What to Use for Cocktail Aging

1. Barrels: Traditionally used for spirits, these wooden vessels impart nuanced flavors to cocktails, adding layers of woodiness, vanilla, or charred notes. Most bartenders use miniature casks rather than traditional spirits barrels (which can be expensive and cumbersome). The smaller the barrel, the faster and more intense the effect. If you want an aged cocktail for a competition next week or have a high turnover in a busy bar, consider using 5-liter barrels.  
2. Glass Bottles: Offering a neutral aging environment, bottles allow the cocktail components to meld without the influence of wood. Small glass bottles can also be used for single-serve cocktails or larger bottles for decanting.  
3. Stainless Steel Containers: They are used for cocktails where neither the influence of wood nor glass is desired, providing a purely integrated flavor profile. 

Cocktail Aging: Techniques and Best Practices

1. Select Ingredients with Care: Aging a poorly made cocktail is not going to make it better. Use reasonable ingredients and make it with the outcome in mind. If you aim to add a lot of sweet flavors from a small bourbon barrel, for example, it might pay to make the drink a little drier. Don't age anything that will go off; old dairy or rotting fruit juices aren't going to do you any favors.

2. Choose the Right Container: Barrels offer wood-infused complexity, while glass and steel provide a more neutral ground for ingredient interplay. If the alcohol beverage volume (ABV) of the drink isn't high enough, wines and vermouths can oxidize to acetic acid in the same way an open bottle of wine goes sour in a few days. In this case, an airtight bottle might be a good bet. 

3. Aging Duration: Unlike spirits that might age for decades, cocktails usually mature over weeks or months. Regular tasting is essential to determine the optimal aging period.

4. Rotation: If using barrels, periodic rotation ensures even exposure to the cocktail, promoting uniform flavor development.

5. Storage Conditions: Consistent temperature and limited light exposure are crucial. Cellars or dark storage areas are ideal. If you buy new barrels, ensure they aren't lined with lacquer or treated with (potentially toxic) wood preservatives. They need to be of food-safe quality. 

Aging’s Role in Contemporary Mixology 

Cocktail aging has carved a unique niche in the modern bar scene:   

• Signature Barrel-Aged Cocktails: Establishments age house-special cocktails in barrels, presenting patrons with unique, matured versions of classic concoctions.  
• Bottle-Aged Classics: Negronis, Manhattans, and other stalwarts, when bottle-aged, offer a softer, more integrated drinking experience.  
• Aging with Wood Chips: Mixologists infuse cocktails with toasted wood chips for an accelerated aging effect, imparting a barrel-aged character in less time.  
• Aged Cocktail Menus: Some bars offer exclusive menus featuring aged variants of popular drinks, providing patrons with familiar yet evolved taste experiences.