In this guide, I will attempt to give broad recommendations regarding features and characteristics of espresso machines.  What makes one machine worth $200 and another $2000?  Read on to find out!

The Espresso Equation

Espresso is best produced when water of consistent temperature and pressure is extracted against evenly-ground coffee beans.  So therefore, the best espresso machine achieves this consistent pressure and temperature and produces the best coffee when and only when that water is introduced to the correct grind of coffee bean.

This begs questions - what is the correct temperature, pressure, and grind?  These are the variables that are subject to extreme scrutiny and debate.  Different machines produce different pressures and temperatures.  Water temperature even a few degrees off of ideal will make the espresso taste bitter or sour.  The correct grind depends on the filters in the machine - too large of a grind will produce underflavored and watery espresso, too small will produce a bitter taste and will clog the filter.  Experimentation is the only way to determine your personal taste, and this - to me - is part of the fun.

If you haven't already, read the wikipedia article on espresso machines - it explains terminology and gives an overview of the history of technologies.

Steam machines

The vast majority of espresso machines sold worldwide are steam based machines.  These machines boil water, then a one-way valve opens up and lets the pressurized water through the beans, which then drips through the portafilter ( the handle part where the grounds or pods go ) producing espresso.  This relatively simple process is flawed because the pressure and temperature is not consistent, the steam scorches the ground coffee which gives it a slightly burnt taste - however the machines are inexpensive and simple to use making them a great first machine to experiment with.

My Krups FND111 Allegro Espresso Maker ($60 list) (pictured above) produced latte's every day for a year until I graduated to a pump.

Pump machines

Pump machines use an electric pump to control the pressure and release of the steam and water, which in turn produces even pressure against the coffee in the portafilter ( the handle part where the grounds or pods go ).  This is the main reason why pump machines are more expensive and produce 'better' espresso than steam machines.  The water temperature and pressure is regulated and the water is heated either by a boiler or by a thermoblock.

Boilers are used in almost all commercial espresso makers, and produce very consistent temperatures.  Thermoblocks are blocks of very hot metal through which water is pumped or injected causing the water to immediately flash-steam producing pressure.  Thermoblocks are newer technology and purists very vocally reject them, citing that they may produce inconsistent temperatures because as water is injected into the block the metal will cool slightly, so the next injection of water will hit a slightly cooler block of metal.  I believe this theory is rational, but I also believe that the thermoblock design would not be widely used if it were not viable, so this is a question of personal opinion.  Machines that utilize thermoblocks are typically less expensive than boilers.

My Breville Ikon BES400XL espresso machine ($299 list) (pictured above) uses a boiler to maintain very consistent temperatures when brewing and steaming, and the pump system delivers consistent pressure to the pressurized portafilter.

Features that add to the cost

The materials the machine is constructed of also affect the cost of the machine.  Thermoblocks and Boilers made of aluminum or stainless steel are less expensive than marine-grade brass.

Most pump machines have a removable water tank, which let you brew and steam very quickly for multiple drinks before refilling.  Some machines hook up to the water line like commercial machines, so you never have to refill them.

Solenoid Valves control the flow of pressurized water and stop it from entering the brewhead when desired, so you can immediately pull another shot of espresso one after another - these valves add significant expense to the machine.

Steam wands can be adjustable and pivot-able, and most come with "frothing attachments" - I always remove these - you have to learn to froth milk one day, and once you learn it's so easy to make it just like you like it.

The portafilter can be pressurized or unpressurized.  Pressurized portafilters are forgiving.  They only allow the coffee to release from the portafilter once correct pressure has been reached within the brewhead.  Unpressurized or Nonpressurized portafilters allow for greater control for the experienced barista.  I've also read that pressurized portafilters will brew inconsistently-ground coffee more easily - this becomes important once you read the section on grinders.

Fully Automatic Machines

Fully Automatic machines have a hopper filled with whole coffee beans that they grind, measure, tamp, and brew at the touch of a button.  They often have automatic milk frothers as well.  These machines are very expensive, but they do everything automatically.

Grinders

As I mentioned, we need consistent pressure and temperature of the water, but also consistent grind of the coffee in order to produce ideal espresso.  Here's the hard pill to swallow:  You need a burr grinder to consistently grind coffee - and they are expensive.

If you like fresh ground beans, but don't want to spend the money on a quality grinder you have alternatives.  You can purchase pre-ground coffee from a dealer with a quality grinder - just make sure they grind it at the time of purchase, and try to purchase for a week in advance.  You can use your cheap grinder with a pressurized portafilter machine - because the pressurized portafilter is designed to brew at the correct pressure, the resistance from the grind becomes a non-issue - so grind consistency and tamping become less important to the taste.

Or throw in the towel and use Pods: Many machines accept ground coffee or pods, which are pre-packaged coffee in teabag-like disks.

If you are serious about the quality of your espresso, and you are trying to replicate the coffee-house experience, you must spend the money on a quality burr grinder and figure out the ideal grind settings for your machine.

Common Complaints

Almost all of the negative machine reviews that I've read online complain about issues that center around technique, not around features of the machine.  For example, one may read "this machine produces bitter-tasting coffee" - well, that is not a problem with the machine, it's a problem with the grind or type of coffee you are using!  Keep that in mind when reading reviews: is there a problem with this machines' ability to produce steam, or do they just not know how to froth milk?!  What is this persons' experience with espresso makers?

Each machine is different, so even if you are an expert at producing your favorite drink with one machine, you will have to adapt your technique and materials to another machine - there is a learning curve, and again that's part of the fun - learning how to use your machine to make the best espresso!  Reviews that start out stating they opened the box and plugged it in and were not satisfied with their first shot, I wouldn't expect them to!  Remember these machines are tools, not factories (except for the fully automatics)!

My favorite complaints center around cleaning - "milk dried all over the steaming wand!".  You must clean your machine after each use - it's very easy when you make it a habit and trust me, cleaning fresh milk is much easier than cleaning dried milk!  You also have to decalcify the machine periodically with a solution of water and vinegar.  If you don't wrinse out your filters, they will clog.  Empty out the spill tray or it will get nasty, just like any other standing water in your house.  Don't you dare blame the manufacturer for these things!  These people must write to oven manufacturers to complain about how the oven burned their turkey dinner, then didn't clean up after itself!

Recommendations

Steam machines are basically all the same - get one that looks nice with solid controls - I love my Krups.  When I graduated to my pump machine, I wanted the consistency of a boiler and the convenience of a pressurized portafilter, because I wasn't going to spend the money on the burr grinder  - I'm very happy with my Breville Ikon.  If money was no object, I'd get a burr grinder and a Rancho Silvia - widely recognized as the best reasonably-priced home machine on the market.  I wouldn't get a fully automatic machine - I don't like the idea of not being able to tweak the taste of the coffee.

A note regarding personal taste...

I'm assuming that you are reading this article because you enjoy espresso or espresso-based drinks, and you are thinking of purchasing a machine to make them at home.  In the end, the machine should be easy to use and enable you to produce drinks that you enjoy.  It's easy to get caught up in the endless array of functions and extras these machines offer - get one that has features you think would be nice and useful, that might look good in your kitchen, and then take the time to learn to use it and clean it properly.  Enjoy your coffee!