The yeast used for fermentation in the distillation process is not too dissimilar to beer brewing yeast, and brewing yeast can often be a suitable substitute for distillers yeast. The goal for the yeast in both beer fermentation and distilling fermentation is the same; they both need to produce reasonable quantities of alcohol in a manageable timeframe, settle out of solution and produce low levels of off flavours.
If you do decide to try a specific distiller’s yeast you should be looking for a yeast that uses a heat tolerant Alpha Amylase for converting the complex starch into sugar during the boil stage and also importantly that contain Amyloglucosidase Enzyme, that converts long chain sugars left over from the mash into fermentable glucose.
Many spirits use spices and botanicals to give the spirit unique characteristics that are specific but not limited to that spirit, like juniper berries in gin, cinnamon in cinnamon whiskey and vanilla in spiced rums. Botanical infusions are incorporated into spirits in a couple of different ways;
Vapour infusion: is the process of combining the spirit with the spices and botanicals by using equipment to place the botanicals and spices in contact with the alcoholic vapour as it boils off the wash before the condenser. The botanicals and spices can also be placed in line with the distillation process after the condenser, so the liquid alcohol flows over the botanicals or spices before getting to the collection vessel.
Steeped: Botanicals or spices can be steeped in several ways including in the wash, before the distillation occurs. However, even though the flavour can carry over from the distillation if the spices or botanicals are left in the wash during the distillation, their bitterness or unwanted flavours can also be carried across and the spices and botanicals are boiled during the distillation, which is not always desireable. Botanicals and spices can be steeped during the ageing process before the spirits are bottled, or the botanicals and spices can be steeped in the finished bottle. Both these latter methods are more commonly found in a home brewing circumstance.
Many spirits like whiskey, bourbon and brandy are generally aged with wood that impart both flavours and colour from the wood to the spirit. These woods impart different flavours and colour depending on the type of wood and how the wood is treated before coming in contact with the spirit. The spirit is aged on the wood until the distiller decides the right amount of flavour has been added to the spirit. The speed in which this occurs depends on the climate the spirit is being aged and the way the spirit is being aged, e.g. using barrels (large or small), wood staves, chips or spirals.
As you could imagine, a plethora of wood types exist and as such the variety of flavours they can impart is also vast. Here are a few of the more commonly used wood types for whiskey, bourbon and brandies;
American oak: Quercus Alba is the type of white oak most commonly grown in the United States. The forests in Minnesota and Wisconsin are considered particularly good sources of oak. American oak is sweeter and contains more vanillin compounds than other oak species. American oak tends to impart more obvious, stronger and sweeter aromas and flavours. Common descriptors for American oak as well as vanilla are coconut, sweet spices and dill.
French oak: Quercus Petraea and Quercus Robur are the two species of white oak grown in France. Of the two Quercus Petraea is considered the finer. The most important oak forests in France are Allier, Nevers and Tronçais (all in central France), the Vosges in the northeast, and Limousin, which is more westerly near the Cognac region. Of the five, Limousin is the only forest to grow Quercus Robur. French oak (particularly Quercus Petraea) is much tighter grained and less dense than the American Quercus Alba. As such French oak imparts more subtle flavours and firmer, but silkier tannins.
Toasted and Charred oak: These can be either American or French oak that is toasted and or charred using ovens or open flame to draw out particular flavours out the wood.