The extraction is stopped when the espresso is deemed complete. Some machines will do this automatically by measuring the volume of water that has been pumped through the group head. Next-generation espresso machines feature built-in scales that measure espresso weight, allowing the barista to calculate extraction ratio between beverage weight and ground coffee weight accurately on the fly. Some baristas still prefer to do things manually, believing that every shot presents itself differently and requires a certain degree of reactive nurturing. I remain an advocate of programmable buttons, with a dependable response that is specifically tailored to the needs of the individual coffee, dose and grind.
UNdER PRESSuRE
Pressure is not something that most people need to worry about when making espresso. Most machines are set to the standard 9-bar/130 psi of force and will merrily go about their way. Some modern espresso machines are tackling pressure head-on, though, with the function to adjust pressure through the course of the brew. This adds another parameter to the espresso process, which for many means yet another concern on an already long list of concerns. But if your caffeine tolerance allows it, tinkering with the pressure profile can help to finely tune an extraction to a level of precision that opens up new realms of deliciousness in the cup.
A bottom-less portafilter reveals a beautiful, if a little surreal, espresso extraction in full flow.
The pressure of the water that is forced through a coffee bed determines the contact time with the coffee in the filter basket. Very low pressure would mean long contact time, and very high pressure a short contact time, but the exact time of contact is also a function of the dose and grind, too.
Having the ability to ramp the pressure up (or down) near the end of an espresso brew affords the barista increased powers. What this all boils down to depends largely on what you are hoping to get out of the espresso. A larger-volume drink made at lower pressure with a coarser grind could be just as balanced and tasty as a shorter-volume drink at high pressure made using a finer grind. They would be two quite different drinks, mind you.
CREMA
For many people, the tan-coloured foam that sits on top of an espresso is an intrinsic part of the espresso experience. But the reverence that it commands is perhaps equalled by its misinterpretation as a gauge of quality. To understand why that is, we must first get to grips with what crema (Italian for ‘cream’) actually is.
In all brewing methods, water will extract some amount of carbon dioxide from ground coffee, and this is apparent in the bloom that we see in pourover brews (see pages 124–133). A dense mound of crema is only possible due to the high-pressure nature of espresso brewing, however, where concentrated carbon dioxide is forcefully extracted from ground coffee beans. The sudden decrease in pressure when the first seething red drops of espresso emerge from the spout causes the dissolved carbon dioxide to inflate into larger bubbles very quickly, expanding the volume of the drink so that the cup appears to fill faster than the rate of flow could physically allow. Bubbles are all well and good, but they would be lost immediately without something to stabilize them; that something is a surfactant (a naturally occurring substance that lowers the surface tension of a liquid) in the form of a group of compounds called melanoidins, which are created as part of the Maillard reactions that took place during roasting (see page 55). Melanoidins crowd around the bubbles of carbon dioxide, increasing the bubbles’ surface tension and strengthening them into a fairly stable foam. It’s no coincidence that an espresso looks so similar to a pint of Guinness when it settles – the bubbles in the stout are stabilized by melanoidins, too, which are formed during the barley-roasting process.
Leave an espresso to sit for long enough and you will eventually notice that the crema begins to dissipate. This is a character trait that is consistent among all foams, where the liquid part of the foam begins to drain away. It’s possible that the rate of drainage (or the tenacity of the crema) can be used as a rough indicator of quality in espresso, since properly extracted shots are generally awarded with a longer-lasting crema. Indeed, an under-extracted shot of espresso generally features less crema and the little crema it does have it loses at a faster rate. This is a result of the faster extraction, over a shorter period of time, in which less carbon dioxide is drawn out. Less crema is also found on older (stale) coffee, which has much less carbon dioxide to give. It’s for this reason that I would always question an espresso featuring very little or no crema at all.
1
Crema fills the glass during the first half of espresso extractions, as carbon dioxide inflates its proportions.
Another thing that crema is useful for is gauging the strength of the drink. After all, the liquid part of foam is nothing more than a network of the same coffee that sits below it. It is much paler, of course, because of the way that light refracts through the bubbles, but it is a representation of the drink’s colour, and therefore strength, nonetheless.
2
As the finished espresso begins to settle, the crema floats, then begins to drain away into the drink below.
3
After a minute or so the gas has mostly dissipated, depriving the drink of some of its volume in the process.
There has been some suggestion in the past that crema acts like a kind of security blanket that prevents the escape of volatile aroma molecules. Studies conducted by Nestlé on this topic found that the opposite is actually true, and that in the first few minutes of an espresso’s life, the multitude of bursting bubbles, which make up the orange mass of soft crema, actually promote the propulsion of aroma molecules away from the drink. While this might appear like something of a win for the crema-lovers out there, we need to ask ourselves whether or not we would prefer our aroma molecules floating around above our drinks, or held back for better enjoyment in the mouth.
In my experience, crema, by itself doesn’t taste particularly nice, and I’m not alone. Certain factions of the speciality coffee industry have instigated a crema rebellion (or as I like to call it, crembellion) that has seen some extremists take to spooning off their crema before drinking their espresso. I find this kind of thing to be a little severe, however; in clinical trials, crema has been found to improve the perceived ‘smoothness’ of an espresso in both its appearance and the benefits to mouthfeel that it offer. I think it’s vital that we view crema as more than just a taste contributor, and as a player in the broader multisensory appeal of espresso.
ESPRESSO AND MILK: A MATCH MADE IN HEAVEN
07
INTRODUCTION
A shot of espresso on its own is not to everyone’s taste. It’s a potent little package of flavour that can sometimes benefit from the tempering effect of milk. Espresso and milk are a great match, too – the fruit, caramel and chocolate qualities of the shot play nicely with the wholesome dairy flavours of the milk, lengthening out toffee, chocolate and dried fruit into an indulgent sipping beverage. For many people, the combination of espresso and milk makes a satisfying substitute breakfast, supplying morning calories as well as essential minerals.
The range of espresso and milk marriages is a wide one, from a splash of espresso in a milkshake through to a blob of milk foam or a coating of milk inside a glass to take the edge off a naked shot. Many of the coffee drinks served in cafés today contain far more milk than coffee. Indeed, some coffee-shop chains have become exceptionally good at masking the flavour of their coffee with, quite frankly, disturbing quantities of milk and additional, usually sweetened, flavourings. But even in the best cafés milk plays a big part in the quality of a cup, both as a delicate and nuanced ingredient and as a medium for controlling the temperature of the drink.
Espresso is not the beginning and end of it all, however. It might surprise you to know that we’ve been mixing coffee and milk for around 300 years. In this section I will describe how these drinks came into existence, why there is such a powerful affinity between the coffee bean and the cow, and how to produce some of the world’s favourite espress
o-and-milk drinks.
HISTORY
Coffee and milk or cream have long been seen as natural companions. It was early in the 18th century that the practice of combining them began, but, rather than being enjoyed for its own sake, the drink was regarded at the time as the preserve of children, the elderly and the sick. Mixing milk with tea was established around the same period and for similar reasons. Feeling under the weather? Put some milk in your coffee. Adding cream to coffee was the next step towards creating a more indulgent drink.
In 1727 an English historian, named James Douglas, wrote that many people had an aversion to the intensely bitter taste of black coffee, preferring to have ‘mix’d it with either sugar or milk’. Tristram Shandy, the hero of Laurence Sterne’s eponymous comic novel published in the 1760s, notably drinks ‘two dishes of milk coffee’, remarking that the beverage ‘is excellently good for a consumption, but you must boil the milk and coffee together – otherwise ‘tis only coffee and milk’.
To my mind, boiled milk is rarely tasty and, despite these questionable early attempts to invent the latte, the harmonious pairing of coffee and milk didn’t truly occur until the espresso machine was well established in the mid-20th century.
Milk became the companion of the espresso machine for three very good reasons. Firstly, there is the advantage of being able to do two tasks – hydration and caffeination – at the same time. Warm milk can be mixed with hot espresso to create a beverage that slips down easily and provides a pretty good breakfast-in-a-mug for those in a hurry. Next, there is the fact that milk reduces the temperature of the drink slightly, especially in the case of latte served in the traditional Italian way, meaning that the drink can be quaffed with little risk of burning your mouth. Finally, there is the financial angle. Handing over a pocketful of change for 25 ml/1 fl. oz) of something that provides little more than caffeine and flavour can be a little galling. If you lengthen the drink so that it is something to be sipped and savoured, you have a better commercial proposition. Coffee becomes less of an in-and-out, leaning-on-the-bar affair, because the drink takes longer to consume, and the café selling it also has a better chance of selling suitable accompanying foods such as pastries, cakes and doughnuts. Espresso-and-milk drinks benefit everyone.
TYPES OF MILK
Milk is an emulsion consisting of fat globules and a mixture of minerals, proteins, acids, sugars and salts. It is stabilized by the whey protein beta-lactoglobulin, which traps fat globules and suspends them in water. The mixture of fat and water is what makes milk opaque; the emulsion refracts the light and makes the milk look cloudy.
The milk you drink has almost certainly been pasteurized. If it hasn’t, you probably live on a farm. Pasteurization kills 99.999 per cent of bacteria, lengthening the shelf life of the product from three days to around three weeks. In the standard pasteurization method, known as HTST (high temperature, short tIme), the milk is rapidly heated above 72°C/162°F for 15 seconds to kill the bacteria. Pasteurization has some disadvantages. It destroys some of the whey proteins in the milk, for example, and reduces mineral content.
‘Long-life’ or UHT (ultra-high temperature) milk is heated to a whopping 135°C/275°F for two seconds, using jets of blazing-hot steam and vacuums to cool it down. UHT milk has become very popular in Europe (with the UK being a notable exception), but I regard it as vastly inferior to ordinary pasteurized milk.
Some milk is micro-filtered, whereby the cream is separated and pasteurized independently. The whey (watery part) is pumped through tiny apertures that filter out the bacteria spores, and the cream is mixed back in afterwards. This method is slightly less effective at removing harmful bacteria, but more of the milk’s natural mineral and protein content is preserved.
Many milk brands are homogenized, too. This process involves firing the milk through very thin pipes, causing the fat molecules to break down and become smaller. The protein in the milk does the job of holding these smaller molecules in place, sustaining the emulsion, and the result is a silky-smooth milk that is not prone to separation, albeit with a slightly blander flavour that its unhomogenized counterpart. I’m not particularly old, but I can still remember having unhomogenized milk delivered in bottles in which the neck had became blocked with the separated cream component.
Whole (full-fat) milk has long been my preference for a cappuccino, latte or flat white. The extra fat in the milk gives the drink a slightly more silky consistency and glossy appearance, which is more than apparent on the palate, and a richer flavour. However, as is normally the case, the tastiest option is often the one condemned as being bad for you. For those concerned about fat content, skimmed and semi-skimmed flavours are available, but I have always considered the loss of quality too great a sacrifice for the sake of a gram or two of dietary fat.
Clouds in my coffee, as a turbulent splash of cream drowns in a dark pool of coffee.
Whole milk contains between 3.25–3.5 per cent fat, while skimmed/skim has about 1 per cent. A typical latte requires about 150 ml/5 fl. oz of milk, meaning that a full-fat latte has about 5 g/1/6 oz fat and a skimmed latte 1.5 g/1/18 oz – a 3.5 g/1/8 oz difference per serving. To put it in context, a 150 g/ 5 ¼ oz bag of nuts has around 70 g/2 ½ oz of fat, equivalent to the difference between 20 full-fat and skimmed lattes. Furthermore, new studies have found that the less your milk is tampered with, the better it is for you, regardless of fat content.
Some milk is naturally low in fat. In New Zealand, cows have been selectively bred to produce milk containing 1 per cent fat straight from the udder. Other studies have challenged the conventional belief that fat is bad for us and concluded that the traditionally accepted notion that high-fat diets lead to a greater risk of heart disease may be wrong.
STEAMING MILK
Correctly steamed milk is a fine combination of microscopic air bubbles and warm liquid with a sweet flavour and a light texture. Overheating or scorching milk is a depressingly frequent occurrence in large café chains; it can be identified by a burned taste in the coffee and, rather fittingly, plenty of screaming and rumbling noises emanating from the pitcher while the milk is being abused. Milk-based espresso drinks are not supposed to be scalding-hot, but there are plenty of stubborn coffee-drinkers – in the UK, in particular – who insist on their milk being at a magma-esque temperature, with no care for the resulting loss of flavour. The temperature of milk drinks is not simply about the perception of heat on the palate; it is both a creative and destructive force that must be monitored to maximize natural sweetness in the finished drink. Getting the right temperature is simply a case of not overheating the milk (70°C/158°F and above is bad news), serving the drink in a warm cup and drinking it quickly.
FOAM
In normal conditions, water and air don’t mix well. They need a surfactant to bind them together. When you whip cream with a whisk, the fat in the cream acts as a surfactant, a middleman between tiny air bubbles and the water that makes up the rest of the cream. As air is introduced through whipping, the fat in the cream stretches and the cream thickens; it becomes harder for the water in the cream to drain away because the mixture becomes much lighter.
Milk foam is held (for a time) by protein, not fat, in much the same way as egg white holds a meringue in shape. As the milk is heated, its spring-shaped proteins begin to unravel and denature.
There is barely enough protein in milk to sustain the foam and, compared to cream and egg white, milk foam is thin and watery. This makes it highly susceptible to drainage. Drainage involves the foam becoming lighter, until it is eventually only a super-light cobweb-type structure floating on the surface of the liquid. This process begins as soon as you finish steaming milk; it explains why, after being left to rest for a few minutes, a formerly creamy and consistent cappuccino starts to separate, leaving a light, foamy head on top and milky coffee underneath. For many of us, the ‘froth-layered-on-top’ cappuccino is the definitive cappuccino. But I can promise you that sipping a perfectly aerated cappuccino, whic
h has not yet had time to ‘split’, will avoid the embarrassing white moustache and bring far more pleasure to your tasting apparatus.
As previously mentioned, drainage is less of a problem with thicker liquids, which is why full-fat milk holds a better foam than skimmed. On the other hand, skimmed milk is easier to foam to begin with, since it contains less fat, which inhibits stability in protein foams.
HOW TO STEAM MILK
Always keep milk in the fridge. Obviously it stays fresher for longer when chilled, but starting with cold milk makes foaming much easier, simply because it gives you more time to ‘stretch’ or aerate the milk before it reaches the target temperature.
Use a clean pitcher. The exact shape and size of your pitcher is a matter of personal preference (and how many friends you have, of course), but thicker pitchers heat more slowly since the metal absorbs more of the heat. Use a clip-on temperature probe to monitor how much heat is going into the pitcher. Simple ‘analogue’ thermometers are fine, but I prefer to use an infrared probe because it reacts quickly and offers a digital readout. After plenty of practice, you will no longer need a probe to monitor heat; it can be done by listening and feeling alone (eyes aren’t much use here).
The intense swirling and stretching of the milk, as well as the controlled introduction of air, generates enough force to dissolve tiny air bubbles into the milk that will stay suspended for a short time. Properly aerated milk is often referred to as ‘micro-foam’, since the bubbles have been so closely integrated into the milk that they cannot be seen with the naked eye. Visually the milk will simply appear thicker and creamier. Try to avoid reheating milk; the proteins present in the milk don’t work as well the second time around, plus the flavour is not as good.
The Curious Barista's Guide to Coffee Page 14