Technical Focus Brewlab’s Dr Keith Thomas considers sediment

Should I drink the sediment from a bottle?

Brewlab’s Dr Keith Thomas looks at the science behind bottle conditioning and the makeup of the sediment common in this style of beer…

Should I drink the sediment? Possibly – but before considering whether bottle sediments are beneficial let’s take a quick look at the bottle conditioned market. With the reintroduction of CAMRA “Real Ale in a Bottle” accreditation, there is an opportunity to promote this now specialist niche of beers and emphasise the features of a simple but challenging technology. Rather than relegate their identification to “May contain sediment” a bold labelling of “Bottle Conditioned” may enhance sales – and qualify claims of “Traditionally Brewed”. Just to emphasise the features of bottle conditioned here are some of the specifications. Put simply it is a “beer which undertakes a secondary fermentation in the bottle”. This implies that the beer contains living yeast and enough sugar for fermentation and production of carbon dioxide. Arguably it also produces additional flavour and, because of growth, an increase in yeast. While bottle conditioning is readily and simply achieved by bottling beer directly from fermenter without filtration or added carbonation it requires a sound understanding and management of fermentation theory. The challenge is to ensure that the right level of sugar is present to achieve a suitable carbonation, that there is enough yeast in good condition to conduct the fermentation and a suitable temperature and time balance during the maturation. Achieving success requires experience and awareness of how problems develop. If the primary fermentation is incomplete excess sugar may be present resulting in overcarbonation. In contrast, complete primary fermentation results in under-carbonation as few sugars remain – unless suitably calculated priming sugars are added. If the yeast has been stressed it may ferment poorly to produce off flavours and if contamination is present the alcohol may be converted to acids. All these features require attention and skill to avoid, and of course apply equally to can conditioned beer. Moreover, we have the recent concern of contaminating diastaticus yeast which produce enzymes to digest dextrin sugars resulting in a gushing beer. Bottle conditioned beer is not an easy option. Returning to definitions it should be distinguished from hazy or cloudy beer which may also contain yeast but may well be pasteurised or bottled with additional carbonation added or even, in some wheat beers, contain added protein. Aside from being a demonstration of technical skill, and possibly having a more mature flavour, does bottle conditioned beer contain any specific benefits? The main focus here is on possible beneficial effects of yeast, although the beer may have a higher level of protein and polyphenols from a lack of filtration. For yeast we would look to probiotic properties, a feature of many fermentation microbes and an active topic in many health food promotions. The elements of probiotic action are to provide protection against potentially harmful microbes, particularly pathogens but also to enhance your immunological health and promote growth through increasing nutrient uptake. The features providing protection include antagonism between microbes, ability to block surfaces in the digestive system from pathogen access, production of protective fatty acids and of organic acids particularly lactic and acetic. Taken together these actions are claimed to counter diseases, particularly infective ones but, possibly enhance body reactions to non-contagious diseases such as cancer. The most promoted microbes meeting these criteria are in the lactic acid and the Bifidobacteria groups. Until recently the only yeast with probiotic properties was Saccharomyces boulardii – a member of the Saccharomyces genus. This is not a species typically used in brewing but has been identified in historic samples of beer. Nevertheless, the potential of other Saccharomyces and non-Saccharomyces

brewing species being identified as probiotic is an active area of research. To be recognised as probiotic a microbe requires more than the characteristics noted above, most particularly the ability to survive in high numbers at delivery and after ingestion so as to be active at the relevant location in the body – generally the large intestine. In fact, a definition of a probiotic as “live microorganisms that when administered in adequate amounts confer health benefits on the host” implies numbers are important. A daily intake of 1000 million cells is recommended as many cells may die before they reach the large intestine. Applying this to the sediment in a bottle conditioned beer requires an analysis of yeast numbers but typical levels at bottling are up to one million per ml. These will increase to some extent during secondary fermentation, possibly doubling to two million per ml. A 500 ml bottle could thus contain 1000 million cells – in effect a daily dose if all remained viable. Of course, sour beers brewed with bacterial and yeast fermentation will also contain bacteria probiotics and have greater potential. So, should you drink the sediment? Well although brewing yeast isn’t recognised as probiotic at the moment it has potential and as a source of nutrients won’t be harmful. It may, however, affect the flavour of your beer if suspended so probably best to reserve as quick glug after your pint or saved to savour later. As research develops brewing yeast may be identified as having more distinct probiotic effects in which case bottle conditioned beer will have greater attractions for promotion. Draught servings may also change. Imagine asking the bar staff for a serving of cask residue rather than complaining about a cloudy pint!