The Anatomy of a Penicillin

The smoky Scotch cocktail has been deemed a modern classic. Tyler Zielinski analyses the key characteristics that helped encourage the drink's rapid rise to the top and asks the experts how to make the perfect Penicillin

Words by Tyler Zielinski

Penicillin cocktail header

In his 2016 book, A Proper Drink, award-winning cocktail writer Robert Simonson calls the Penicillin ‘the most well-travelled and renowned new cocktail of the 21st century.’ Simonson’s take is assertive, but the man speaks the truth. Since its creation by bartender Sam Ross in 2005, the Penicillin, a perfectly balanced and compelling blend of two Scotches, ginger and honey syrups, plus fresh lemon juice has gone from strength to strength. From the hallowed grounds of Milk & Honey in New York City where the drink originated, the gingery and smoky Scotch sour spread like wildfire to cocktail bars around the world, quickly establishing itself as a bona fide modern classic.

While Ross seeded the Penicillin – his twist on the Gold Rush, the drink’s predecessor made with bourbon, honey syrup and lemon juice – at many of the US bars he consulted for in the following years, the cocktail migrated across the pond by way of Milk & Honey’s satellite bar in London. ‘I remember writing the autumn-winter menu for Milk & Honey [London] in 2006, and by that time we had already long-since received the Penicillin recipe from Sasha [Petraske, the bar’s late founder],’ says Kevin Armstrong, owner of London bar Satan’s Whiskers and former bar manager for the Match Bar Group, which Milk & Honey was a part of. ‘The Penicillin itself was clearly a world-class recipe and needed no help in its propagation stateside, but in terms of traction in the UK, Milk & Honey was instrumental in the speed at which the cocktail became recognised and picked up by bartenders in London.’ 

bartender making penicillin cocktail
The Penicillin was invented in 2005 by bartender Sam Ross at Milk & Honey in New York

The main difference between the Penicillin served in the States compared to the one in London was, and is, the unit of measurement. Instead of imperial ounces, London bartenders mixed in millilitres – a subtle change, but it caused the rest of the cocktail’s recipe to be recalibrated in order to properly balance everything. Nonetheless, both versions of the Penicillin employed Milk & Honey’s standard specifications for the ginger and honey syrups, called for the same whiskies, and were mixed using the same method. But as the temperamental sour strayed from the Milk & Honey family, the Penicillin became adulterated with subpar syrups and ingredients, losing its precision.

‘If you change the base spirit, you should also change the proportion of the honey, ginger and citrus,’ says Adam Hussein, food and beverage supervisor at the NoMad Hotel London, and author of Rise of the Bartender. ‘It isn’t as easy as a straight swap.’

From how the syrups are made and the proportions of each ingredient, to the specific whiskies and ice used to craft the cocktail, every single detail makes a difference when it comes to crafting the perfect Penicillin. To get to the bottom of this modern classic, we’ve asked a handful of experts to weigh-in on the subject.

Penicillin cocktail
A bona fide modern classic, the Penicillin is a blend of two Scotches, ginger and honey syrups plus fresh lemon juice [Image: Till Britz]

The sweet and sour

At the heart of this cocktail is the quality of its ginger and honey syrups. In the Penicillin, the ginger syrup not only aids in the dilution and body of the cocktail – in tandem with the honey syrup – but it also contributes a spice which adds depth of flavour and a sensational mouthfeel, putting the cocktail up a peg from the standard sour. The key to having a snappy ginger syrup is using fresh ginger juice, and balancing it accordingly.

‘You should juice the ginger with a high-speed juicer,’ says Hussein. ‘Then gently heat the ginger juice and slowly add demerara sugar (equal in weight to the amount of ginger juice) until fully dissolved.’ 

At Satan’s Whiskers, Armstrong opts for a 1:1 ginger syrup using caster sugar instead of demerara. It’s a subtle difference, but yields a slightly less viscous product. The most important detail is balancing the intensity of the ginger’s spice with the sugar.

The most important detail is balancing the intensity of the ginger’s spice

As for the honey syrup, in addition to being one of the sweeteners to balance the citrus, this component is key in binding all of the ingredients together and giving the Penicillin a medium-bodied mouthfeel and delicate froth that makes the cocktail shine. While Satan’s Whiskers opts for a 2:1 ratio, examples at NoMad and Attaboy – Sam Ross’ bar which exists in the old Milk & Honey space in New York – call for a richer 3:1 ratio, resulting in a more viscous Penicillin with a longer finish (my personal preference).

Putting the sweet and sour components together, they should generally be matched at a 1:1 ratio, with an equal split of honey syrup and ginger syrup to lemon juice. ‘If you’re using a different and more intense honey syrup, or you like to use a less sweet ginger syrup, then you’re going to need to adjust the rest of the recipe,’ Armstrong says. ‘And if you’re thinking about swapping the fresh ginger syrup for a ginger-based liqueur, you’ll likely end up with a drink that’s a long way from where you wanted it to be.’

penicillin cocktail no garnish
Depending on the strength of each component of a Penicillin, the other flavours will need balancing

The whiskies

Ross’ touch of brilliance wasn’t the use of the blended Scotch for the base, but the float of smoky Islay whisky. ‘The joy of the Penicillin for me is that unadulterated and undiluted hit of peated whisky that accompanies the first few sips,’ says Armstrong. ‘The extra dimension offered is like the overproof rum float on a good rum cocktail, or the thick layer of cold heavy cream that makes the Irish Coffee so compelling.’

Leon Wilkes Back, head of mixology at Virgin Hotels Edinburgh, ditches the float and adds the peated whisky in the shaken base mixture. I believe this combines everything together for a more balanced profile of the flavours,’ says Wilkes Back. ‘However, as a nod back to tradition and to ensure that the aroma of the drink is still the true smell of Scotland, we aromatise the cocktail with heavily-peated Islay just before serving it to the guest.’ It’s one example of how the Penicillin’s flavours have been slightly adapted in various bars around the world.

Virgin Hotels Edinburgh Penicillin cocktail
Leon Wilkes Back, head of mixology at Virgin Hotels Edinburgh makes a Penicillin

As for the specific whiskies called for in a Penicillin, this is where imbibers will find the greatest variances. Since the cocktail’s creation in 2005, certain whiskies have come and gone, while other products have steadily increased in price, eliminating them from the bartender’s toolkit altogether. ‘For over 15 years we only ever made our Penicillins with Compass Box Asyla as the blended whisky component and Lagavulin 16 year as the floated peated whisky,’ says Armstrong. ‘But when Asyla was discontinued, we moved on to Dewar’s 12 year; and with the price of Lagavulin 16 year increasing dramatically these past few years, we’ve shifted to Compass Box Peat Monster to replace this component also.’

At the NoMad Hotel, Chivas 12 year is the standard blended Scotch used in its Penicillin, while Hussein also offers up Johnnie Walker Green Label as a satisfactory base spirit. And at Commons Club at Virgin Hotels Edinburgh, Monkey Shoulder is the go-to blended Scotch with Laphroaig 10 year serving as the heavily-peated aromatic whisky.

‘In terms of the ABV, I think 40% is perfect for the base whisky,’ Armstrong notes. ‘If you’ve tried making a Penicillin with a much stronger base product, while the result is still excellent, the drink can become overwhelmingly big. Big on flavour, big on ABV and big on mouthfeel. Sometimes you can have too much of a good thing.’

penicillin cocktail with ice cubes
Ice is a hugely important factor when it comes to making a Penicillin

The ice

As far as the Penicillin is concerned, there’s ice to shake with and ice to serve with. Both make a substantial difference in the perceived flavour and texture of the cocktail. 

‘I think ice choice for shaking is integral,’ says Armstrong. ‘I spent some time in Little Branch with Sasha [Petraske] making a good number of other recipes, and his preference then was to shake with lump ice. When doing this there is a noticeable gain in visible texture and foam, but large lumps of ice are not as effective at chilling and diluting a cocktail as an equivalent weight of good 1×1 cubes. Without the additional water that’s added through shaking with cubes, I find that the final product — even when the recipe is executed perfectly — can be thick, rich, and almost syrupy.’

The solution? Agitator cubes. To get the Penicillin to its optimal temperature and dilution without shaking for days, add one large tempered ice cube to a shaker with one or two 1×1 cubes of ice, and shake. The result is a frothy, properly diluted and chilled Penicillin that is arguably superior to all other shaking methods. 

Floating Islay Scotch over one large ice cube creates a more consistent drinking experience, starting with a pop of peaty smoke and finishing with a zing of citrus and ginger spice

But ice at service matters, too. At Milk & Honey, the Penicillin was always poured over a large, perfectly-cut cube of clear ice. It’s a preference of Hussein’s as well – but Armstrong has ditched the king cubes for standard 1×1 cubes at Satan’s Whiskers, and Commons Club has its own slant too. ‘We serve our Penicillin over chunks of what I refer to in the bar as service ice,’ says Wilkes Back. Instead of 1×1 cubes, or one large cube of ice, large chunks of clear ice are broken up from a block. Using this ice properly chills the cocktail just as well as one large cube, but manages the dilution more slowly than 1×1 cubes. 

To each their own, but serving over a large cube does give a flat surface upon which the peated Scotch can be floated. This even surface creates a more consistent drinking experience, starting with a pop of peaty smoke and finishing with a zing of citrus and ginger spice. It’s a subtle detail, but one that Petraske undoubtedly intended.

Penicillin recipes from the experts

Penicillin (adapted Milk & Honey New York recipe)

  • 60 ml (2 oz) Monkey Shoulder blended Scotch whisky
  • 22.2 ml (¾ oz) lemon juice
  • 11.1 ml (⅜ oz) honey syrup (3:1)
  • 11.1ml (⅜ oz) ginger syrup (4:3 fresh ginger juice to sugar)
  • 7.5 ml (¼ oz) Laphroaig 10 year Islay Scotch whisky (to float)

Method: Add all ingredients (except Islay Scotch) to a shaker, then vigorously shake with one large tempered cube and an agitator cube (i.e 1×1 ice cube). Strain the mix over a large ice cube into a rocks glass, float the Islay Scotch over the large cube using the back of a bar spoon, and garnish with candied ginger.

Satan’s Whiskers Penicillin

  • 50ml Dewar’s 12yr
  • 25ml fresh lemon juice
  • 12.5ml ginger syrup
  • 12.5ml honey syrup
  • 10ml Compass Box Peat Monster

Method: Add all ingredients (except Islay Scotch) to a shaker, then vigorously shake with standard bar ice. Strain the mix over 1×1 ice cubes into a 12 oz rocks glass, float the Islay Scotch over the large cube using the back of a bar spoon, and garnish with candied ginger and a lemon wedge.