Whisky, worts and all

Ian Wisniewski asks, why do some distilleries have clear wort and some have cloudy wort, and what significance can this have?
By Ian Wisniewski
The usual conclusion is that cloudy wort promotes a richer style of new make spirit, compared to clear giving a lighter, fruitier spirit. This conclusion therefore suggests that the nature of the wort (ie the sugary liquid that drains from the mash tun) is a definitive factor. That would be very convenient, but it's also too simplistic. The nature of the wort is only a subtle influence, and just one of several factors which together determine the character of the new make spirit.These other factors include the size and shape of the stills, the type of condensers, and the spirit cut.

Slimmer, taller stills for example, promote lighter, fruitier new make spirit than rounder, shorter stills. Similarly, the more modern shell and tube condensers encourage a lighter spirit than worms, which are the more traditional type. Meanwhile, the spirit cut can also select lighter, fruitier characteristics and avoid richer, heavier notes. Consequently, these factors can mitigate, or override the influence of the wort, which means that its nature doesn’t in itself guarantee the character of the new make spirit.

This brings us to the question of what makes the wort clear or cloudy, which is the level of fine particles suspended within the liquid. This in turn takes us back to the milling process at each distillery.

Milling the malt (ie grinding it through rollers) produces three different grades of malt, known as husk, grits (or ‘middles,’ ie. medium ground), and flour (or ‘fines,’ which is ground much finer).

A typical milling specification is 20 per cent husk, 70 per cent grits, and 10 per cent flour, which provides an optimum surface area to extract the maximum amount of sugar during mashing (when adding hot water converts starches into sugars). It’s essentially the percentage of flour that accounts for the level of fine particles that make wort cloudy.

However, higher levels of flour don’t automatically promote cloudiness. That’s because the way the mash tun is operated also helps to determine whether the wort is clear or cloudy.

An initial consideration is the amount of stirring during mashing, using ‘arms’ that rotate around the mash tun. A certain amount of stirring is unavoidable, in order to promote drainage through the bed. This in turn ensures the optimum sugar extraction during a certain time frame, with every distillery subject to a strict production schedule.

Meanwhile, batches of malt delivered to a distillery can vary in terms of ‘processability’ (ie. the way they behave during production), and some may require more stirring. Consequently, distillery managers must evaluate how much stirring each particular batch requires. Minimal stirring at the slowest speed promotes a clear wort, while a greater amount of stirring means more particles becoming suspended in the liquid, and so, generally, cloudier.

Another factor is the rate of drainage during mashing. This depends (among other factors) on the size of the holes in the plates at the bottom of the mash tun, through which the wort drains.

Once the wort has drained from the mash tun and been pumped to the washbacks (fermentation vessels), yeast is added to begin fermentation. This is also the stage when the clear versus cloudy debate becomes even more interesting, as each type of wort behaves differently during fermentation.

‘You tend to find that if you’ve got some cloudiness in the wort there are more specific nutrients that the yeast can feed on, so you tend to get a slightly faster fermentation. If you don’t control this you can possibly get too high a temperature too soon and the yeast can expire (before converting all the sugars).

“So, you can control this by lowering the pitching temperature and rate (ie. the amount of yeast added),’ says Dennis Watson, technical and scientific affairs director at Chivas Bros.

The type of wort used also determines the level of foam produced during fermentation, which highlights the role of the switcher blade.

Resembling a propellor, this is positioned at the top of the washback in order to cut through and reduce the level of foam.

The level of fine particles in the wash (ie fermented wort) also raises another issue, which is the risk of these solids adhering, or even burning onto the heating elements in the wash still.

This may seem a practicality, but the consequences can be significant.

‘When yeast bakes onto hot still or heating surfaces this may promote yeasty, caramel type flavours, but any cereal residues baking on it can lead to other flavours, with a cereal and/or bitter note.

“Clearly this baking on also affects the efficiency of the heating surfaces, affecting the rate of distillation, and, in extreme cases, this can affect the consistency of spirit quality.

“This only applies to the wash stills, as solids do not carry over, and causes the wash stills to require cleaning more often,’ says Dr Bill Crilly, technical support manager at The Edrington Group.

Whether a distillery produces clear or cloudy wort is down to tradition. Whatever the influence may be on new make spirit at each distillery, no manager wants to see a batch of cloudy wort if clear is the norm, or vice-versa.

This would be a sign that something’s gone wrong which needs to be corrected.