Tank aging of fruit/berry based Liqueurs

[Still At It]

Hi everyone,

We make a black currant Liqueur.  We ferment the fruit, add brandy, and our sweetener.  We are now on batch three, and find that our batch one has a slightly deeper flavor. One big difference is that it rested in stainless for almost 3 months before bottling where as batch two had virtually no time in tank. I’ve tried to find some the science behind ageing in stainless tanks but I am coming up short. I know that Time in stainless tanks does alter the spirit but I don’t fully appreciate how and therefore I don’t know how long I should be doing it, if I should be doing it or if it is complete Hocus pocus.   If this has been already discussed, please quickly toward that Thread however I was unable to find this exact answer! I appreciate any and all comments that this conversation generates!

Thank you,

 

Jeremiah 

 

[Silk City Distillers]

It comes up anecdotally here, people note improvements in flavor or aroma due to extended holding times.  Interestingly, it seems to apply to both holding in tanks as well as holding in bottles, so perhaps it's time that's the important factor and not necessarily the vessel.  It also doesn't appear to be specific to a spirit, heck I've even seen references to vatting vodka, which when you think about it, should be largely irrelevant.  Probably the same phenomenon, or at least related, is the negative impact to the product from proofing/processing/bottling (bottle shock).  Tasting from a just-bottled bottle, for me, seems to taste much thinner, flatter, and devoid of aroma, and even a few days time results in pretty marked improvement.

It can't be as simple as oxidation, otherwise it would be relatively easy to just inject oxygen to speed the process and improve quality.  There is lots of discussion about the formation or disruption of micelles and other factors related to the physical structure of specific chemical compounds in the spirit, including some  phenomenon associated with the speed of proofing (and it's potential reversal over time). 

If you are looking for the smoking gun, sorry.  But at the same time, it's clearly not just hocus pokus.

In your process though, using a fermented product as input, there are a host of potential batch-to-batch variations there, don't overlook the input either.

[Foreshot]

 @MDH You're really good with the chemistry of spirits. What are your thoughts?

[PeteB]

I recall a presentation at an ADI conference in Louisville about 5 years ago. A researcher from Tuthilltown was giving great detail about "molecular clustering" of ethanol. Over a period of time the molecules attract to each other and form clumps that trigger a more mellow sensation on the tongue.

That presentation was about ethanol only, maybe other flavour compounds clump as well.

[princeofpancake]

Was the container sealed? Any sort of evaporation will throw off your flavor profile and make the flavors more concentrated.

[Oregon Spirit Distillers]

I would be concerned with oxidation from the head space causing color/flavor changes with the fruit.  You can fill the head space with CO2 or other gas to prevent this.

[RobertS]

Operating theory for holding vodka before bottling for me has been degassing volatiles into the head space. Even with no air transfer, trace volatiles and minimal ethanol enter the head space due to vapor pressure and are left behind when transferring to another tank or bottles. Bottles have less head space and are more likely to have it shook back in shortly before opening.