Author Archives: Diogo Portugal-Nunes

Author: Diogo Portugal-Nunes

Expert in microbial fermentation and biotechnology. PhD in Applied Microbiology from Lund University, Sweden, where he investigated the application of specific bacterial and yeast species in the industrial biotechnology sector. He is currently a Product Developer at Harboe Brewery, Denmark, where he works on the development of innovative beverages, with a great focus on beer, and functional malt-based ingredients .

Kombuchawhaaat? If you have never heard about this beverage, do not be afraid! The pronunciation is easier than it looks and it is tastier than it sounds! Kombucha is a beverage that results from the fermentation of black or green tea leaves and cane sugar with several bacterial and yeast species – a Symbiotic Culture Of Bacteria and Yeast (SCOBY). Kombucha is one of the rising stars in the revival of specialty fermented beverages that has been taking place in the market over the last recent years.

The rise of fermented beverages, both in variety and production volume, has been defined as one of the most important trends in 2019 within the food beverage sector. To give you a more objective picture, the global fermented beverages market is expected to increase steadily until 2023, reaching 935 billion euros (in 2015 it was valued at 600 billion euros). The beverage consumers and the millennials generation in particular have a high interest on experiencing novel and unusual flavors together with different textures and the fermentation process can strongly influence those characteristics.

What makes kombucha unique

But why is Kombucha so special within the large variety of fermented beverages? Kombucha is a low-sugar tea-based fermented beverage with considerable levels of organic acids, vitamins and polyphenols, known for their health benefits. By adding fruit, herbs or flavors into this mixture you get a quite unique and refreshing beverage that is, most often, sparkling and non-/low-alcoholic. Kombucha can have a drier and/or tarter character like the traditional ciders or the “Brett” beers and the production of alcohol can also be boosted by adjusting the fermentation conditions (if alcohol is higher than 4.5% it is referred as Hard Kombucha). The explosion of flavors present in Kombucha can be quite overwhelming in the start due to its high acidity but quite addictive afterwards. The definition of Kombucha is quite broad and there is a great variety of flavors and profiles in the market at the moment, going from soft-drink like beverages with low sugar and high drinkability to more dry and acidic beverages that can be in the direction of sour beers or dry cider.

Tea and sugar are two central ingredients for the production of kombucha

One of the best parts about Kombucha is that you can produce it at home with a very limited amount of kitchen gear, no fancy equipment being needed.

There are several dedicated websites with infographics and videos that can be very helpful before you do your first Kombucha brew, where more detailed explanations about the gear required as well as recipes and how to find and get the SCOBY. In a simplistic way, the production process of kombucha requires two fermentation steps:

  • Primary fermentation:the mixture of yeast and bacterial species converts the sugar into ethanol and organic acids. At the start of the process, oxygen is present (aerobic conditions), which promotes the cell division of the yeast species and later conversion of sugar into ethanol and carbon dioxide (CO2). The type and proportion of yeast species varies from SCOBY to SCOBY but SaccharomycesBrettanomyces, Pichia and Hanseniaspora are some of the most common ones. When sugar is depleted, ethanol becomes the most abundant carbon source, which promotes the activity of the different bacterial species that will convert it into organic acids. Species belonging to the genus AcetobacterGluconobacter and Lactobacillus are the major responsible for the production of acetic acid, gluconic acid and glucuronic acid. Acetic acid, that gives vinegar aroma and taste, is normally the most abundant organic acid when the primary fermentation is finished. At the beginning of the process the SCOBY will be at the top of the flask and during the fermentation it starts to sink, forming a new SCOBY at the top. Thus, at the end of the primary fermentation you will have two SCOBYs that can be used for two new batches of Kombucha.
SCOBY – The Symbiotic Culture Of Bacteria and Yeast that is responsible for the formation of unique flavors and aromas in Kombucha (Image from BUCHI, www.buchi.com.au/)
  • Secondary fermentation: the Kombucha from the primary fermentation is filtered to remove the major particles and then flavored by adding fruit, juices, herbs, spices and/or others. The sugar addition from the flavoring step will promote the anaerobic fermentation of yeast, resulting in the formation of carbon dioxide (CO2) which naturally carbonates the final beverage. When this step is made directly in the bottle – bottle fermentation – it can be tricky since you need to calculate how much CO2 will be produced from the sugar added during flavoring. The first time you may get an over-carbonated beverage with too much fizz.

Even though there are many reports regarding the positive impact of Kombucha on the digestive system and gut health together with its action as anticarcinogenic, antihypertensive, antidiabetic, and hepatoprotective, it is important to note that currently, Kombucha cannot be granted with any official health claims. I believe that in a near future some concrete results from clinical studies will give a more accurate information regarding the active functionalities of Kombucha.

Kombucha flavoring step (image from ifoodreal, https:// ifoodreal.com/)

The Kombucha presence in the European market is still limited when comparing with the United States, where this fermented beverage can be found throughout the whole country. The implementation of Kombucha in Europe requires some more consumer education since it is a beverage with a unique and acquired taste, but it is clear that more and more people are becoming aware of its existence and benefits. Next time you see some Kombucha in a shop or pub, go for it and give it a try! Soon after there is a high chance that you will be planning your first brew of Kombucha at home.

Sources

https://www.globenewswire.com/news-release/2017/04/17/961353/0/en/Global-Fermented-Beverages-Market-2014-2016-2023-Launches-of-New-Products-are-Stimulating-the-Market-Growth.html
https://www.foodnavigator.com/Article/2018/05/04/There-is-a-mega-trend-around-fermentation-The-rising-star-of-fermented-foods
Coton, Monika, et al. “Unraveling microbial ecology of industrial-scale Kombucha fermentations by metabarcoding and culture-based methods.” FEMS microbiology ecology 93.5 (2017).
Professional Kombucha Brewers Workshop, Barcelona (2019).
Jayabalan, Rasu, et al. “A review on kombucha tea—microbiology, composition, fermentation, beneficial effects, toxicity, and tea fungus.” Comprehensive Reviews in Food Science and Food Safety 13.4 (2014): 538-550.
Dutta, Himjyoti, and Sanjib Kr Paul. “Kombucha Drink: Production, Quality, and Safety Aspects.” Production and Management of Beverages. Woodhead Publishing, 2019. 259-288.

CFER Labs is your partner in food and drinks R&D. Obtain your free of charge workplan by clicking here.

Take a few minutes to search in yeast commercial suppliers catalogs and you will quickly find out the large number of different strains that are available for brewing beer and other beverages. Brewing yeast species were initially isolated from nature and later also domesticated in different parts of the world under different environments, which resulted in a variety of yeast strains with great physiological differences. The invention of the microscope had a key role on the initial identification and characterization of the different strains. Nowadays, the continuous development of microbiological and genetic tools along with new analytical techniques has contributed to a deeper understanding of the specific capabilities and limitations of each strain, as well as for the identification of novel yeast types.

Every year the number of fully characterized yeast strains increases and there are a few companies with culture banks that have a great variety of yeast strains: White Labs, WYEAST, Fermentis, Lallemand, Mangrove Jack’s, Imperial Yeast (organic) or CooLAB (organic), among others. In each website, you can find descriptions of each strain that will help you choosing the right strain for the intended beer type.

Start simple

If you are in doubt, start simple and brew with a yeast type which is a “work horse”, meaning that it will efficiently work for a great variety of beer styles. Still, there are some factors important to consider when choosing the yeast for alcoholic fermentation:

Attenuation – how much sugar can the yeast convert into alcohol. Usually, commercial suppliers divide the yeast strains in low, medium and high attenuation, varying from approximately 65 to 85%. The specific attenuation will impact not only the alcohol % but also the mouthfeel and flavor;

Flocculation level – how easy does the yeast cells settle after fermentation. This is an important feature when you wish to re-use the yeast to another fermentation. Besides that, a low flocculation yeast can lead to a lower attenuation, resulting in a worty flavor. On the other hand, if your yeast of choice has a high flocculation, the final beer will tend to be cloudier and you will be able to taste the yeast, like in weißbier or witbier;

Alcohol tolerance – alcohol level that inhibits and potentially kills your fermenting yeast. Choosing a strain that can stand the alcohol percentage you are planning to reach is extremely important, especially in those styles that require a high alcohol % such as Imperial Stout or Belgium Ale;

Temperature – each strain has a range of temperatures where it can grow, and it is important to know both the optimal and the extreme temperatures that the yeast can stand;

Metabolite production and sensoric properties – what kind of flavors and aromas are produced by the yeast strain. There are several metabolites (intermediates or final products of yeast metabolism) that can contribute to the sensoric properties of the finished beer: esters, carbonyl compounds, phenolics, higher “fusel” alcohols and fatty acids:

  • Esters are the resulting compounds from a reaction between an acid and an alcohol, and they are often associated with fruity notes in beer (e.g. ethyl acetate or isoamyl acetate). The specific types of esters formed, as well as their concentration, are strain-specific but the fermentation conditions also influence the ability of the yeast strain to produce them.  For instance, there are reports that high gravity brewing and high fermentation temperatures (20-25oC) result in higher levels of esters (as in some ale beer types).
  • More than 200 compounds with a carbonyl functional group have been found in beer, contributing for both its flavor and stability. Diacetyl and acetaldehyde are examples of carbonyl metabolites and probably the most “unwanted” compounds by brewers (except in some very specific beers), since they are considered off-flavors. Both the formation and conversion rates of those metabolites is strain-dependent, so the time that you will need to get a matured beer will depend on your yeast of choice. This is particularly important in large-scale production where time is a key control parameter.
  • Phenols are commonly associated with a medicinal or spicy aroma, and some specific types add astringency and/or bitterness in the finished beer. For instance, the earthy aroma present in Brett beers (fermented with Brettanomyces yeast) is directly linked to the formation of phenolic compounds.
  • When present in abundant levels, higher fusel alcohols, such as propanol and butanol, can result in fruity, floral and/or wine-like notes. Their formation can have a positive impact in ale beers but normally are not desired in ale types.
  • Fatty acids are essential elements in the yeast central metabolism, but they can also be broken down into staling compounds such as (E)-2-nonenal, which will give a “cardboard” character in the finished beer.
The presence of fermentation derived metabolites brings complexity to the final product, but in some specific cases they can also easily become overwhelming and give off-flavors.

In addition to the points mentioned above, when brewing at large-scale breweries there a few other parameters to consider when choosing the right yeast: stress tolerance, fermentation yield and productivity, mutation stability, among others. These are especially important for the re-usage of yeast in several fermentation cycles, which is a must in large-scale breweries to sustain the economical viability of the production process.

The number of identified and characterized yeast strains will increase more and more over the next years. I personally believe that some unique flavor profiles are yet to be found, and that will consequently expand the range of beer styles. If you are already brewing, what are your favorite yeast strains and how did you choose them? Tell us your yeastperiences in the comments below.

CFER Labs is your partner in food and drinks R&D. Obtain your free of charge workplan by clicking here.

Sources

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jib.49 
https://www.esa.org/esablog/research/spontaneous-fermentation-the-role-of-microorganisms-in-beer/http://www.wyeastlab.com/fermentation
https://www.nature.com/scitable/topicpage/yeast-fermentation-and-the-making-of-beer-14372813
https://www.whitelabs.com/
https://www.grainfather.com/blog/week-60-choosing-a-yeast-strain-for-your-beer/
http://www.equippedbrewer.com/equipment-and-supplies/how-to-choose-the-right-yeast-for-your-craft-beverage
https://beerandbrewing.com/how-to-choose-a-yeast-strain/
http://scottjanish.com/esters-and-fusel-alcohols/

 

A conversation where bacteria and fungi are mentioned usually triggers a red alert in our head since they are associated with some mean diseases. However, when we look back in history, the activity of yeast and bacteria were essential for our lifestyle, being the major responsible for many tasty foods and beverages that were and still are part of our culture.

Imagine a world without bread, beer, wine, cider, coffee, mushrooms, pickles…it would be for sure less interesting! It is estimated that there are one trillion different species of microorganisms on Earth, which shows the tremendous variety of bacterial and yeast species.

Beer fermentation is the process where the sugars coming from the malt are converted into alcohol and carbon dioxide by the activity of yeast and in the absence of oxygen. Traditionally, beer fermenting yeasts can be divided in two types: ale and lager.

 

The pre-activation of yeast, where multiplication and yeast mass increase takes place, is a fundamental step for an healthy alcoholic fermentation of wort

Ale yeast

In the old times they were defined as top-fermenting yeasts since their cells would be collected from the top of the fermentation vessel. The most relevant yeast is Saccharomyces cerevisiae (also called brewer’s and baker’s yeast) and it requires fermentation temperatures around 18ºC – 22ºC (64ºF – 72ºF). In comparison to a traditional pale lager, ale beers usually display a fuller body and more intense fermentation-derived flavors. In some cases, there will be a more dry and crispy character, which can give an unique combination to that beer.

In my opinion, the versatility of ale yeast is a strong advantage when comparing to the lager, which makes it possible to use for a large variety of beer styles: amber ale, brown ale, stout, porter and, one of my favorites, Indian pale ale. The traditional wheat beers from Germany (Weißbier) and Belgium (witbier) fall also in the ale category, where specific ale yeast types that give that nice banana and herbal aromas are chosen!

Lager yeast

The most common lager yeast is Saccharomyces pastorianus, which is a hybrid of two Saccharomyces strains. This means that its general characteristics are like those of the ale yeast but the optimal conditions for fermentation and the resulting beer will be different. Lager yeasts were defined as bottom-fermenting organisms because the cells were collected from the bottom of the tanks after fermentation. However, that distinction does not make sense in the current processes where conical vessels are used and both yeast types are collected from the bottom. Thus, lager yeast is currently associated with “cold fermentation” since it is done at temperatures between 7ºC – 15ºC (45ºF – 59ºF). This temperature slows down the metabolism of yeast which results in longer fermentation times.

Due to their lengthy fermentation and lagering period, the fermentation-derived flavors will not be as evident as in the ale types. The combination of malt and hops is the greatest contributor to the aroma complexity we can find in some lager beers such as the Dunkel Bock or the Saaz-seasoned Czech Lagers. Lager beer is the world’s most sold type of beer, being a fresh golden tone drink ideal to refresh the beer lovers like us.

Sour beers

In the recent years there has been a trend of intense flavors and aromas in beer, with high levels of bitterness but also acidity and sourness. The sour beers, where the lambic type is included, are made by spontaneous fermentation. This means that there is no controlled addition of yeast under sterile conditions, but you make usage of the natural yeast and bacteria present in the surroundings instead. In the old times, Belgium beers were all made in this spontaneous manner and it would take a few years to have a relatively stable beer production.

Among several types of bacteria and yeast, Lactobacillus, Pediococcus and Brettanomyces are the most relevant organisms for this kind of beer, producing acidity and giving that sour, dry and tart profile like sometimes you find in wine. Currently, it is possible to make this kind of sour beers in a more controlled way and you can even buy blends of these bacteria and yeast to produce a sour beer at home.

The variety of yeast and bacterial strains will increase more and more in the next years and many craft brewers are isolating their own blends of yeast and bacterial strains, which can give unique flavors and expand the range of beer styles. If you are already brewing, what are your favorite yeast strains and how did you choose them? Tell us your yeastperiences in the comments below.

Sources