I did a previous experiment using heavy toasted French and American oak on a cider to see if we could recognize a difference in the aromas. This led to using oak more often and to even start experimenting with different wood, like maple, hickory, and birch. Wood is a great adjunct for cider. Besides adding aromas, it can also impact the acids and the phenolic compounds. Most research on aging with oak is done on wines and in barrels. However, I found some research using oak chips in cider. W. Fan and associates explored the impact of French, American, and Chinese oak at different toast levels (light, medium, and heavy) on a cider(1). The results are pretty interesting.
First, let’s explore the impact that aging on oak can have to compounds that provide key organoleptic characteristics like aroma and taste. As the below table highlights, esters are increased, alcohols are reduced, and acids are increased. Since esters are formed when acids and alcohols combine, it highlights the impact oak can have. We might expect esters to increase and both ethanol and acids to go down. We see alcohols declining but acids are actually increasing. That indicates that the oak must be contributing compounds with the likely candidates being acids that react with the available alcohols. There is also a marked increase in oak aromas like vanillin. It was noted that American oak had the highest concentrations of vanillin of the three oaks tested.
Impact of Oak on Key Compounds
The next assessment was on how the toast level (light, medium, or heavy) of the oak impacted the key compounds in the cider. W. Fan and associates used French Oak for this assessment. While oak increases the amount of total esters, the level of toast didn’t have a big impact on the amount of esters. We also see a decline in total alcohols and an increase in the total acids. The outlier appears to be the heavy toasted sample. The esters increased the most while the alcohols decreased the least and the acid level were comparable to the control sample. However, W. Fan and associates found that the medium toasted sample contained the most oak derived volatile compounds while the heavy toasted version saw signifiant increases in 3-Methylbutyl acetate, Ethyl hexanoate, and Ethyl octanoate. This indicates that the burning or toasting of the wood is impacting the type and level of compounds released.
Impact of Toast Level on Key Compounds
The other variation that was assessed by W. Fan and associates was the amount and time of maturation with oak. As you might expect, the more you add, the more bigger the impact. Also, the longer you age the cider with the oak, the bigger the impact. There are some interesting aspects related to the amount of oak added. Like the level of toasting, the esters increase as more oak is added. The alcohols decrease but the level of decrease reduced as the amount increases. This same pattern holds for the decrease in the amount of acids. One of the findings was that certain compounds are more readily released while others steadily increase. They also found that the type of oak can impact the release of compounds. While more vanillin was found in American oak, the French oak releases the vanillin faster. They recommended 4 grams per liter of oak for 40 days. However, I’d suggest you use that as a starting point and experiment.
Impact of Amount of Oak on Key Compounds
|Control||2 g/l||4 g/l||8 g/l|
Overall, this research didn’t note much difference between American and French oak but definitely differences between these and Chinese oak. My personal experience indicates that as with most aspect of cider making, this is often an individual preference. We personally noted some differences between American and French oak and I have liked the impact from heavy toasted oak over medium toasts. Either way, oak is one of my favorite adjuncts for hard cider as I believe it can help smooth an acidic cider by adding the perception of sweetness and add complexity to a cider lacking aromas and balance. It is an easy to add adjunct that can often help improve almost any cider.
(1) W. Fan and associates, Influence of Oak Chips GeographicalOrigin, Toast Level, Dosage and Aging Time on Volatile Compounds of Apple Cider, Journal of the Institute of Brewing, 112, 3, 2006
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