Technological performance and features of non-
Bottle fermented and brewed beers are reaching more recognition in present days due to their high sensory complexity. These beers normally are produced by an initial tank fermentation to metabolize the sugars obtaining the typical alcoholic degree, and later the foam and CO2 pressure is produced by subsequent bottle fermentation. The sensory profile is improved by the formation of some fermentative volatiles, but also by the ageing on lees, because beers are brewed during several months with the yeast cells that performed the fermentation. The use of non-Saccharomyces yeast is a trending topic in many fermentative food industries (wines, beer, bread, etc.). They open new possibilities to modulate flavor and other sensory properties during fermentation and biological ageing. This chapter review the effect of some non-Saccharomyces yeasts such as Schizosaccharomyces pombe, Torulaspora delbrueckii, Lachancea thermotolerans, Saccharomycodes ludwigii, and Brettanomyces bruxellensis in the bottle fermentation and brewing of beers analyzing their metabolic specificities and sensory contribution on beer taste.
- non-Saccharomyces yeasts
- bottle fermentation
- Schizosaccharomyces pombe
- Torulaspora delbrueckii
- Lachancea thermotolerans
- Saccharomycodes ludwigii
- Brettanomyces bruxellensis
The beer-like beverages were already produced in the regions of Mesopotamia and Ancient Egypt since 5500 BC . Home-made or small-scale trade brewing supplied an essential part of diet to a primarily agrarian population. The historical development of brewing and the brewing industry is, however, linked with northern Europe where cold conditions inhibited the development of viticulture.
Although the main malted cereal for brewing is barley, other cereals such as oats, maize, rice, rye, sorghum, and wheat are malted for specific purposes, mainly for the production of peculiar beers. From the tenth century, adding of hops became usual from Germany across Europe to replace, or at least supplement, the variety of plants, herbs, and spices popular at that time. Not only the pleasing flavor and aroma of hop but perhaps, more importantly, their action in protecting the beer from being spoiled by the then unknown microbes, eventually led to their wide-scale adoption.
According with Anderson , in the medieval and early modern period the scale of brewing ranged from a few hectoliters annually in the average home to hundreds, or occasionally, thousands of hectoliters in the largest monasteries and country houses. Domestic brewing still accounted for well over half of the beer produced at the end of the seventeenth century. On the eighteenth and nineteenth centuries, the population of Europe’s cities growth was accompanied by an increase in beer consumption. The leading European beer-drinking countries of nineteenth century were the United Kingdom, Germany, and Belgium. Large-scale production began on the nineteenth century with improvements of technology and scientific research on microbiology. First, little meaningful scientific research in brewing was carried out by Louis Pasteur whose investigations on wine and beer fermentations in the 1860s and 1870s showed the importance of eliminating deleterious bacteria . Emil Christian Hansen became the first to isolate a pure yeast culture at Carlsberg in 1883.
The twentieth century saw the expansion in the beer industry. The industrial cooling allowed the introduction into the market of lager beers. Currently, there is a resurgence in craft or microbrewers , the market of craft beers in the United States grew 12.8% in 2015, and a significant strengthening of the sector has also been detected in several European countries, where growth from 2009 to 2014 outstripped 90–145% in Switzerland, the United Kingdom, France, Italy, and Slovenia; 333–400% in Slovakia, Czech Republic, Sweden, and Norway; and more than 1000% in Spain .
Brewing can be defined as the making of beer or related beverages by infusion, boiling, and fermentation. The various processes, inputs, and products of a brew house are shown in Figure 1. First part of the brewing process consist in converting the raw materials—water, malt, adjuncts, and hops—into a fermentable wort. Malt enzymes assist in the conversion of starch to fermentable sugars by mashing. For that reason, prior to the brewing process the malting process activates the natural enzyme systems of barley by controlled steeping, germination, and kilning. Mashing was simply the process of mixing warm water with ground malt, and cereal adjuncts if used, and after a period of standing, as much of the liquid as possible was recovered. The mash is then transferred to a mash filter (lauter tun) to produce bright wort and to collect the maximum amount of sugars (extract) from the residual solid materials (“spent” grain). Wort boiling satisfies a number of important objectives such as sterilization of the wort, extraction of the bittering compounds from hops, coagulation of excess proteins and tannins to form solid particles (hot trub) that can be removed later in the whirlpool, color and flavor formation, removal of undesirable volatiles such as dimethyl sulfide (DMS), by evaporation, and the concentration of the sugars by evaporation of water. Hot trub does need to be removed if the beer stability is not to suffer. The wort is then cooled from almost boiling point to fermentation temperature through a heat exchanger using water as the main cooling medium. The temperature for fermentation (Figure 2) is different for ale or lager fermentation (typically 8–14°C for lager and 15–20°C for ale). Yeast is pitched into the cooled wort in the fermentation vessel. Once the fermentation of the wort is completed, it is important to remove the bulk of the excess yeast before maturation, generally by removing the beer from the settled yeast. Then green beer must be conditioned to produce a stable, quality product suitable for filtration, and packaging. This process is called aging (lagering in lager beers). The objectives of beer aging are chill haze formation, clarification, carbonation (to a limited extent), and flavor maturation (again to a limited extent).
Fermentations performed in closed cylindro-conicals vessels may be of either ale or lager type. At the end of primary fermentation, the bulk of the yeast is collected by the application of rapid chilling and we have a green beer. Maturation of green beer is needed to obtain flavor adjustment (diacetyl, SO2, and DMS), yeast sedimentation, carbonation, and colloidal stability.
Typically, ale fermentations are fully attenuated and subjected to a short low-temperature conditioning in a separate tank to adjust carbonation, precipitate chill haze, and allow some loss of undesirable flavor volatiles trough gas purging. As lager beers ferment at much lower temperatures than ale yeasts (and therefore much slower), they also require an extended period of cellaring for maturation and development of the beer flavor. Conditioning is carried out at low temperature for no longer than a few days. As with chilled and filtered ales, this part of the process serves simply to adjust carbonation, develop chill haze protection, and clarify the beer. After conditioning the beers are filtered and packaged.
Other recovering old production methods for innovation are the production of cask- and bottle-conditioned beers. With bottle-conditioned beers a base beer is used. This base beer are as nearly as possible completely attenuated. This allows accurate control of addition of priming sugars. After bottling, beers are held in the brewery for a period from a few weeks to a few months depending on the temperature. Products of yeast metabolism are excreted into the beer providing distinctive flavor . It is possible to apply this technique by adding pure cultures of different non-
From ancient times the elaboration of beer was carried out by spontaneous fermentations with exposure to ambient to air of the cereal slurry to induce “contamination.” Bit-by-bit species of the genus
According to Ref. , the use of
In brewing most of the strains of
The occurrence of other species different to
Other application of non-
Although there are different options of innovation in the brewing process (using special malts or adjuncts, hop varieties, water quality, etc.), new and novel brewing yeasts strains can be discovered to enhance the aroma and flavor characteristics of beer and provide opportunities for developing new beers. The production of most aroma-active compounds is strictly dependent on the yeast strain chosen for the fermentation [13, 14]. This makes the selection of suitable strains the most important task to make good beer and opens new innovation opportunities to gain market especially in the market of craft-beer, to improve aroma profile after inoculation of non-
3. Use of non-
Saccharomycesin beer fermentation and ageing
The use of non-
The typical yeast species used in beer fermentation, and in most of food fermentations, is
Beer yeast can be classified in top and bottom-fermenting yeasts even when both belong to
The use of non-
The main fermentative properties of interesting non-
|Yeast species||Fermentative power (% v/v ethanol)||Able to ferment||Volatile acidity (g/L)||Volatile compounds||Effect on acidity||Ageing on lees||References|
|Neutral||Depending on strains|||
|Neutral||Moderate-high||[4, 23, 24]|
|Acidity enhancement lactic acid production||Depending on strains|||
|Maloalcoholic deacidification||Osmophilic high release of cell polysaccharydes||[16, 26, 27]|
|<0.5||Diacetyl, acetoin||Neutral||Osmophilic high release of cell polysaccharydes||[9, 28]|
|Acidity enhancement||Release of cell polysaccharydes||[4, 15, 19, 29–31]|
One of the most studied non-
It has also been described as a low producer of several volatile metabolites such as acetaldehyde, acetoin, and H2S that can be unpleasant at high concentration [17, 25, 32]. Sequential fermentations with
Enhance the production of 2-phenylethanol and glycerol during fermentation [25, 36],
Metabolism of organic acids is peculiar in
Some repercussions of
The influence in aromatic profile is because of the production of esters giving a fruity taste.
Also, it has being described as an osmophilic yeast with thick cell wall and is able to release higher amounts of polysaccharides from the external covering during autolysis. The release of polysaccharides is quite similar to
Traditionally, it is considered as spoilage yeast in enology because of the production of off-flavors, especially excessive amounts of acetoin and diacetyl. However, new applications are open currently in beer fermentation because of the lower amount of fermentable sugars.
The production of acetic acid by
In wines it has been described as producer of several off-flavors “Brett taint” [29, 52], most important are ethylpehnols.
Selection, isolation, and counting of non-
4. Sensory effects of the use of non-
Saccharomycesin beer conditioning and ageing
There are several hundreds of flavor-active compounds in beer. The main fermentation products of the brewing yeast are ethanol and carbon dioxide. Other molecules produced in smaller concentrations by yeasts during fermentation as metabolic intermediates or byproducts have great impact on beer flavor and determine the final quality of beer.
Several factors affect yeast fermentation with considerable influence on sensory profile of beer, some of the most relevant are pitching rate, temperature, duration, aeration, and C/N ratio [6, 15]. Also important is the specific species or yeast strain used . Some of the most important descriptors in sensory analysis of beers are described in Figure 4.
Secondary metabolites can be divided in several groups including fusel alcohols, esters sulfur-containing flavor compounds, undesirable carbonyl compounds, volatile phenols, organic acids, and monoterpene alcohols . Higher (fusel) alcohols and esters are the most important flavor-active substances in beer. Higher alcohols contribute to alcoholic taste, spicy, vinous, pungent aroma, and esters to fruity aroma of beer. Isoamyl acetate is considered a major contributor to the fruitiness of beer. However, it is possible that the presence of different esters below their threshold levels can exert a synergistic effect and play a role in beer flavor .
The synthesis of fusel alcohols in beer fermentation is linked to the assimilation of the nitrogen sources by yeast and, therefore, typically the consumption and production of amino acids. Esters are formed later via reactions of alcohols (ethanol and fusels) and acids (AcylCoA compounds). These reactions are catalyzed by specific enzymes called acyl-alcohol transferases or esterases. When some non-
Sulfur compounds are also produced by yeasts during fermentation, some of them behave as off-flavors and they have low sensory thresholds but others help to improve and modulate sensory profile of beers. Sulfur dioxide and hydrogen sulfide are included in these compounds , and they also have antioxidant properties and influence in flavor stability and increases shelf life. Hydrogen sulfide can be considered as a typical off-flavor in lager beers; however, at low concentrations it can be considered a typical aroma in some ale beers . Generally,
Among carbonyl compounds the presence of diacetyl above the threshold levels is responsible of a buttery odor generally undesirable in lager beer but can be an interesting attribute in some beer styles such as English pale ales . Diacetyl is reduced initially to acetoin and later to 2,3-butanediol, both with lower flavoring activity . Malolactic fermentation by lactic acid bacteria (LAB) is a strategy widely used in wine making to enhance the production of diacetyl. In beer brewing, LABs are sensitive to hop bitter acids . Increasing of temperature at the end of fermentation promotes the removal of diacetyl . The levels of acetoin and diacetyl can also be enhanced by using non-
The main volatile organic acids that occur in beer are acetic, propionic, isobutyric, butyric, isovaleric, valeric, caproic, caprylic, capric, and lauric acid. If they are present at high concentrations they contribute to sour and salty flavor to beer and can also contribute to off-flavors such as cheesy and sweaty .
Lastly, some terpenic compounds from hops and with positive repercussion on beer flavor can be released and enhanced by some enzymes expressed by yeasts .
5. Sensory aspects related with engineering and brewing process
Beer-making process with inputs, byproducts, and residues can be seen in Figure 5. Wort boiling is the most energy-consuming operation and different alternatives to reduce the consumption of thermal energy have been implemented. High-gravity brewing has been a common practice in many commercial breweries, especially in lager beers . Worts with a very high specific gravity (HSG; >16°P) are fermented to obtain a very high ethanol content beer. This beer is then diluted to reach the normal ethanol content.
According to Lodolo et al.  elevated osmotic pressure and the dilution of other essential nutritional factors such as amino acids contributes toward poor fermentation performance. The use of worts with high specific gravity (HSG) results in an unbalanced flavor profile [13, 14] and severe overproduction of acetate esters .
Another aspect related with brewing process is the use of large lager fermentation vessels in big-scale production. Fementor design can lead great pressures inside and excessive top pressure leads to poor yeast growth [13, 14]. The higher hydrostatic pressure in tall fermenters increases the concentration of carbon dioxide dissolved in beer and affects the stratification and irregular distribution of CO2 during fermentation. The excess in dissolved CO2 inhibits yeast growth and metabolism [13, 14]: poor diacetyl reduction and, most importantly, low ester production. However, according to Verstrepen et al. , in high gravity brewing (HGW) or when high fermentation temperatures are applied, the excessive formation of esters could be reduced by the use of tall fermenters.
On the other hand, some innovative brewer rooms are equipped by horizontal tanks that can be refrigerated by cooling jackets. Horizontal geometry leads to control yeast growth, modulates the ratio between higher alcohols and esters, and affects the flocculation, being possible to keep more suspended yeasts at the end of fermentation. Moreover, this geometry improves cleaning by CIP systems, and promotes the formation of aromatic esters.
6. Conclusions and future trends