As each stage of the production process entails options that influence the character of the new make spirit, every decision is significant.While the focus tends to be on the size and shape of the stills, and perhaps the length of the fermentation process, one essential decision is the type of washbacks used for fermentation, either wooden or stainless steel.Wooden washbacks raise the issue of what type of wood to use, larch or pine, with Oregon pine and Douglas Fir the two names used when discussing pine.However,both names refer to the same type of tree, which grows in North America.And while both names have been used in the past, Douglas Fir has become established as the standard reference,because this is the name used by timber suppliers.A key difference between both types of wood is that larch has more knots, and a looser grain than pine.“More knots in the wood means more chance of a leak, but even with knots larch is very durable.Larch is Scottish grown,”says Ron Low, proprietor of Joseph Brown Vats of Dufftown.Beyond the choice of wood, the size and capacity of a washback is determined by practicality, in order to streamline the production process, with one washback typically accommodating the contents of one mash tun.Constructing a wooden washback begins with assembling planks for the base.“I take off one eighth of an inch on each side in order to clean the planks, which gets them down to two and three quarter inches.Then, laid out on trestles we join each plank so they’re all flush,and put in dowel holes followed by the dowels, as no nails are used.We sand this circular base with a floor sander, to avoid any steps in the joins.Then the base is taken apart and we chamfer the edge on the underside with a hand plane, taking off a quarter of an inch to create the cantle,onto which the staves are placed,”says Ron Low.Staves are prepared by putting them through a machine that puts a convex and concave contour on each (convex on the outside).“If it’s a straight-sided vat we look at the angle and it’s quite straightforward. If it’s tapered we take the top and bottom diameters and work out the difference,and when we’re jointing, the staves would need to be wider at the bottom.Once the staves are all jointed, and you’ve counted all your measurements, you cut a groove called a croze in every stave, to get it attached to the base, then the hoop sits over the croze and holds it together,” adds Ron.However, the final stage takes place at the distillery rather than the workshop.“We flatpack and build the washback on site.The depth of the washback determines the amount of hoops, usually 15-16 hoops.We take the measurement for the first hoop, which is joined by rivets,we have a hydraulic punch, put rivets through, then flatten the rivets.Hoops are made from galvanized mild steel, which gives a bit more stretch than stainless steel. Each hoop is hammered down, which brings the staves together.The time taken, from measuring each hoop to riveting and getting it into position, is around one and a half to two hours,depending on the size of the vat,”says Ron.Once constructed further preparations are required before a washback can be used for fermentation.Once the engineers have completed the pipe work, the washback is slowly filled, adding a little more water each day,until it reaches the top.Although time consuming, this approach achieves a vital objective.“This sees a slow swell in the wood, which is best, with our original measurements allowing for a certain amount of swell.Meanwhile, there’s a bit of leakage for a couple of days, then after the wood has swollen, which closes any remaining gaps, the washback is steam cleaned,”says Ron.Constructing a washback is a process that obviously requires experience and expertise.But also time.“Putting together a washback we usually need up to two weeks in the workshop, and one week on site,”adds Ron.Meanwhile, a similar schedule is used for stainless steel.“Making an average size stainless steel washback takes three guys about three weeks.Washbacks for most malt distilleries can be completed at our works and transported in one piece. Larger washbacks are taken to the site and welded together, which could take four to five weeks on site, the larger the washback the longer it takes,”says Richard Forsyth of Forsyth’s.Producing stainless steel washbacks, which essentially date from the mid 1970s,begins with stainless steel sheets.“The shell is made from rectangular stainless steel sheets, cut to the required circumference.Twenty sheets may be required, with four meters by two meters a typical size for a sheet, though you can also get sheets measuring six meters by two meters.The seam is visible where joined,though internally there is a smooth finish,” says Richard.Once completed, the maintenance required is one aspect of comparing wooden and stainless steel washbacks.“Wooden washbacks have an average life-cycle of around 30 years. I also do maintenance and inspections for distilleries during the silent season, looking for leaks, rust build-up behind the hoops, soft rotten timber,woodworm and mis-shaping,”says Ron Low.Russell Anderson of Highland Park adds,“We have a total of 12 wooden washbacks and are in the middle of replacing one washback a year,having started the process five years ago.”As the distillery is part of The Edrington Group, an inhouse cooperage team includes four employees that are building Highland Park’s Douglas Fir washbacks.By comparison,“Stainless steel washbacks are virtually maintenance free, and built for life.It’s a very resilient metal, with no wear,”adds Richard.Cleaning wooden washbacks also requires more effort than stainless steel, with an essential difference being that stainless steel washbacks provide a virtually sterile environment,whereas wood can’t (whatever the cleaning regime).This results in wooden washbacks having a higher level of microflora (bacterial presence) than stainless steel.Another practical factor is that steam is used during the cleaning regime for wooden and stainless steel washbacks, which entails a cooling down period after cleaning.“As you add yeast as soon as possible after adding wort, you don’t want to pump wort onto a hot surface.Distillery operators check the temperature of the wort in the washback before they add yeast. It wouldn’t change the wort if it was too hot, only the yeast could be affected, and yeast cells could be killed,”says Derek Sinclair of Inver House.A subsequent question is whether washbacks made from larch have any individual influence on fermentation compared to Douglas Fir?“I believe you get similar fermentation efficiency regardless of the type of wood washbacks are constructed from,”says Stuart Robertson of Springbank, with Springbank and Glengyle both having larch washbacks.But how about any differences in terms of the manner in which fermentation takes place, and the characteristics of the resulting wash, when using larch compared to Douglas Fir?“I believe it makes a difference as larch has a tight grain and smooth surface,whereas Douglas Fir has a slightly more open grain and rougher surface.Therefore it stands to reason that even after sterilisation there could possibly be a higher bacterial count at the start of fermentation in the washback with a more open rough surface.This will have an influence on the resultant wash as there will be an increase in the acidity due to the bacterial activity,”adds Stuart Robertson of Springbank.Meanwhile, comparing the influence of wooden to stainless steel washbacks raises various related issues.“As stainless steel is a virtually sterile environment you get a very clean fermentation so you maximise the volatile,sweet, fruity compounds and get a very clean character.With Glenmorangie the level of the most volatile esters, that give stimulating aromas, is maximised.This is in conjunction with a shorter fermentation, whereas a longer fermentation period potentially allows these to diminish,”says Rachel Barrie of Glenmorangie.“Through the natural microflora present in wooden washbacks I’d expect to see more long chain fatty acid esters, which contribute more to texture than aroma,and you’re more likely to build up heavier, richer compounds.That’s down to a combination of wooden washbacks and longer fermentation.Wood has more of an insulating effect on the level of acidity during fermentation, so wooden washbacks tend to take longer to ferment than stainless steel,”adds Rachel Barrie, with Ardbeg having Oregon Pine washbacks.