Page 104 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

b. Justify the methods used to recycle A and G.

c. What unit operations do you suggest for your separators? Justify your choices.

d. How would your PFD change if the price of feed material G were very low?

How is Scotch whisky made?

The following descriptions of malt and grain whisky manufacturing are given here courtesy of the
University of Edinburgh at http://www.dcs.ed.ac.uk/home/jhb/whisky/swa/chap3.html. For each of
the two processes, sketch a process flow diagram.
15.

There are two kinds of Scotch whisky: malt whisky, which is made by the pot still process, and grain
whisky, which is made by the patent still (or Coffey still) process. Malt whisky is made from malted
barley only, whereas grain whisky is made from malted barley together with unmalted barley and
other cereals.

Malt Whisky

The pot still process by which malt whisky is made may be divided into four main stages: malting,
mashing, fermentation, and distillation.
(1) Malting
The barley is first screened to remove any foreign matter and then soaked for two or three days in
tanks of water known as steeps. After this it is spread out on a concrete floor known as the malting

floor and allowed to germinate. Germination may take from 8 to 12 days depending on the season of
the year, the quality of the barley used, and other factors. During germination the barley secretes the
enzyme diastase, which makes the starch in the barley soluble, thus preparing it for conversion into
sugar. Throughout this period the barley must be turned at regular intervals to control the temperature
and rate of germination.
At the appropriate moment germination is stopped by drying the malted barley or green malt in the
malt kiln. More usually nowadays malting is carried out in Saladin boxes or in drum maltings, in
both of which the process is controlled mechanically. Instead of germinating on the distillery floor,
the grain is contained in large rectangular boxes (Saladin) or in large cylindrical drums.
Temperature is controlled by blowing air at selected temperatures upward through the germinating
grain, which is turned mechanically. A recent development caused by the rapid expansion of the
Scotch whisky industry is for distilleries to obtain their malt from centralized maltings that supply a
number of distilleries, thereby enabling the malting process to be carried out more economically.

(2) Mashing
The dried malt is ground in a mill, and the grist, as it is now called, is mixed with hot water in a
large circular vessel called a mash tun. The soluble starch is thus converted into a sugary liquid
known as wort. This is drawn off from the mash tun, and the solids remaining are removed for use as
cattle food.
(3) Fermentation
After cooling, the wort is passed into large vessels holding anything from 9,000 to 45,000 liters of
liquid, where it is fermented by the addition of yeast. The living yeast attacks the sugar in the wort