For garnishing, it depends on the garnish as discussed below. It’s not uncommon to mix and match garnishes! A lot of people like both an onion and olive in a Gibson or olive and twist in a Martini.
Twists are normally the zest of lemon, but you can use any citrus: pink grapefruit and orange are also used but much more rarely.
A twist is about 1 square inch per 50ml of drink – or about the size of a coin. As a normal Martini is ~100ml, a twist is usually about 2 square inches or 2 coins. This is just a guide - nothing says you can’t use more or less though.
Use a vegetable or potato peeler on a lemon’s zest, and peel it from one end to the other. Try not to press so hard that you get pith (the white flesh under the zest) when peeling, though not always possible to do. If your twist has a lot of pith, it’s best not to put it in the drink, as it’s extremely bitter and it will affect the Martini.
Once you have your zest, express the oils (squeeze the zest) over the Martini so you get tiny droplets of zest oils floating on the top of the drink. Then gently rub the rim of the glass with the peel. You want the drink to smell of citrus.
‘Twisting’ doesn’t do anything to flavour, just decoration, as the oils will have been expressed. However, the twist is traditionally then twisted (initially, wrap it around a straw or bar spoon to get it really twisted like a spring, while doing it by hand takes a bit of practice) and placed into the drink, but sometimes discarded.
It’s your preference whether it’s in the drink or not, but remember if there’s a lot of pith, it’s best discarded.
Simply put one or three (never two!) good quality pitted olives (from brine) on a cocktail stick, and place it into the drink.
If making a Dirty Martini, also take a bar spoon or two of the brine and add it to the drink.
Simply put a pickled silverskin onion on a cocktail stick and place it into the drink. Try to get onions that are pickled in a white wine vinegar, as then the vinegar and vermouth are both made from the same base liquid. It’s actually both the vinegar together with the onion that makes Gibsons interesting, not just the onion.
If you pickle the onions yourself, make sure neither vinegar nor onion comes into contact with steel (like the blade of a knife or jar cap) – use a ceramic knife and glass container, as vinegar is extremely corrosive with iron. The vinegar’s flavour will be ruined, the knife will be severely blunted and the onion becomes mushy – they should be crunchy.
If you make a lot of Gibsons, we strongly recommend you pickle your own onions, as shop-bought pickled onions have to be pasteurised and this affects flavour.
There is also a 'Burnt' Martini, by adding a spoon or so of very peated and smoky Scotch whisky (usually an Islay Single Malt) to your Martini.
It’s not uncommon to garnish Martinis with other ingredients. Cocktail Bitters such as Angostura, Celery and Orange are very common. Another example, if using a coastal gin often works much better by adding some sea salt rather than a twist. Some types of bark (e.g. fig tree bark) also work wonderfully, particularly with earthy, umami gins.