Maire O’Sullivan and Brian Nation outline how Midleton Distillery doubled capacity without altering the quality of the distillates, while also reducing energy requirements per litre of pure alcohol by 20%


Authors: Brian Nation, master distiller, Irish Distillers Pernod Ricard and Maire O’Sullivan, senior process engineer, DPS Engineering

Irish Distillers Pernod Ricard, in Midleton, is the home of Jameson Irish Whiskey and a number of other well-known brands such as Paddy, Midleton Powers and the single Pot Still range Red Breast, Green Spot and Barry Crockett legacy. There has been a great tradition of distilling in Midleton since 1825 when the Old Midleton Distillery, which is now a visitor centre, was opened. The current distillery opened in 1975 as a result of the amalgamation of the Powers, Jameson and Cork Distilling Companies. The distillery in Midleton produces the components for all Irish Distillers’ brands.

As a result of the continued success and growth across the globe of the Irish whiskey category, driven particularly by the success of Jameson, there was a requirement to double the size of the distillery at Midleton. A total investment of €200 million has seen the installation of new brewing equipment, new distillation equipment and a new warehouse facility.

The expansion gave Irish Distillers the opportunity to embrace new technologies in brewing and distilling with a view to reducing energy and water usage on the site. The main objective, however, was to double the capacity of the distillery from 33.5mlas (million litres of alcohol) to 64mlas without impacting the quality or taste of the final spirit.

Midleton brewhouse and stillhouses

The first stage of the expansion was to install a new pot brewhouse. This is where a mixture of malted barley and unmalted barley is milled, mixed with water and heated to different temperatures to convert the starch in the grain to fermentable sugars using the natural enzymes of the malt. This involved a change in brewing technology moving from lauter tun to mash filters.

Lauter-tun technology was the traditional way of draining the sugary rich solution from the grains. This was mainly done by gravity, whereas a mash filter is newer technology used for this separation but this is done under pressure. This decision was not taken lightly and involved a great deal of R&D before the final decision was made. The move to mash-filter technology enabled us to increase our yield from our cereal by circa 8%, i.e. to get more litres of alcohol per dry tonne of grain used. It also led to a reduction in water usage at the brewing stage of approximately 10%.

Once the brewhouse was installed and commissioned, we moved onto the garden stillhouse. The stillhouse is where the fermented material from the pot brewing is distilled three times in copper pot stills to produce pot distillate at circa 84.5% abv (alcohol by volume). This involved the installation of three copper pot stills, identical to the existing ones we had in the Barry Crockett still house. These pot stills have a volume of 75,000 litres each, making them the biggest operational pot stills in the world.

The pot stills needed to be identical in order to ensure that the quality and flavour of the final spirit did not change. Changing the volume or shape of a pot still can alter both the exposure of the vapour to copper and also reduce or increase the amount of reflux in the pot. We made use of thermal vapour recovery technology (TVR) on the condensers on the pots in order to recover one third of the steam requirement to run each pot.

The column stillhouse is where the fermented material from the low-temperature brewing process is distilled in three columns to produce a grain distillate with a strength of 94.4%abv. Our existing grain columns consisted of three columns: a beer column, extractive column (ED) and rectifying column (EDR), all operating under atmospheric conditions and each with their own steam supply for operation. In order to reduce the energy requirement of our columns, we worked with our designers/suppliers GEA Weigand to develop a design which allowed energy transfer between the columns. The greatest risk here was the potential impact on the final spirit quality. A lot of R&D was required to ascertain the following:

  • Impact of operating beer column under vacuum on the quality of the spirit;
  • IImpact of operating the rectifier under pressure on the quality of the spirit.

We commissioned a pilot plant, which was designed to 1/2000th of the intended grain columns. This allowed us to test and prove the proposed technology. Once we were happy with the outcomes of the R&D, we agreed on a design whereby the beer column operated under vacuum, the ED column under atmospheric and the EDR column under pressure. This allowed us to cascade the energy from the EDR column under pressure to the beer column under vacuum, which ultimately meant that this column was operated using waste heat recovery.

We also used MVR technology (mechanical vapour recompression) around the ED column to reduce its energy requirement. The resultant design has given us an energy reduction of 52% per lpa compared to our existing columns.

Low-temperature brewing and fermentation

Our continuous brewing system at Midleton has historically been high temperature brewing process where maize is milled, mixed with water, exposed to 150 degrees Celcius for four minutes to liquefy the starch. The mash is then flash cooled back down to 63 degrees Celcius, where malt is added and the malt enzymes convert the starch to fermentable sugars. The operation is effective but is energy intensive. As part of the expansion we designed a cooking process whereby we cooked our maize to 85 degrees Celcius, thus reducing the energy requirement.

This involved the installation of:

  • A new maize hammer mill. This replaced an existing cage mill in order to improve the fineness of the grist;
  • A new liquefaction vessel which replaced our cooker loop to allow the mash to rest for approximately two hours at 85 degrees Celcius;
  • A new convertor vessel to replace the existing one to increase residence time once again.

A fermenter is where the sugar-rich liquid from either the pot brewing or the low-temperature brewing processes is collected. Yeast is then added and converts this sugar-rich solution is to alcohol water and carbon dioxide. Each fermenter has external cooling coils to prevent the exothermic reaction from going out of control and killing the yeast. An increase in brewing and distilling capacity also required the installation of additional fermenters. Nine new fermenters were installed 4 on the pot side and 5 on the grain side.

Every distillery has to deal with both solid and liquid wastes from the process. There is spent grain from the pot brewing process and liquid wastes from pot distilling as well as solid/liquid wastes from the grain distilling. At Midleton, we have a feeds recovery operation which process these wastes and produces revenue generating by-products namely Distillers Dark Grains (DDG), Distillers Wet Grains (DWG) and Distillers Syrup (DS).

Before the expansion, the feeds recovery operated either producing DDG or DWG with an evaporator continuously producing DS. In order to eliminate the feeds recovery bottleneck, we upgraded the feeds recovery to enable dual production of DDG and DWG – effectively doubling the capacity of the feeds recovery operation.

Water for our process is sourced from the local Dungourney River. The water is extracted from the river and is passed through a process water-treatment plant with a filtration system. We have an existing underground cavern water source, which we can also use for fermenter cooling. Conscious of the additional water requirement caused by an increase in plant capacity, we also installed a number of boreholes throughout the site which will be used to supplement our water requirement.

This borehole water will have two uses: it will initially be used as cooling water for our fermenters to supplement the cavern water. This borehole water will then be returned to the process water treatment plant, put through a softener as the borehole water has a much higher level of hardness than the river and then mixed with the abstracted river water before being used as process water throughout the site.

Overall outcome of the expansion

Looking back at the original objectives of the expansion, we successfully achieved a doubling of the capacity of the distillery without altering the flavour, taste or quality of the pot distillates or grain distillates. We also by using modern technology succeeded in reducing the overall energy requirement per litre of pure alcohol by 20%. All in all, it is a very successful outcome from a very challenging but enjoyable time in the history of distilling in Midleton. O'RiordanChemDPS Engineering,innovation,Ireland,process engineering
  Authors: Brian Nation, master distiller, Irish Distillers Pernod Ricard and Maire O'Sullivan, senior process engineer, DPS Engineering Irish Distillers Pernod Ricard, in Midleton, is the home of Jameson Irish Whiskey and a number of other well-known brands such as Paddy, Midleton Powers and the single Pot Still range Red Breast,...