Quality Oak
At Tonelería Murúa, we craft STR barrels (Shaved, Toasted and Recharred) from premium oak and barrels previously used for wine, applying a meticulous process of shaving, toasting and thermal renewal that reactivates the wood for a new ageing cycle. This treatment brings aromatic complexity, smoothness and balance to spirits and special wines, extending the lifespan of each barrel and providing a technical, sustainable solution tailored to the needs of every client.
An STR barrel is an oak barrel that has undergone a specific renewal process for reuse in ageing spirits. The term STR stands for Shaved, Toasted and Recharred, a process popularised by Dr. Jim Swan. It has become an effective and sustainable solution to extend the lifespan of barrels and optimise their ability to influence the aromatic profile of spirits.
Thanks to the STR process, a barrel previously used for wine ageing can add new layers of complexity to whisky, rum, brandy or other spirits. The result is active, balanced wood that combines sweet oak, vanilla, caramel or nutty notes, depending on the level of toasting applied.
Shaving is the first step of the STR process. It involves mechanically removing the inner layer of the barrel using specialised tools (such as an adze or technical sanding). This inner layer is typically saturated from its previous use (usually in wine ageing), and removing it exposes a new, active oak surface.
Shaving a barrel serves several purposes:
Eliminating residual tartrates, tannins and depleted compounds.
Preparing the wood for a new toasting phase.
Reactivating the oak’s pores to facilitate aroma transfer.
This process extends the useful life of the barrel and ensures a new cycle of use with more predictable behaviour during spirit ageing.
Once shaved, the barrel moves on to the toasting phase, where heat is applied to the inner surface of the staves. This step is key to shaping the sensory profile the barrel will impart to the spirit. The fire caramelises the wood’s natural sugars and generates a range of desirable aromatic compounds.
At Tonelería Murúa, we offer a wide range of toast levels, tailored to different goals:
For ageing whisky, rum or brandy, we offer four levels of CHAR toasting, each with a distinct impact on the spirit’s profile:
CHAR 1: Short and light toast. Adds soft vanilla and caramel notes. Although it is the lightest level for spirits, it is more intense than the highest toasting level used for wine.
CHAR 2: Deeper heat penetration into the wood. Toasted aromas intensify, with sweet spice and nutty notes emerging.
CHAR 3: Deep toast that intensively caramelises the wood’s sugars. Brings out cocoa, coffee and toffee notes, and promotes more active oxygenation.
CHAR 4 (Alligator Skin): The highest level. The inner surface is fully charred, creating a distinctive texture resembling alligator skin. This layer acts as a natural filter, softening the spirit and delivering great aromatic complexity with smoky and sweet nuances.
Each level is applied based on the type of spirit, ageing time and desired sensory profile. Our master coopers work on each barrel individually to ensure precision and consistency.
We offer a complete range of toasts, from natural to heavy, tailored to different wine styles and oenological goals. Each level affects tannin load, aromatic profile and mouthfeel differently:
Natural Toast: Wood with no heat treatment and minimal aromatic contribution. Ideal for preserving freshness and enhancing the wine’s fruit expression from early stages such as fermentation.
Light Toast: Low-temperature, long-duration toasting. Adds structure, balsamic notes and fresh wood aromas, enhancing primary fruit aromas without masking them.
Medium Toast: Balanced toasting that offers greater volume, complexity and spiced notes. Aromatic profile includes vanilla, nuts and roasted almond.
Heavy Toast: Designed with high thermal peaks to encourage the formation of compounds such as furfurals and volatile phenols. Gives the wine cocoa, coffee and smoky notes, along with a slight increase in sweetness on the palate. While this is the highest level for wine, it is still less aggressive than CHAR 1 for spirits.
Thermal renewal is the final step in the STR process. It consists of reheating the inside of the barrel after shaving and toasting, reactivating the oak’s chemical structure and creating a new functional layer. This heating can include light charring (rechar) for certain applications, especially in spirits.
During this stage:
The oak’s internal structure is stabilised.
New porous channels are created to promote controlled oxygenation.
Residual moisture and possible contaminants are removed.
Thanks to this renewal, the barrel gains a new “useful life” without the need for virgin wood. This represents a sustainable, cost-effective and efficient solution for producers aiming to maintain high quality standards without compromising the environment.
Thanks to the shaving and toasting process, the barrel regains its aromatic potential, quickly transferring notes of vanilla, caramel, spices or dried fruits. Ideal for young spirits seeking sensory richness in just a few months.
STR barrels reactivate the wood, although they will never be exactly like a new barrel. The result is a smoother integration between wood and alcohol, without aggressive notes and with a refined character tailored to each spirit profile.
Reusing barrels through the STR process reduces the demand for virgin oak and extends the lifespan of each unit. It is an environmentally friendly solution that combines performance, quality and a commitment to sustainability.
CHAR toasting is a type of controlled charring applied to the inside of the barrel, especially in the production of spirits such as whisky or rum. It involves exposing the wood to an intense flame for a set period of time, creating a charred layer whose depth varies depending on the level (CHAR 1 to CHAR 4). This treatment enhances the formation of aromatic compounds such as vanilla, caramel and spices, and also acts as a natural filter, softening the spirit and adding complexity.
Shaving is the scraping of the staves’ inner surface to remove residues and reopen the wood’s pores, allowing the barrel to contribute aromas in a second useful life. It is the first step in the STR process.
The type and level of toast (light, medium, heavy or CHAR) determine the aromatic profile the barrel will impart to the spirit or wine, ranging from spiced and vanilla notes to smoky and caramel nuances.
Barrel toasting can last between 20 and 60 minutes, depending on the desired intensity and the barrel’s final use. At Tonelería Murúa, we carefully adjust the time, temperature and type of heat for each case. However, converting an ex-wine barrel into an STR barrel involves several preliminary steps—such as repairing broken staves, checking thickness, removing the heads, and more—all of which take considerably longer than the toasting itself.
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