THOUGHT PIECE the carling team
Brewing Is More Complex Than Wine Making….
We hinted last time that brewing beer or wash for making malt whisky was a lot more complicated than making wine or cider as the sugars for fermentation are not immediately available but are bound up as starch in the barleycorn.
Along with fermentation you can argue that mashing is the most important part of the brewing process regarding the effect it has on the character of the resulting beer. Compounds from the ground-up malt and adjuncts are solubilised into the wort involving the action of enzymes. These have been activated by the malting process and each has particular process optimum conditions of substrate concentration, pH, temperature, time etc which have to be balanced to yield the maximum amount of desirable wort components.
Put very simply, the endosperm of the barley corn comprises cell walls consisting of glucans encasing proteins and starch granules. To get at the starchy material and break it down into sugars to power the germination process, the cell walls and proteins first need to be at least partly degraded. Malting is a controlled germination which starts the degradation of structural glucans and proteins while activating amylases which will yield the fermentable sugars.
Then mashing the malt is a balance as well, Glucan levels in the wort should be low to prevent higher wort and beer viscosities leading to slower run off and filter rates. So here we have the first ‘additive’ as brewers wanting a faster brewhouse and filtration operation will add a litre per tonne of β-glucanase enzyme derived from the fungus Rhizopus microspores. This is needed as today’s barley varieties and malting regimes lead to lower levels of that enzyme in the malt and must be augmented if you want to accelerate the wort run off.
Then high molecular weight proteins produce desirable foam in the beer as well as unwanted haze. Limit dextrins where the amylase enzymes avoid the branch points in the starch molecule give mouth feel so complete degradation of the starch would produce a thinner and more alcoholic product. If malt particles are too large or the cell walls are largely intact, enzymes and indeed the water itself cannot reach the substrate so a more exhaustive step temperature mash regime will need to be employed to complete the malting process in the mash tun before converting the starch. Thus the process of mashing hides a complex mixture of biochemical, chemical and physical processes.
Years ago mashing was a hot and sweaty part of the brewhouse process. A gang of men armed with mashing paddles would cluster around the mash tun full of hot water. The brewer would adjust the temperature so that he could just see his face reflected in the water surface. We now know that is around 71oC. Sacks of milled malt nearby would be tipped in and frantic stirring would ensue. The first worts were run off through a perforated base of the vessel, more hot water was added and the whole lot was mixed up again. A third stir added the third water, then it was no doubt time to have a beer!
Earlier still mediaeval monks with smaller vessels would have pressed a ladle into the top of the mash to collect wort and transfer it to the copper for boiling with herbs rather than the now ubiquitous hop. Once the mash was too dry to get any more strong wort, more hot water would be added and the process started again.
Without a thermometer, some European brewers would mash at blood heat, then boil about one third of the mash and then recombine in a process called decoction. That needed a second vessel but consistent thermometer-free mashing was possible and a process called decoction with three mash boils was born and persists to this day. Continental malts tended to be less well modified than the maritime grown barley in England so the rise in temperature through the optimum for proteolysis and then starch breakdown was pure serendipity.
A triple decoction is part of the USP of Pilsner Urquell (now an Asahi brand) and is still employed at Plzen in the Czech Republic. The mash boiler is heated directly by gas with chains clanking over the bottom surface to prevent charring. The PU mashing process takes a full four hours from mash to lauter transfer and of course is rather energy intensive.
FIRST GRIND THE MALT AND THEN HYDRATE THE GRIST:
The cereal grist of malted barley with added coloured malts, perhaps wheat or other cereals first needs to be ground. Smaller brewers use two roller agricultural bruisers, then there can be two pairs of rollers and even three with or without intervening screens to get the correct spectrum of particle sizes for the method of wort separation being used. Mash tuns need a coarse grind with as much integral husk as possible to help filtration. Lauter tuns can be slightly finer. Mash filter grist can be pulverised. Why? We shall see in a bit.
The first stage in mashing is to hydrate the ground up grains with hot water. The water temperature must be calculated to get the desired finished mash temperature of around 65oC. Obviously in a smaller brewery on a Monday morning in the dead of winter, this temperature would have to be higher than mid-week in a modern well insulated brewhouse. The grist and water must be intimately mixed at around 2.0 – 2.5L per kg. This is accomplished with a hydrator where the grist is fed over a spreader to distribute it thinly while hot water is sprayed into the falling curtain of grist either using a vortex sweep or straight injection through a perforated tube.
The Steel’s mashing machine has been around for a century and a half and still delivers good service. The grist falls through a slide into a chamber into which the hot water is pumped. The mix is then carried forward using an auger into a second section where rotating paddles (from the same drive) ensure the grist is totally wet. The mash then plops with a satisfying sound straight into the mash vessel via a downward trumpet.
The traditional mash tun could have up to a 1.8m depth of grain although the old kieves (Irish mash tuns) at Guinness were 80” (over 2m). The tun has a false bottom and a graining arm sitting on the base which is raised by a hydraulic motor which then sweeps round and pushes the spent goods out through two plug holes.
Rotating sparge arms sit just above (and sometimes in) the top surface of the mash. Before mashing the base of the tun is flooded with hot water. After mashing there is a 45 – 60 minute rest while enzyme action completes. Hot water is then underlet below the plates to ensure the grain bed is not sitting tight on the bottom and run off can commence via a swinging inverted U tube or some other weir device to avoid sucking the bed down as far as the plates. The secret is to get the strong wort off slowly with the levels of the grains dropping steadily before sparge water is added to leach the rest of the sugary wort from the grains. Sparging can commence at 73oC and gradually increase to 76oC to reduce the viscosity and make run off faster. A total sparge of some 4.0 – 4.5L/kg will be put through the bed to recover the extract. 90-93% of laboratory extract should be achieved. Run off depends on bed depth and can take up to four hours. The grains are then removed and either sold for cattle feed or run to an anaerobic digestor where it is mixed with other brewery residues and the resulting methane powers the boilers for the next brew, Vessel residence time is quite lengthy but it is possible to turn smaller mash tuns around in eight hours and so carry out three brews a day.
SPLITTING THE UNIT OPERATIONS:
The solution to increasing throughput lies in splitting the unit operations of mash conversion and wort separation into two separate vessels. The first would be a mash vessel followed by a lauter tun or a mash filter. It is possible to turn a modern brewhouse around up to 16 times a day with a small wort cast out volume without too much loss of extract.
The modern mash vessel is a stainless steel stirred cylinder with a dished base and heating jackets. Mash flow from the hydrator would be directed down the side of the vessel to minimise oxygen pick up or else is pumped into the base which is certainly the case with steep conditioned mills which produce the mash as part of the milling process. Design of the impeller is vital to guarantee good mixing without any hot spots as the temperature is raising prior to transfer to separate the solid grain residues in the lauter tun or mash filter.
The term lauter comes from the German ‘abläutern’ which means to ‘rinse out or purify’ or in our case to clarify. The grain depth would up to be 18”, so for the same grist loading, the lauter tun would have to be wider than an equivalent mash tun. Guinness’ latest brewhouse in Dublin has a 14m diameter vessel on one of three brew streams, the other two are only 11.7m! Wort drainage is encouraged by raking the grain bed with knives which circulate through the bed to keep it open and wort flowing. A shallower grain depth will lead to faster run off and some wider versions have eight circulating arms supporting the knives. It is possible to turn the smaller ones around some 14 times a day but most brewers prefer a mash every two hours and get an increased volume from a slightly deeper bed twelve times a day with a yield of 97% of possible extract.
Faster throughput and easily sixteen brews a day are possible with a mash filter. Here the grain depth is only a few centimetres and the bed is supported against polypropylene cloths in a filter equivalent in size to a lauter tun well over 20 metres across. A flexible membrane can gently push the bed to expel the wort and as the pressure relaxes, sparging water can feed into the resulting gap which is then pushed through the bed to recover a seemingly impossible 102% of extract. The standard laboratory test for malt extract is based on a coarse grind, the mash filter uses a very fine hammer milled grist and the process leaves less extract behind. Hammer milling is quite energy intensive and requires exhaustive explosion protection. The gravities of recovered extract are higher, the wort is brighter, sparging is lower so there is no need to collect the last runnings to use in the next mash and the spent grains are also drier.
Why isn’t everyone using mash filters then? It comes down to cost. Up to twelve brews a day, the lauter is probably more cost effective with the filters coming into there own if you want to go faster. Turning a pair of 17 tonne filters around every 90 minutes would be only a far-fetched dream to our manual mashers we saw earlier.
Score so far, one ‘additive’; there will be more in fermentation and beer processing.