2.1. Grains and Malted Cereals
Cereals are the main ingredients for beer production; they provide nutritional sources for the fermentation progress, principally in the form of sugars. The main carbohydrate in the grain is starch, which is unfermentable and unusable by brewing yeasts. For this reason, prior to being used in the brewing process, cereals must be malted to promote the synthesis of the enzymes required for starch hydrolysis in fermentable sugars. After the germination, malts are dried and kilned. At this stage, different kilning procedures (time and temperature) allow obtaining different malt types, such as base malts (pale), speciality (caramel), and roasted (chocolate, coffee) 
. Moreover, a wide range of malts, covering a plethora of beer styles, is available on the market.
Barley (Hordeum vulgare
L.) and wheat (Triticum durum
Desf. and Triticum aestivum
L.) are the main cereals used in the malt industries. Among these, barley malt accounts for about 90% of worldwide beer production 
. Whereas wheat malt is used in proportion with barley for the production of wheat (or sometimes ‘weiss’ or ‘weizen’) beers, characterised by distinctive cloudiness and persistent foam due to the major protein content of wheat malt 
. Belgium and Northern Germany are historically known for the production of traditional beers brewed with raw (Belgian Witbier) and malted (German Weißbier) wheat, which are included in the list of classical beer styles, and are now produced and exported worldwide 
The use of autochthonous cultivars of cereals is one of the most explored strategies for the regionalisation of beer production. In this regard, cereals used in brewing vary among countries and as a function of the desired features of the final products (Table 1
). Moreover, some of these cereals could be useful in producing beer with particular added value (e.g., gluten-free beer 
), providing different nutritional and sensory properties 
, and reducing production costs 
. Nevertheless, integrating the malting stage is considered a ‘bottleneck’ in the regionalisation of the beer industry 
, and autochthonous cereals are often used raw and unmalted as partial substitutes for barley malt.
Table 1. Cultivars, origins, and impact of grains that were recently investigated for their brewing potential.
||Impact on Beer Quality
|Durum wheat (cv. Senatore Cappelli)
||High polyphenol content, balanced taste, low sweetness.
|Einkorn, emmer and spelt
||Higher antioxidant activity and polyphenol content, more fibre, lower gluten content, and low extract yields.
|Tritordeum (cv. Bulel)
||Addition of slight acidity and higher free amino nitrogen.
|Triticale (cv. Remiko)
||Higher acidity, lower esters and isoamyl alcohol content.
|Rice (cv. Loto)
||Acceptable alcoholic content (3.5–4.5% vol.), good foam stability, rather poor in body and mouthfeel.
|Rice (cv. Centauro)
||Pale colour, not persistent foam, flat sensory characteristics. Optimisation of malt production improves colour and flavour.
|Oat (cv. Koneser)
||Increased protein content in the wort and prolonged filtration time.
|Oat (cv. Raisio)
||High pH and low alcohol content, strong berry flavour and low amount of staling compounds during ageing.
|Corn (cv. Nzaka-nzaka)
||Poor foam stability, saccharification needs of exogenous α-amylase.
|Pigmented Corn (cv. Chalqueño)
||Low-alcohol beer with polyphenols and anthocyanins with antioxidant properties.
||Slight alcoholic (3.6%), brown colour, and acid pH (4.15 on average) due to the alcoholic and lactic co-fermentation. Incomplete saccharification, residue of insoluble materials, increased viscosity.
|Red Sorghum (cv. DKS-74)
||Exogenous enzymes treatment yields glucose and alcohol content similar to barley-malt beer.
||Higher foam stability, lower level of soluble nitrogen, and more than twice the amount of fat; positive effect on the overall sensorial quality.
|Rye (cv. Dukato)
||Increased beer viscosity, higher palate-fullness.
|Teff (cv. Witkop)
||Higher content of glucose and a lower content of maltose, higher sweetness, fruity aroma, with little body.
The Mediterranean area is characterised by the presence of several cereal cultivars, in some cases only locally diffused, which could be exploited to improve segmentation in brewing regionalisation. Ancient wheat varieties have recently gained popularity due to their nutraceutical properties, from their higher concentrations of flavonoids, fibre, and minerals 
. In Sardinia, Italy, a craft beer brewed with the old Italian wheat cultivar ‘Senatore Cappelli‘ as an unmalted supplement (40%) was compared with two industrial wheat beers, resulting in higher polyphenol content and more balanced taste 
. Other Triticum
spp., such as einkorn (Triticum monococcum
L.), emmer (Triticum dicoccum
L.) and spelt (Triticum spelta
L.), are used to obtain malts with higher antioxidant activities and total polyphenol content 
, characterised by the presence of more fibre, lower gluten content 
, and low extract yields 
. New hybrids were recently assessed for malt and beer production. Among those, Tritordeum (x Tritordeum martinii
), obtained by crossing wild barley with wheat, was comparable to barley in saccharification time, lautering, as well as colour and turbidity, but a slightly acidifying effect and higher free amino nitrogen were observed 
. Whereas, Triticale (x Triticosecale
), a hybrid of durum wheat and rye, is suitable for malt production because of its high extraction capacity, high diastatic power, and short saccharification time, but with higher acidity and lower esters and isoamyl alcohol content 
Oat (Avena sativa
L.) is considered a functional cereal due to its pronounced level of antioxidants, fibre, and β-glucan. Compared to barley, oat is characterised by a higher husk content, which improves lautering performance, but leads to lower extract content, malted or unmalted 
. Beer produced entirely from oat malts also has higher pH, lower alcohol content, and an intense berry flavour 
, while any significant difference can be found in the protein profile and in the fermentation trend 
. The enhancement of extract and alcohol content by using exogenous enzymes, such as β-glucanases, amylases, neutral proteases, and hemicellulases, was reported on in the literature 
Rice (Oryza sativa
L.), due to its high starch content, is sometimes used in brewing as a supplement to increase the sugar content of the mash 
. Different trials were carried out in the production of rice beers 
. Nevertheless, its protein and enzymatic profiles are lower than barley, and, furthermore, its starch does not entirely break up during the malting and mashing stage 
. Despite the flat sensory profile and soft pale colour being reported in the first trials 
, optimisation of rice malt production resulted in an enhancement of flavour, taste, colour, and body of all rice beers, with encouraging results recently obtained 
Other grains, such as corn and sorghum, although they are considered as supplements for beer production, are commonly used to ferment traditional beers in South America and Africa, respectively, where they are the most cultivated cereals. Corn (Zea mays
) is used to produce several indigenous South- and Mesoamerican beers, commonly known as Chicha 
. Among these, Chicha de Guiñapo
, traditional of Arequipa (Peru), is based on malted-pigmented corn 
. Recently, pigmented corn malt was proposed as the main ingredient in different beer-style productions 
. Whereas sorghum-based African beers are characterised by a slight alcohol content (3.6% ethanol), brown colour, and acid pH (4.15 on average) due to the alcoholic and lactic co-fermentation 
. However, some problems, such as incomplete saccharification, residue of insoluble materials, increased viscosity, and low free amino nitrogen content, occur in brewing with sorghum malt 
. For these reasons, it is necessary to develop an appropriate process to improve malting and mashing conditions and the final sensory aspects. In this regard, the use of different formulations of exogenous enzymes has been evaluated. For example, β-amylase increases the amount of fermentable sugars 
, whereas amyloglucosidase treatment improves wort yield, resulting in higher alcohol content 
. Alternatively, the α-amylase, β-amylase, and amyloglucosidase activities of sorghum malts could be enhanced by the addition of koji (Aspergillus oryzae
Hops are the unfertilised female inflorescence of the perennial climbing vine Humulus lupulus
L., belonging to the family Cannabaceae. The importance of hop is related to its bitterness, which contributes to the characteristic aroma and flavour of beer. Hops also enhance foam formation and stability and have antibacterial properties protecting against spoilage by certain microorganisms 
. Their key compounds for brewing are resins and essential oils. Among the resin fraction, iso-α-acids, which originate when hops are added during wort boiling, are the most significant bittering compounds. Essential oils, mainly terpenoids, are extracted during late- and dry-hopping and are responsible for the beer aroma 
. The perceived sensorial attributes depend on the hop varieties 
and different commercial preparations (whole leaf, pellets, extracts) 
. Brewers formerly divide hops into two groups based on their bittering or aroma contributions 
. Among the most known cultivars, Target, Admiral, Nugget, Pride of Ringwood,
and Super Pride
release a high quantity of bittering compounds, while Fuggles, Goldings, Saaz, Willamette, Cascade,
varieties provide a pleasant hoppy aroma 
. Hop cultivars have a strong connection with the geographical contest. In fact, they are also divided into groups, such as American, German, British, European, and others, according to their origin. For example, aroma hop varieties, such as Hallertau
are denominated according to a German region and city, respectively, and are among the most cultivated hops in Germany. Saaz
is termed with the German name Žatec (Saaz), a city in the Czech Republic, and it is a traditional ingredient of Pilsner beer. Nevertheless, the United States and Germany are the most important producers, with about 50,000 tons for each, and Germany as the larger exporter, with 25,000 tons exported worldwide 
. In this regard, there is growing interest in the definition of hop terroir
and in presenting the differences among cultivars grown in different geographical contests. Table 2
shows the difference in terms of quality among hops from different terroir
. The dual-purpose American hop Amarillo
grown in Idaho has lower citrusy and floral notes but a more fruity, spicy, and resinous odour than Washington 
. In the same regions, the effect of terroir
was later confirmed for hexyl glucoside content, a green leaf volatile with a grassy aroma, in twenty-three hop cultivars 
. Similarly, Cascade
from the Hallertau has more polyphenols and esters, but lower terpene content than those grown in Yakima (Washington, DC, USA) 
. On the contrary, the same variety cultivated in Sardinia (Italy) had essential oils and acid content comparable to those farmed in the US 
. In this way, recent research compared the volatile fingerprint and the acid profile of 15 commercial international hop cultivars, grown in an experimental field of Central Italy, with their standard characteristics, discovering desirable acids and terpene content in the cultivars Chinook
and Hallertau 
Table 2. Cultivars, origins, and impact of hops recently investigated for their brewing potential.
||Impact on Beer Quality
||Low content of alpha acids, citrus-like aroma due to geranyl esters content of essential oil fraction.
||Terpenoid profile similar to the parental variety Strisselspalt, gives spicy and herbal notes to the beer.
||High concentration of monoterpenoids, especially linalool, which bring a floral note to beer.
||Lower citrusy and floral notes, but higher fruity, spicy, and resinous odour descriptions.
||Higher content of polyphenols and esters, such as isobutyl-isobutyrate and 2-methylbutyl-2-methylpropanoate.
||Higher linalool contents with respect to those grown in Hallertau (DE).
||Essential oil and the α-/β-acids in the same range of those cultivated in the US.
||Higher content of farnesene and selinene, but lower levels of humulene and myrcene respect to the US grown crops.
||It contains a unique volatile compound, geranic acid, which enhances the aroma contribution of terpenoids at sub-threshold levels.
||Selinenes, α-acids, trans-β-farnesene, and α-caryophyllene/β-humulene ratio are the main contributors and have a higher content of xanthohumol and α-acids among European wild hops.
||High content of myrcene and low contents of humulene, farnesene, and selinenes.
||Significantly lower cohumulone content.
The breeding of new varieties is another way to expand the plethora of hop cultivars, and to select those suitable for specific regions. In France, the variety Strisselspalt
was used as a parental strain to obtain the new ones, Bouclier
, which showed significantly different terpenoid profiles 
. While the variety Kazbek
was bred in Czech Republic as the first aroma hops variety with a specific citrus-like aroma for Pilsner beer 
. Sorachi Ace
, the most known Japanese hop, has a significant amount of geranic acid, enhancing the varietal aroma of the hop-derived terpenoids 
Evaluating the brewing potential of wild hop varieties is one of the new tools used in the regionalisation of beer production. Mongelli et al. 
characterised the aromatic profiles of 22 Italian wild hop genotypes. The low essential oils and bitter acidic content of some of these ecotypes suggest a potential exploitation, for a dual-purpose or for dry hopping hops. In addition, a comparison between wild hops collected from different regions of North America and the Caucasus showed significant differences in the contents of α- and β-acids, cohumulone, and colupulone amount 
Among microbes, yeast plays the most important role in beer production, as it ferments the wort, metabolises the sugar, and produces the compounds that define the peculiar characteristics of the beverage. It is also crucial for defining the flavour and aroma of the final products, including the synthesis of higher alcohols, esters, aldehydes, and organic acids 
, but also the bioconversion of hop-derived compounds 
. For this reason, yeast starter cultures, in some cases, are protected and included in the list of autochthonous and/or traditional ingredients of regional beers (e.g., Münchener Bier) 
. In brewing, yeasts are formerly divided into two major groups, based on beer-style, working temperatures, and flocculation ability. In the first group, there are those belonging to the species Saccharomyces cerevisiae
, which are suitable for ale beers, capable of fermenting at warmer temperatures (16–22 °C) and able to flocculate or aggregate at the top of the vessel once fermentation is complete. In the second group, there are natural hybrids between S. cerevisiae
and S. bayanus
species, known as S. pastorianus
(syn. S. carlsbergensis
), suitable for lager-style; they ferment at lower temperatures (6–16 °C) and settle to the bottom of the vessel at the end of fermentation 
. The two styles also need different periods of maturation: lager beers undergo a long, low-temperature period of ageing (known as lagering), while ale beers are usually mature in a short period 
. The world beer production is represented by 90% for lager, and 5% for ale, while the other 5% is produced by spontaneous fermentation 
. The latter has a particularly sour taste resulting from the sequential or contemporary fermentation by different microbes, among which, Saccharomyces
and lactic acid bacteria (LAB), such as Lactobacillus
, are considered the most important for the final beer character 
. In the traditional Belgian lambic style, and its analogous American coolship ale, the wort is exposed to air during cooling and then transferred to wood barrels used in previous fermentations, resulting in a spontaneous inoculation by a consortium of microorganisms 
. A microbial population of more than 2000 strains has been documented in lambic fermentation 
. Nevertheless, the complete maturation of these kinds of beers can take many years, making it difficult to obtain a suitable quantity of products for commercial purposes 
The demand for novel starter cultures for brewing is increasing, and brewers and scientists are converging on the selection of those that could bring added value to the final products. Nowadays, the definition of microbial terroir
has assumed relevant significance in wine production 
; however, this approach has only recently gained popularity among breweries. In brewing, microbial terroir
could be associated with the use of native microbes, isolated from traditional beer ingredients, but also with those strains isolated from other autochthonous biological resources. In fact, different research trends are focusing on improving the microbial biodiversity useful for beer production, including the exploration of the brewing potential of different groups of microorganisms, such as Saccharomyces
strains isolated from other fermented food and beverage hybrids of the Saccharomyces
genus and non-Saccharomyces
. Thus, the features of relevant interest comprise sugar utilisation (mainly maltose and maltotriose), hops and ethanol tolerance, and ethanol and flavouring compound production (e.g., esters and higher alcohols) 
. Table 3
reassumes the main microbial strains recently investigated for their impact on beer quality.
Table 3. Species, strains, origin, and impact of microbes recently investigated for their brewing potential.
||Impact on the Beer Quality
||Higher fruity and flowery aroma compounds in bottle re-fermentation.
|S. cerevisiae S-42
||Similar sensorial profile, higher acidity, higher ethanol and esters content.
|S. bayanus × S. cerevisiae
||De novo hybridisation
||Efficient consumption of maltotriose, appreciable level of aroma compounds.
||Hanseniaspora guilliermondii IST315
||Increasing eight times the content of phenylethyl acetate, associated with rose and honey aroma.
|Hanseniaspora vineae T02/05
||High ester production, fruity aroma suitable for low-alcohol beer production.
||Rye malt Sourdough
||Clean flavour profile and tolerance to low-temperature conditions.
|Lachancea fermentati KBI 12.1
||Lactic acid production, lower alcohol level, fruity aroma.
|Lachancea thermotolerans MN477031
||Low lactic acid production with a minor impact on pH of the beer.
|Mrakia gelida DBVPG 5952
||Glacial melting water
||Low alcohol production and low diacetyl, and appreciable organoleptic characteristics.
||Production of the spice/clove aroma 4-vinylguaiacol, suitable for low-alcohol wheat beers.
|Saccharomycodes ludwigii DBVPG 3010
||Production of low-alcohol beer, higher content of esters, and lower amount of diacetyl.
|Torulaspora delbrueckii DiSVA 254
||Increase of aromatic compounds, emphasised fruity/citric and fruity/esters notes.
|Lactic Acid Bacteria
||L. brevis BSO 464
||High flavour intensity, acidic taste, and astringency in co-fermentation.
|Lactobacillus amylovorus FST2.11
||High sensitive to hops, acidification of unhopped wort until 5–6 g/L of lactic acid.
|Pediococcus acidilactici K10
||Starter for malt acidification; provides bioprotection against spoilage bacteria.
|P. acidilactici HW01
||In malt acidification, improves microbiological stability, viscosity, and filtration time.
species are responsible for the primary fermentation of a large variety of fermented food and beverages. However, the ability to metabolise maltose and maltotriose is not widespread, thus restricting the brewing potential only to a few species 
. Rossi and co-workers 
compared the fermentative ability in laboratory-scale fermentation and volatile profiles of different S. cerevisiae
strains isolated from grape must, bakery, and wine and apple stillage. The authors selected a baking yeast as the most promising strain, leading to features in line with ale profiles and with a pronounced contribution in esters (above threshold). In this contest, sourdough could represent an important source of biodiversity when selecting autochthonous strains suitable for craft beer production. This idea is supported by the fact that some regional beers, such as Finnish Sahti beers, recognised in the European Union as ‘Traditional Speciality Guaranteed’, are traditionally fermented using baking yeast strains 
. In this light, Ripari et al. 
reported for the first time the utilisation of the whole microbiota of artisanal sourdough, comprised of yeasts and LAB, to obtain sour beers inspired by lambic fermentation. Other studies confirmed the potential of sourdough yeasts. For example, in Sardinia (Italy), two S. cerevisiae
strains from artisanal sourdoughs were selected to produce wheat beers from the Italian cultivars ‘Senatore Cappelli’ 
. Among those, S. cerevisiae
S-38 has shown physical–chemical, volatile, and sensory characteristics comparable to the commercial strain Safale S-33 (Fermentis, Lesaffre, Marcq-en-Baroeul, France) 
, whereas S. cerevisiae
S-42 had higher ethanol content, lower pH, and a higher content of esters 
. While Catallo et al. 
used a sourdough strain as a parental strain in a de novo hybridisation to obtain a hybrid for lager beer fermentation. The authors reported that the hybrid inherited the ability to produce positive aroma compounds, such as 3-methylbutylacetate, ethyl acetate, and ethyl hexanoate by the sourdough strain, together with the efficient utilisation of maltotriose from the other parental strain 
yeasts have limited fermentation performance and are less tolerant to ethanol, but they produce volatile compounds, contributing to the sensory characteristics of several fermented beverages 
. For this reason, different genera have recently been investigated for their contributions to brewing 
. Among these, Dekkera
strains are the most known as they are considered the main spoilers in beer and wine production, but if applied correctly, they contribute to the production of exotic flavours and the aroma complexity of speciality beers 
. The enhancement of aromatic flavour in beer by different Torulaspora delbrueckii
strains of oenological origins, to the production of isoamyl acetate, has been well documented, in both pure and mixed fermentations with commercial starters 
. Meanwhile, the strains unable to ferment maltose Saccharomycodes ludwigii
and Zygosaccharomyces rouxii
have been studied to produce special beer styles, such as low-alcohol and alcohol-free beer 
. Differently, the use of species able in producing lactic acid, such as Lachancea thermotolerans 
, L. fermentati
, Hanseniaspora vineae
, Schizosaccharomyces japonicus
, and Wickerhamomyces anomalus 
has been investigated for the production of sour beers in a single step of fermentation. Different methods for producing sour beers, such as kettle souring, sequenced, and mixed controlled fermentation, were recently explored 
. Sour beers, such as the German Berliner Weisse and Gose, and the spontaneously fermented Belgian lambic and American Coolship Ale, have an intentional acidic taste given by the fermentation of acid-producing bacteria, mainly LAB, aside from brewing yeasts 
. In addition, since LAB could be isolated from several food matrices, including brewing ingredients 
, they could contribute essentially to the regionalisation. In this regard, L. amylovorus
FST2.11, isolated from the brewing environment, was tested with different acidification methods, suggesting kettle souring as the best practice to obtain sour beer with minimal organoleptic failures 
. Contrarily, Dysvik et al. 
showed that beer co-fermented with LAB strains, such as L. plantarum
and L. brevis
BSO464, had an increased intensity in fruity odour and higher total flavour intensity, respectively. These suggest that organoleptic attributes could be species- and/or strain-dependent, rather than method-dependent, since pre-acidification of the wort did not surpass that obtained by chemical acidification 
The use of unusual ingredients is widespread among breweries, and although they are not essential for beer production—they are often used for the production of speciality beers. However, concerning the high number of commercially available products belonging to this category, only a few data are available in the literature. Among adjuncts, fruits and spices are often used to enrich the flavour complexity of certain beer styles. For example, orange peel and coriander are traditional ingredients of Belgian Witbier 
. Fruits (as whole or as juices) are among the most studied supplements, and they are already present in many commercial products 
. In Belgian lambic-style, for example, whole raspberries (Rubus idaeus
L.) and tart cherries (Prunus cerasus
L.) are traditionally used in the maturation of Framboise and Kriek beers, respectively 
. Recently, the Beer Judge Certification Program recognised the Italian Grape Ale (IGA) as the first Italian style, which could be an expression of the regional biodiversity, promoted by the wide availability of grape cultivars 
. In IGA, grapes can be added up to 40% during mashing, fermentation, and maturation. In addition, the use of several fruits, such as bananas or persimmon, has been reported in the literature. In both forms, fruit supplementation increases fermentable sugars 
, adds flavour and fruity aroma 
, modifies the colour due to the solubilisation of pigments, such as carotenoids 
and anthocyanins 
, enhances antioxidant activity and total phenolics 
, increases bioactive compounds 
, adds a different degree of acidity 
, and increases alcohol content 
. In addition, these supplementary ingredients could represent relevant links to specific regions (Table 4
Table 4. Cultivars, origins, and impact of adjuncts recently investigated for their brewing potential.
||Impact on Beer Quality
||Banana (cv. Prata)
||Increasing of fermentable sugars and ethanol production.
|Persimmon (cv. Rojo Brillante)
||Addition of malic and citric acid, light orange colour by solubilisation of carotenoids, increase of fermentable sugars.
|Hawthorn fruit (cv. Aurea)
||Increase of antioxidant activity, polyphenols, and volatile aroma compounds.
|Cornelian cherry (cv. Podolski)
||Increase of polyphenols and antioxidant activity, addition of anthocyanins and sour taste.
||Slightly higher alcohol content, higher colour index.
|Cocoa (VP 1151)
||Increasing of wort viscosity, higher mineral, glucose and fructose content, higher ethanol production.
||Lesser variation in beer standard parameters, good acceptance in sensorial attribute.
||Carqueja (Baccharis trimera)
||Addition of bittering compounds, total substitution of hop has shown no negative effects, sensorial acceptance similar to commercial beers.
||Bittering effect, suitable for total hop substitution, good sensorial acceptance.
|Purple sweet potato (ST-13)
||High content of anthocyanins and antioxidant compounds, peculiar pink colour.
||Promoting secondary fermentation by LAB in sour beer.
||Increase polyphenol content but not antioxidant activity, sour/astringent taste and herbal aroma at 10 g/L, pleasant sensory profile at 5 g/L.
|Eggplant (cv. Classic) peel extract
||Increase of antioxidant activity, phenolics, and flavonoids content, reddish colour due to the release of anthocyanins.
Other ingredients can also be added to contribute to bitterness. In fact, before hops introduction, beers were initially flavoured with a mix of herbs and spices called gruit, which contained several herbs and spices 
. Therefore, other bittering plants were investigated as hops substitutes, including where hop cultivation was not suitable. For instance, artichoke and carqueja were positively evaluated in Brazil as total substitutes because of their good sensorial acceptance and the absence of negative effects on physicochemical characteristics 
The regionality of the adjuncts is only poorly evaluated; however, intriguingly, attention is placed on the use of by-products from the food industry 
, with the incremental aim of reducing food waste and its economic weight.