Effect of Char Level on the Flavor Development
of Bourbon Whiskey
By Andrew Wiehebrink, R&D Spirits Division
Introduction
Charring an oak barrel is not only a preference for some spirit producers—in many cases, it is also a process mandated at the government level for specific beverage categories. The charring system ISC uses today is standardized across four different levels based on the amount of time the barrel is allowed to char. Char #1 represents the shortest length of charring, and then each level increases the duration, with Char #4 being the longest time allotted. This experiment explores the impact of different char levels on the flavor development of
barrel-aged spirits.
Objective
The purpose of this experiment is to examine the flavor differences that arise in bourbon whiskey by utilizing barrels with different char levels after four and a half years of aging in barrel.
Methods
Base Liquid
Variety: New make bourbon distillate
Mash Bill: 70% corn/20% rye/10% malted barley
Entry Proof: 115 proof/57.5% ABV
Trial Execution
Entry Date: June 2011
Primary Maturation Period: 55 months
Warehouse Location: Woodinville Distillery, Woodinville, WA
The Trial
New make bourbon distillate filled in the following barrels:
Four barrels of each variation were included in the experiment.
Samples were taken from each barrel at 55 months and then analyzed using Gas Chromatography-Mass Spectrometry (GCMS). All compound concentrations are displayed in graphs either as a percentage of the average concentration across all barrels in the experiment or concentration in mg/L.
Results and Discussion
Concentrations for eight key barrel flavor components are shown in Figure 1.1. Results demonstrate all char levels produced a similar overall flavor profile based on the extractive concentrations measured.
Figure 1.2 displays the total extractive concentration for each char level. Char #1 produced the highest concentrations over the 55-month period, closely followed by Char #2. As char level increased, the total extractive concentration decreased.
In the spirits industry, sweet aromas and flavors are of particular importance due to their overall positive reception by consumers of barrel-aged spirits. Figure 1.3 shows the difference in sweet flavor compound concentrations between the char levels, with Char #1 overall offering the highest amount compared to the other levels at 55 months. At this point in aging, Char #1 also offered the highest amount of vanillin, which is of note due to its desirable flavor and low threshold of perception.
Conclusions
This experiment showed all four char levels yielded a similar overall flavor profile by the end of the experiment. However, the data also demonstrated that lowering the char level increased the overall extractive concentration by boosting the concentration of sweet aroma and flavor compounds, such as vanillin and furfural.
Lower char levels may produce higher concentrations of oak extractives, especially compounds associated with sweetness, for several reasons:
- Thinner char layer – previous research indicates compounds can get trapped in the char layer of the barrel. By lowering the char level, we minimize the potential for favorable compounds to be retained within that charred layer by reducing its thickness.
- The nature of hemicellulose and lignin degradation – the majority of the compounds associated with sweet aromas and flavors typically do not hold up well to high temperatures. Heat is needed to create these compounds, but too much heat can have a negative effect on their concentrations. All four barrel char levels can offer a desirable variety and concentration of extractives, as evidenced by the similar overall flavor profile in this experiment. However, since the sweeter components are more sensitive to heat than the spicy or smoky components, with a less intense char, concentration of sweeter components should elevate.
Books are available through your account manager.