One's never enough. But we're not talking about my drinking habits, I was in Ireland for studying. So after the Midleton distillery visit, Tullamore (owned by William Grant and Sons) was next.
Though Tullamore is not the same scale as our last visit that there's a lot of money in whisk(e)y was once again apparent. The impressive looking distillery started production in 2014 and they've been busily filling up warehouses with casks since then.
Current production is 95,000 casks a year, an over production of 40,000 casks so an extra warehouse is built each year for storage. I told you there was a lot of money in whisk(e)y!
There were loads of fascinating facts to be had on this visit so I even got in touch with them afterwards to fill in some of the details. They don't just have continuous stills but continuous mashing too! Does it get more exciting than that? I don't think so! Still can't quite get my head round it all but here goes:
The continuous mashing can be thought of as like a tower of overflowing champagne glasses. Mash moves from the mill through a series of vessels where conversion takes place then on to the fermenter and then stills. They have two mashing streams which run alternately for approximately two weeks at a time.
They start with the hammer mill which mills 3,360kg/hr of wheat. No Steel's masher here, they have a plough mixer and and wheat slurry vessel. Steam is injected into a jet cooker giving a target temperature of 87°C. This will gelatinize the starch. As this is Irish Whiskey exogenous enzymes are used for starch breakdown. Alpha-amylase will help with liquefaction of the starch and break down long chain molecules in the starch exposing non-reducing ends which beta-amylase can act on to make fermentable maltose.
In a flash drum (a sealed pressure vessel run under a vacuum of 0.25barA) excess heat is flashed off bringing the temperature down to 67°C. The recovered heat is used to pre-heat the mash liquor. In a Conversion Vessel at 63°C beta-amylase and malted barley (2.5% of the grist) are added. Irish whiskey rules may allow the use of added enzymes but they still require at least some malted barley to be present.
The mashing process having higher then lower temperatures gets around the problem temperature stepped mashes commonly used in brewing have. By heating up the mash and getting to 63°C then going to 67°C you get the optimum temperature for beta-amylase action before the optimum temperature for alpha-amylase action so there are less of those non-reducing ends for the beta-amylase.
There's no grain separation so the mash/wash is cooled in a shell and tube heat exchanger on the way to fermentation. Having two of them allows CIP (Clean In Place) to be carried out on one whilst the other is in use. The total residence time of grain in the mashing system is around 50 minutes.
Fermentation takes 67-72 hours and then the wash and grains go to the
Continuous Stills. Those of you that have not had the benefits of a distilling education may not be aware how wondrous these are but I hope the pictures capture some of their majesty.
I can also highly recommend looking at a diagram of a
Coffey Still and following the flow round until you've worked out what on earth is going on. Then you'll truly appreciate continuous distillation! They get 99.5% efficiency compared to the Predicted Spirit Yield when making grain whiskey.
Going from right to left in the picture above is the wash column, purifier and rectifier. Further left there are another two smaller columns for the heads and tails which feed back into the purifier.
The wash column is run under 0.45barA of vacuum so raw alcohol is drawn at 72.6°C under normal running conditions. The top trays are a degassing section to remove CO2 and help prevent the carcinogen ethyl carbamate getting through to the final spirit. 130hl/hr of wash is run through the still. Spent grains carry forward from the distillation to a spent wash tank and are then separated out from the liquid "centrate" by a decanter centrifuge. The centrate, along with pot ale from the pot stills, is then evaporated making distillers syrup for animal feed and organic condensate which is used as process water.
The purifier has 40
trays and is packed with copper to remove unwanted sulphur compounds. The rectifier has 50 trays. Each of the trays can be thought of as a mini still so you can see why much purer spirits come from continuous stills than from pot stills.
Speaking of which, we saw them too:
The stills are in two sets of three, so wash, low wines and spirit stills. Products leave the stills at 26, 57 and 81.5% ABV respectively. The lyne arms, as you can see, slope down. I believe that's a lantern neck on the left still, though god knows what's going on with the off centre neck on the still on the right.
The mashing for the malt and pot (50/50 malt/barley) whiskey. The have one of those less efficient temperature stepped mashes for a 9.6 tonne grist (malt) or 8.5 tonnes (pot). Enzymes are added for the pot whiskey. The grist is wet milled and has a 20 seconds wet rest before milling.
Fermentation in the 12 fermenters (washbacks?) takes 72 hours, with a temperature ex-lauter tun of 22°C rising to 30-31°C during fermentation. Dried yeast is used and they do three brews a day.
Bourbon, refills and sherry casks are used for the malt and pot whiskey, bourbon and refills for the grain whiskey. The warehouse contain a mixture of cask types and ages so if one catches fire it won't leave a gap in the inventory!
My best guess from my scrawled notes for annual output in litres of pure alcohol is:
Pot whiskey 1.5 million
Malt whiskey 2.2 million
Grain whiskey 9.25 million.
I could have spent a lot longer here, I'd have loved to have seen the continuous mashing system. Chemical engineers don't always get things right but they do have their moments.
