A holding hopper (often called a scale hopper or grist case) is used for grist and is mounted above the cereal cooker or the mash tun (Figure 8.5). Hoppers are usually equipped with vibrators to aid in the emptying process. They have automatic load cells for exact weight measurement (to an accuracy of +/-1%). A dust collection system or a breather filter is installed on the holding hopper in order to minimize the dust.
Premasher is used to mix the brewing water and grist in order to break up the clumps of grist before moving to the mash conversion vessel (i.e., mash mixer or mash tun) (Figure 8.3). The three main types of premashers are: foremasher, Steele masher, mashing ring, or grist hydrator. A foremasher is nothing more than a tube where the malt flows down and inside this tube there is a smaller tube where the water flows out and mixes with the grist. Another option is a Steele masher which uses an auger and blades to mix the grist and brewing water together. Steele mashers are preferable when milling/mashing rates are greater than 50 pounds per minute. For slower mashing rates, a simple mashing ring can be used.
British brewers use the same vessel—commonly referred to as the “mash tun”—for both mashing and wort separation. Mash tuns can only be used for infusion mashing (single temperature) and as a result under-modified malts or malts requiring a protein or glucanase stand cannot be used. A mash tun has the form of a round insulated enclosed vessel of approximately 10 meters in diameter and 2 meters in depth, although this will vary according to the size of the brewery. The mash tun is fitted with a false bottom with slots of 1 mm width sitting just above the floor of the vessel.
Mash tun/lauter tun combinations combine all the functionality of a mash tun and a lauter tun, both key components in a brewhouse, into a single tank component where all brewing processes take place—mashing and wort separation. The mash/lauter tun is the preferred by many craft brewers (Figure 8.7). The mash/lauter tun is the most cost-effective system in terms of capital investment and the easiest to operate. Mash/lauter tuns are made of stainless steel and are equipped with a sparge arm for spraying high-temperature water (sparging) over the mash bed to displace the extract at the end of the mashing cycle.
Mash Conversion Vessel
Mash conversion vessels (i.e., mash mixers) are used to solubilize substances, through enzymic action, that are not soluble in their natural state, to dissolve substances that are immediately soluble, and to facilitate chemical changes through enzymic action (Figure 8.8). Mash conversion vessels are usually stainless-steel vertical cylinders equipped with a conical or dished bottom and with a large diameter agitator. It does not have a false bottom, which is different from that of a mash tun.
A mash kettle or mash cooker is used for boiling part of the mash for decoction mashing. Mash kettles are similar in construction to mash mixers, except that they often have agitators that are more powerful and more steam heated areas, since their contents must be heated to boiling.
Sometimes, if the kettle is not immediately available, the wort is held in an intermediate vessel, or underback, before it is boiled. It is held hot (75–80°C, 167–176°F) to minimize the risk of microbial infection. This “hold” should not be prolonged as some thermophilic organisms, including some that can reduce nitrate ions to nitrite ions, can continue to grow and the wort will darken and its flavor will alter.
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