I was reading a study called “Chemical content and sensory changes of Oloroso Sherry wine when aged
with four different wood types”  and you can probably understand why this study is off particular interest to me. Just like the “Ex-Bourbon” cask is somehow seen as a “constant” within the whisky blogosphere, the “ex sherry” cask is also seen as a “constant”. Just to start this blog off with some insights.
There is no such thing as a “constant” “ex-bourbon cask” or a “constant” “ex-sherry cask”. Each cask is different.
Nothing to shocking about that statement, but it is good to get the no-brainers out of the way.
So why is the García-Moreno et.al study  so interesting? The study was intended to show that choice of origin of wood and toasting levels are options for producers of “Oloroso Sherry” to choose from to create flavour profiles.
“suitability of other types of woods for the ageing of these wines was carried out. To compare the characteristics of the alternative woods, an oloroso wine was aged in four groups of 16 L barrels made of French oak, Spanish oak, chestnut, as well as American oak as control, with intense and medium toasting. Phenolic and furanic compounds, organic acids, volatile compounds, color characteristics, total poly-phenol index and sensory analysis of wines aged for two months were analyzed. The results confirmed that the aged samples could be differentiated on the basis of their chemical composition, and that the use of alternative woods to age oloroso Sherry wines, and the level of wood toasting, had the potential to provide products with specific differences to the traditional aged in American oak. Furthermore, the organoleptic characteristics of these alternative wines were valued above a standard Sherry wine.”García-Moreno et.al 2021 
So this study took one initial product, matured it in casks made from 4 different kinds of wood, all same size, but with different toasting levels. Then looked at the differences between the 8 after a period of 2 months.
American oak (Quercus alba, AM), French oak (Quercus robur, FR), Spanish oak (Quercus pyrenaica, SP), and chestnut (Castanea sativa, CH)
One of the nice parts of the Abstract is the part where it is taken as a given that Oloroso Sherry is traditionally aged in American Oak. There is always much discussion in the whisky blogosphere about the oak used for sherry production.
The study also mentions what the difference is between en “medium” and a “intense” toast. I am not saying this is an industry standard, because there are no cross-industry standard for toasting and charr levels. The cooper, Tonelería J. L. Martínez, used: “For the intense toasting procedure, the cask had remained in an oven for 10 min–12 min at 130 ◦C–140 ◦C, the medium toasted barrels stayed in the oven for 5 min–7 min at a similar temperature.” quote from .
I find that interesting because whisky producers always mention “medium toast” without actually telling how that is done. It annoys me that this level of transparency is not provided. I can understand why no-one does though. Only nerds like me would want to know.
One line in the study also made me smile since it linked to a blog I have been meaning to make to debunk “angle share”. Anyways, here is the quote:
“Finally, the alcoholic strength of the samples increased slightly with ageing, perhaps due to evaporation phenomena because water molecule is smaller than ethanol molecule and therefore, it could penetrate better through the pores of the wood”García-Moreno et.al 2021 
I find that quote so interesting because it is stating the very very obvious. The water molecule is so much smaller than the ethanol molecule. If a cask is “air-tight” and “water-tight”, why would it not be “ethanol-tight”?
Anyways, I was going to write about the sensory differences between the 8 liquids.
Results of the study
The study clearly shows that different kinds of wood and different toasting levels result in different levels of congeners in 2 month old oloroso liquid. I selected some congeners in whisky that I know are of interest. Sorting the table on “Guaiacol” aka “Burnt / Smoky”  gives this overview. For the other congeners I gladly refer to my “Revised Scottish Whisky Flavour Wheel” page.
What does that mean for Whisky?
It means, again, that the origin and choices made by the original sherry producer result in different kinds of chemical make-up of the oloroso liquid. Choices that anyone buying actual “ex-sherry” casks for the whisky industry, which have been used in a solara for ages, needs to take into account and take an interest in.
It also means the i.e. “seasoned” casks used by MACALLAN would need to be very quality controlled in order to get a consistent product from cask too cask.
What this reconfirms for me is that there is no such thing as an “ex-sherry” cask. Just like there is no such thing as a “Standard cask” for the USA bourbon industry. You know the “ex-bourbon” cask. Anyone mentioning “ex-sherry” on their label is basically saying … well … you know … not so much.
It’s true still. Just as true as when I say that I drive a “Japanese Car”.
It also means that the blogpost I made earlier called “Oak Species Flavour Profiles“, which details a study by MARTÍNEZ ET. AL. 2018 , is right in saying the wood type is very important when maturing any drink or spirit.
I received feedback, by Ruben from “SherryNotes”, on the conclusions I made above. I missed an obvious thing. The choices that can be made by whisky makers are naturally limited to the casks currently available. If there are no Spanish or French oak cask available, that were actually in a solera system, then you can’t acquire them either.
In my mind it is already very obvious that different wood profiles result in different sherry profiles. But that doesn’t mean different wood profiles are actually used in the same way the study did.
 García-Moreno, M. Valme & Sánchez-Guillén, Manuel & Delgado-González, Manuel & Durán-Guerrero, Enrique & Rodríguez-Dodero, M. Carmen & García-Barroso, Carmelo & Guillén, Dominico. (2021). Chemical content and sensory changes of Oloroso Sherry wine when aged with four different wood types. LWT- Food Science and Technology. 140. 110706. 10.1016/j.lwt.2020.110706.
 Martínez Gil, Ana & Alamo-Sanza, Maria & Sánchez-Gómez, Rosario & Nevares, Ignacio. (2018). Different Woods in Cooperage for Oenology: A Review. Beverages. 4. 94. 10.3390/beverages4040094.
 K. -Y. Monica Lee, Alistair Paterson, John R. Piggott, Graeme D. Richardson, Origins of Flavour in Whiskies and a Revised Flavour Wheel: a Review, Journal of the Institute of Brewing, Volume 107, Issue 5, 2001, Pages 287-313