Froth!: The Science of Beer

Froth!

Froth!

THE SCIENCE OF BEER

Mark Denny

© 2009 The Johns Hopkins University Press

All rights reserved. Published 2009

Printed in the United States of America on acid-free paper

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Library of Congress Cataloging-in-Publication Data

Denny, Mark, 1953–

Froth! : the science of beer / Mark Denny.

p. cm.

Includes bibliographical references and index.

ISBN-13: 978-0-8018-9132-8 (hardcover : alk. paper)

ISBN-10: 0-8018-9132-9 (hardcover : alk. paper)

1. Beer. 2. Brewing. I. Title.

TP577.D476 2009

641.6′23—dc       22 2008022646

A catalog record for this book is available from the British Library.

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covers are printed on paper with recycled content.

To friends from an earlier era—

John Hewitt, who taught me how to drink beer;

John Hardy, who taught me how to make it;

and my University pals, who taught me why

Contents

Acknowledgments

Introduction

One.   The Evolution of Beer

Two.   How to Make Good Beer at Home

Three.   Yeast Population Dynamics

Four.   Brewing Thermodynamics

Five.   Bubbles

Six.   Fluid Flow

Seven.   Final Thoughts

Glossary

Bibliography

Index

Acknowledgments

When I first pitched the suggestion of a beer-and-physics book to the Johns Hopkins University Press Editor-in-Chief, Trevor Lipscombe, he provided much encouragement. Later, during the fermentation stage, I was helped significantly by Horst Dornbusch, who influences beer and beerocrats on two continents, and who obtained for me special permission to raid the photo archives of the Bavarian Brewers Federation. The book has been brought into top condition at JHUP by copy editor Carolyn Moser and art director Martha Sewall. I thank you all.

In recent months my homebrewing has benefited from the generosity of John Rowling, who let me loose in his garden to pick hops. Cheers, John.

Froth!

Introduction

There can’t be good living where there is not good drinking.

—Benjamin Franklin (1706–1790)

There can’t be much amiss, ’tis clear,

to see the rate you drink your beer.

—A. E. Housman (1859–1936)

Beer is the most popular alcoholic beverage in the world. Estimates of worldwide annual consumption vary from 114 to 132 billion liters. Think of a lake 2 miles across and 30 feet deep.¹ Or, perhaps more apt, think of a giant beer glass half a mile high and a quarter mile across. I am talking about a lot of beer.

Before getting into the statistics a little more, I should tell you what this book is about. It may already have dawned on you that I am writing about beer, but there is more to my story than that. There are quite literally hundreds of books and Web sites about how to brew beer. Some of these are excellent (see the bibliography at the end of this book). Most fall into one of two categories, which I would characterize as How-To Plus a Lot of Recipes and Beta-Amylase Influence on Maltose Production from 2-Row Grain. The first category is self-explanatory and runs the gamut from excellent to awful.² The second category consists of ultra-technical accounts of the brewing process and seems to be written for professional brewers, academic researchers, or the geek end of the homebrew market. Both can provide interesting and useful information for the homebrewer, and some books (such as Wheeler’s Home Brewing) successfully combine elements of both categories. My book is unique, to the best of my knowledge, in that it unites brewing with accessible physics. You are not holding in your hands a recipe book or a Ph.D. thesis, but if you are interested in beer, and about how science and technology impact the production of your favorite tipple, then you will find much to engross you in the following pages.

Math analysis and beer tend not to go together in the literature. I am a physicist by training and a homebrewer by inclination. Inevitably I have, over the years, applied my knowledge of physics to the science of brewing. The results are, I believe, better brews and a better understanding of the brewing process. So, herein you will find out about beer and brewing in general, and about how to homebrew good beer, in particular. My science slant will be evident: math will occasionally be introduced, but the text is written so that, if you wish, you can glide over the equations without missing out on anything.

Mother Nature speaks mathematics, but most people don’t, so I am well aware that the text should be stand-alone. Those of you who happen to be interested in the math as well as the beer (and in my experience most mathematicians, physicists, engineers, and science students are partial to both) will find that the technical aspects of brewing lend themselves well to mathematical analysis. More about all that later: here, I would like to return to the statistics of beer, after a necessary paragraph about units.

In table I.1 you will find conversions between a few of the many and varied units that have evolved over time, and in different countries, for the measurable quantities used in making beer. The diversity of units can be confusing without such a handy table to effect a translation. Throughout the book, when I mention gallon I mean a U.S. gallon, which is not the same as an imperial (English) gallon. On the other hand, the physicist in me likes decimal units, and so I will perform calculations using liters, kilograms, degrees Celsius, etc. When I feel like it, I may convert to more familiar units in the text; otherwise, please remember the page number of table I.1 and refer back to it, if puzzled. All of the units in this table are used in the text. I have tried to reduce the information in table I.1—and the different units used in the text—to a minimum, leaving out, for example, some of the European units for alcohol content and some of the strange historical weights and measures, in particular the multitude of names for different bottles and barrels. Here is just one example to provide a flavor of the variety of beer and ale containers (wine is different): there are 54 imperial gallons in a hogshead, 36 in a barrel, 18 in a kilderkin, 9 in a firkin, and 4¹/2 in a pin. Of these units, only the barrel (abbreviated bbl) is widely used today in the brewing industry, though some retailers sell beer by the pin.

Table I.1 Conversion factors pertaining to beer

Now for some more of those telling statistics about beer. Per capita, the Czech people drain Beer Lake faster than any other nationality, as you can see from figure I.1. The nations that swill the most beer are listed in figure I.2. There are perhaps a couple of surprises that emerge from these two graphs.

Figure I.1. Annual per capita beer consumption by nation: (1) Czech Republic,(2) Ireland, (3) Germany, (4) Australia, (5) Austria, (6) United Kingdom,(7) Belgium, (8) Denmark, (9) Finland, (10) Luxembourg, (11) Slovakia, (12) Spain,(13) USA, (14) Croatia, (15) the Netherlands, (16) New Zealand, (17) Hungary,(18) Poland, (19) Canada, (20) Portugal. Source: The Kirin Brewing Co.

The presence of Spain and Portugal in the top 20 for per capita beer consumption may raise an eyebrow or two—except in Spain and Portugal. We might expect wine to dominate in these southern European countries, but, it seems, the Iberians like their beer as well. In fact, given the hot summers in that part of the world, and the chilled lagers brewed in Spain and Portugal, we can readily understand the appeal of a cool brew (ditto Australia, Mexico, and the United States).

The city which claims the greatest per capita consumption of beer is Darwin, in northern Australia. Here, a sweltering climate, a long tradition of beer drinking, and a macho culture combine to produce a beer consumption rate of 504 pints (233 liters) per person per year. That is about equal to 10 U.S. pints per week, for every man, woman, and child. Gulp.

Another surprise: the United States has been overtaken since 2004 as the top beer-guzzling nation. The taste for beer has reached China, and the world’s most populous country has now taken over pole position, as you can see in figure I.2. Worldwide, beer consumption has increased annually for each of the last 19 years due, at least in part, to increased summer temperatures. In the United States 87% of alcohol consumed is via beer. Forty-three percent of all the beer drunk is swilled by 10% of the beer drinkers. Consumption is not strongly correlated with income, but the type of beer consumed does vary with economic status. High-income earners are more likely to drink light beers or imported beers.

Figure I.2. Total annual beer consumption by nation: (1) China, (2) United States, (3) Germany, (4) Brazil, (5) Russia, (6) Japan, (7) United Kingdom, (8) Mexico,(9) Spain, (10) Poland, (11) South Africa, (12) Canada, (13) France, (14) South Korea, (15) Czech Republic, (16) Ukraine, (17) Italy, (18) Australia, (19) Colombia, (20) Thailand. Source: The Kirin Brewing Co.

Figure I.3. You may have drunk only one bottle of Belgian Duvel beer, but this is what you see.

Table I.2 The main beer-producing nations (output in millions of barrels)

In the chapters to follow, I discuss the different types of beer originating in different parts of the world. These various brewing traditions give rise to different strengths (alcohol by volume, or abv) of beer around the world. Thus, in England the beer and ale has an average strength of 4.4% abv, whereas in the United States (and most of the rest of the world), the favored lager style of beer is usually 5.0% abv. Belgium, with its own unique, bizarre, and delicious tradition of beers (e.g., fig. I.3), tops out with an average alcohol content of 8.0% abv.

So much for consumption: what about beer production? In table I.2 you can see the world’s largest contributors to Beer Lake. The United States still heads the table, but China is poised to take over the lead. The output of the traditional big producers of Europe (Germany, Britain) is static or declining as other types of beverage become more popular. In Russia a change in government policy (perhaps in a drive to reduce vodka consumption and alcohol abuse) and investment by foreign brewing companies has resulted in a big increase in beer production over the last decade.

Within the United States, 82% of beer is produced by three dominant breweries: Anheuser-Busch (52%), Miller (19%), and Coors (11%). The many and varied microbreweries are relatively miniscule, but increasing in number, for reasons that I will describe.

I hope that these bald statistics have gotten across to you the undeniable fact that the world likes beer, and likes it a lot. I am reminded of a drinking friend of mine from university days. Mikel said one evening, in a pub in Edinburgh, Scotland: I like drinking a lot! Succinct and to the point, you might suppose. Mikel, however, retained the scientist’s precision of thought even at that late stage of the evening and realized that his statement was ambiguous. Did he mean that he was very fond of drinking beer (we drank little else in those days), or did he mean that he liked drinking large quantities of beer? To provide clarification, Mikel stood up, perhaps unsteadily, and said: I like drinking a lot, a lot! Now I do not wish to be accused of encouraging alcohol abuse, but a little tongue-in-cheek humor is appropriate in this context, I feel.³

Despite the millions of Mikels in the world, however, all has not been well in the international beer community over the past 30 years or so. Many beer connoisseurs came to feel that the unstoppable increase in the size of big breweries was leading to a decline in beer quality. The reasons for this perceived fall-off in big-brewery beer, and the consequent flowering of microbreweries and of homebrewed beer, will be aired in the first chapter.

In chapter 2, I will tell you how I make my homebrew. To whet your appetite, please consult figure I.4. I have been brewing for about 15 years and have, by adopting a scientific approach (i.e., enlightened trial and error, plus some math analysis), pared the process down to the simplest possible method—though I continue to tweak the method with experimental refinements from time to time. I adopt the full-mash infusion approach and prefer the English style of beer (top-fermenting—e.g., IPA, mild, stout) rather than the continental European style of lager (bottom-fermenting—e.g., pilsner). My description will be placed in context, in that I will describe the main differences between small-scale homebrewing and large-scale commercial brewing, and between beer and lager brewing.

Figure I.4. There is nothing quite as satisfying on a hot summer day as one of these. One of the pleasures of home-brewing is that we can adjust recipes and techniques to customize a beer—to tailor it to circumstances and personal taste. So, for summer I brew a light-bodied, hoppy brew that retains flavor when refrigerated. My winter beers are darker and more full-bodied and are served at cellar temperature.

The third chapter describes a more theoretical approach to the study of beer. I will show how the population of yeast that is pitched into a batch of homebrew grows exponentially at first, and then suffers a catastrophic population crash as food resources are used up. There are practical consequences for the dedicated homebrewer that follow from this calculation, as we will see.

During the entire process of making beer, from mashing to bottling, the brewer is anxious to maintain the correct temperature. In chapter 4, I will discuss the importance of temperature control and share my calculations describing various aspects of beer thermodynamics, mostly from the perspective of a homebrewer.

Bubbles are very important to the esthetics of beer. They have been the subject of numerous scientific papers; research on this topic has even received an Ig Nobel Prize. Bubbles arise during fermentation, as well as during the pouring of a glass of beer, and they continue to rise (and fall) after the beer is poured and the froth has formed a head. All this and more in chapter 5.

Chapter 6 looks at beer as a fluid, rather than as the Amber Nectar, the Elixir of Life, the golden (or brown, or black, or even pink or orange) liquid worshipped by beerophiles.⁴ The distribution and dispensing of beer presents problems that have shaped the way beer is made and have also shaped the way that beer is presented to the connoisseur at public institutions dedicated to the appreciation thereof (pubs, to you). The final chapter takes a sideways glance at brewing as an application of science to everyday life. Many years ago an inebriated botanist once opined to me that it’s beer puts the fizz into physicists, and he may have been right.

So, this book is about the evolution of beer and the manufacture of beer on both large scale and (particularly) small scale. My story has a technical account—including math, which can be read around if algebra makes you squirm—of the many ways in which physics