when you pressurized the keg.
Tōtō

[sid_marx]

NZCHris, Here's more detail on my previous glass method for clarity: 2.2l fully sealed glass jars with 1/5th to 1/3rd headspace, opened approximately once every 6 weeks for tasting and gas turnover. So probably insufficient oxygen exposure. Maybe I need to try a method for allowing a low level of continuous gas exchange with my jars, perhaps the method Jessie on Still-it has mentioned a few times - the PTFE tape wrapped gasket method.

I'd be stoked to replicate an 8 year aged product in 6 years with my experimental 2 stage keg+badmo process, maybe that's unreasonable, maybe its achievable!

I'm also considering trying a slightly loose oak bung in a 25l keg for the keg stage.

Tōtō, That sounds cool, I've gone super lo-fi with the pump, its a garden spray pump (unused) with a gas post connection.

[Tōtōchtin]

With an oilless air pump you could create a rickhouse by pushing the ethanol into the wood then pull it out with a vacuum. Aerate the liquid as you're pressurizing the keg
Hope find what you want.
Tōtō

[sid_marx]

Tōtō, your suggestion has piqued my interest, particularly in considering the differences between ageing in barrels and kegs. I've been operating under the assumption that, within a keg, the oak is both fully submerged in the spirit and saturated, leaving little room for the traditional expansion and contraction process that drives spirit into and out of the wood in barrels. Since the oak is saturated, it wouldn't contain air pockets to compress or expand, making it less likely for an internal change in pressure to significantly impact the liquid's interaction with the wood in the same way barrel ageing does.

However, your idea about the pressurisation-depressurisation cycle led me to consider another aspect - the effect on dissolved gases. Creating a vacuum might encourage dissolved gases within the spirit to come out of solution, potentially bubbling out. This process could not only facilitate micro-oxygenation by allowing new gases to dissolve into the liquid during subsequent pressurisation but also might contribute to the overall maturation process by simulating some of the oxidative effects seen in barrel ageing.

This opens up interesting possibilities for enhancing the ageing process through controlled pressure changes, even in a system where wood interaction is primarily through submerged and saturated oak.

[sid_marx]

I think I'll try the pressure cycling idea. I can use this hand pump which has both inflate and deflate capability to create the vacuum in the keg, and the other pump to create the pressure. I'll probably start with a 2 day cycle: 1 day under pressure, 1 day under vacuum. Bearing in mind that the spirit in the keg has been on oak for 18 months at this point, so I figure the "extraction" step is well along its path and this is going to be more about oxidation effects. Specifically I'm hoping this process might promote the formation and acids and aldehydes through oxidation of the alcohols. This could open up the possibility of esterification and trans-esterification reactions introducing new flavour compounds, adding complexity and depth to the whiskey. My hope is that the oxidation of higher alcohols and the esterification of the resulting acids may also help to mellow the spirit out and give it a smoother, rounder mouthfeel. I'll probably do an initial 7 day trial of this and then give it a taste vs the control sample, which I've already removed from the keg.

[sid_marx]

No discernable difference (to my palate) between the pressure cycled and the control after a week. I'll reduce the cycle to once a week and taste again in a couple of months.

[JustinNZ]

Just briefly back to glass aging: a coffee filter does a great job as a gasket in clip-top jars (y’know, wire and glass tops). In a 5L jar over two years I lost exactly 10% of the alcohol to the angels. Acceptable loss and very clear product change - for the better. Over and out.

[NormandieStill]

Just briefly back to glass aging: a coffee filter does a great job as a gasket in clip-top jars (y’know, wire and glass tops). In a 5L jar over two years I lost exactly 10% of the alcohol to the angels. Acceptable loss and very clear product change - for the better. Over and out.

Thanks for that. I'm currently ageing almost exclusively in swingtop jars like that. From 1.5L all the way to 5L.

Bleached or unbleached? And at what sort of temp do you keep them?

[JustinNZ]

I don’t know about the paper used. Faggs is the brand though. I just have the jars at room temp inside, so roughly 15 to 25 deg C all year round. I’m just a simple time, oak and a little bit of air guy. Probably cos I’m lazy.

[sid_marx]

Thanks for the coffee filter tip JustinNZ, I'll give that a go on some of my jars.