Understanding filtration › 5. Processes by sector

CHAPTER 5.1

Breweries

In the brewhouse, the filter cloth separates the sweet wort from the spent grains, brew after brew. It works in contact with a hot food product, between two cleanings, and its performance shows in the extract yield, the wort clarity and the brewhouse throughput.

Nicolas Ract · 7 min read · October 2026

Where separation sits in the process

General guidance: the crushed malt is mixed with hot water in the mash tun; enzymes convert the starch into sugars. The result is the mash, a slurry of sweet liquid and grain particles. The liquid, the wort, must then be separated from the solid part, the spent grains, before the wort is boiled with hops. This step is called wort separation, or lautering.

Separation takes place in two stages: the first wort is collected first, then sparge water is passed through the spent grains to extract the remaining sugar, until the desired volume is reached in the kettle [1].

Lauter tun or mash filter

The lauter tun is a vessel with a perforated false bottom. The barley husks settle on it and themselves form the filter bed: the quality of separation therefore depends on the grist, which must remain fairly coarse [1].

The mash filter is a plate filter press whose chambers are fitted with cloths. The mash is pumped into the chambers, the wort passes through the cloths and flows into drainage channels, then membranes inflated with compressed air squeeze the spent grains to drive out the remaining wort [2]. Since the grain no longer serves as the filter medium, the grist can be very fine (hammer mill), which improves extract yield, and the recipe can contain a high proportion of unmalted cereals [1]. At the end of the cycle, the filter opens and the almost dry spent grains drop out [1]. The principle is detailed in chapters 2.1 and 2.2.

Summary based on [1] and [2]. According to the same source, some brewers consider that the lauter tun produces better-quality wort [1]: the choice of equipment remains a trade-off for the site.

The yield gains claimed by equipment manufacturers are significant, in the order of 10 to 15 % more extract than a lauter tun according to a brewing trade press article written by a supplier [3]. These figures should be checked against the site's own recipes.

Other separations

A brewery has other separation steps: recovering the beer contained in surplus yeast and tank bottoms, and clarifying the beer before packaging. General guidance: these often use other technologies (centrifuges, sheet or precoat filters, membranes), whose media differ from filter press cloths. This chapter focuses on wort separation, where the cloth plays the leading role.

What wears or blinds the cloths

In a mash filter, the grid plates are covered on both sides with a monofilament polypropylene cloth [2]. This choice is no accident: monofilament promotes cake discharge and resists blinding (see chapter 3.2). The cloth's main enemies are:

• fines from the grist, all the more numerous the finer the grist;
• proteins and fats from the grain, which form a film in the fabric;
• poorly adjusted filling: underfilling lets sparge water pass through the empty part of the chambers, overfilling densifies the mash and hampers filtration [2];
• heat and cleaning agents, which must stay within the limits of the fibre (see chapter 3.1);
• Field experience: residues left by incomplete cleaning, which dry in the fabric between two series of brews and harden.

Cleaning in place

The filter is rinsed and then preheated with hot water before each brew [2]. Field experience: between series of brews, breweries carry out cleaning in place (CIP) with alkaline and acid solutions, at temperature, according to a programme validated by the quality department. For the cloth, three points matter:

• the compatibility of each product, and of its temperature, with the fibre;
• whether the solution actually reaches all of the fabric, including under the sealing edges;
• the final rinse, so as not to leave any product in contact with the next wort.

When filtration time no longer returns to its initial value after cleaning, the cloth is blinded in depth: the approach in chapter 4.4 applies.

What matters to the operator

• Throughput: wort separation governs the brewhouse sequence. According to the source cited, some brewers exceed twelve brews per day with a mash filter [1].
• Extract yield: sugar left in the spent grains is lost.
• Wort clarity: cloudy wort weighs on the rest of the process and on beer quality.
• Hygiene: the cloth is in contact with a food product; it must be fully cleanable.
• Spent grains: general guidance, they are most often used as animal feed; the drier they are, the easier they are to store and transport.

Indicators to track

The "Brewery" typical case in chapter 4.5 provides the framework. In practice:

• Service-life unit: the number of brews.
• Per brew: filtration time, wort clarity as measured by the site, volume and gravity of the wort collected.
• Per cleaning: date, programme, filtration time of the following brew.
• Per cloth: position, leaks observed at the plate edge (see chapter 4.3), reason for removal.

Field experience: a slow drift in filtration time over successive brews signals fouling; sudden cloudiness of the wort from a single chamber points rather to a punctured or poorly fitted cloth.

Choosing the medium: points to watch

• Food-contact compliance: ask for the food-contact suitability documents for the cloth and any finishes.
• Fibre and temperature: check resistance to the temperature of the mash, the sparge water and the cleaning, not just of the product (see chapter 3.1).
• Spent grain discharge: a smooth surface prevents spent grains from staying stuck when the filter opens.
• Retention: a finer grist requires a cloth that retains fines better, at the risk of blinding faster (see chapter 3.3).
• Edge and seam durability: leaks at the plate edge lose wort and dirty the filter (see chapter 3.4).
• Trial: any new reference is evaluated over a series of comparable brews, changing only one variable at a time (see chapter 6.2).