5 Roasting Coffee at Home
  5.1 Why roast at home?
  5.2 What do I use to roast?
    5.2.1 Commercially-made home coffee roasters
    5.2.2 Notes about roasting
  5.3 About green beans
    5.3.1 Storing green beans
  5.4 What is the process?
    5.4.1 What's the Maillard reaction?
  5.5 Degassing, resting, and storage

5.1 Why roast at home?
a) This FAQ has repeatedly stressed the importance of bean freshness. Coffee stales quickly; overall, you want beans that were roasted anywhere from one day to about a week and a half later—two weeks if unground and stored properly. Home roasting is an excellent option if you do not have access to freshly roasted beans.

b) A starter home roasting setup can be had for as little as five dollars (in the form of a used hot air popcorn popper from a thrift store), or twenty-five dollars for a better setup using a new popper and a outdoor grill-type thermometer. Green beans typically sell for quite a bit less than quality roasted beans (often, three to six dollars a pound, averaging somewhere in the four dollar range).If you graduate to a dedicated roasting device, the price can leap to a hundred-twenty to a hundred fifty (and up), but amortizing that cost over the roaster's life and coupled with the lower bean price, you will at the very least break even.

b) Under reasonably proper conditions, green beans can be stored up to at least a year without a loss of quality, allowing you to keep multiple varieties on hand. These can be mixed and matched to create custom blends, or simply sampled country-by-country. Since green beans can be held in stock for so long, some retailers offer a far larger variety of beans than those selling roasted beans, even a few dozen or more countries and multiple varieties from each nation.

c) Even with basic experience, you can get better quality coffee than the stale beans you've grown used to; many new home roasters are amazed at the quality of their coffee even after one or two roasts. More importantly, you can learn to roast your coffee exactly how you like it: to what degree and with what blends.

5.2 What do I use to roast?
Regardless of the method chosen, be aware that roasting produces significant quantities of odorous smoke, which increases with degree of roast, as well as fine chaff that has a tendency to fly all over the place.

At its most basic, you can roast coffee beans in a skillet or wok, constantly mixing to prevent burning. However, this is a somewhat tricky practice, and it is difficult to produce consistent results. A modified version of this technique is to use an old-fashioned stovetop corn popper, which basically consists of a deep saucepan topped by a lid fitted with a stirring paddle turned by a handle. Like the basic stovetop method, the popper requires that you continually stir the coffee as it roasts. Many people have successfully used convection ovens. Note that due to their round shape, peaberries are easier to use with these manually-stirred methods.

Perhaps the most commonly used item not specifically designed for roasting is an hot air popcorn popper. These devices are easily found and inexpensive; some home roasters scour thrift or charity shops for favored models, or just to be able to buy them for a few dollars apiece. Three to four ounces of green beans (by weight) are poured into the popper, which is then turned on. The beans should start moving around, though some manual stirring may be needed until they begin to lose moisture and are able to move on their own. The beans will pass through the various stages of roasting, as described below.

Just before the desired degree of roast is reached, pour the beans into a metal sieve or colander and toss between two sieves to cool. Alternately, pour them out onto a large, heavy cookie sheet; it will help if you can pre-chill the sheet. With either method, a fine spray of water may be used to speed cooling, though many eschew wetting roasted coffee.The water must be used sparingly: you want it to evaporate immediately and not remain on the beans, so a couple of quick sprays with a mister will suffice.

You can vary the roasting profile by varying the quantity of beans you roast: the more beans you use, the darker the roast—more specifically, the faster the beans will roast. If you mount a grill thermometer so that the tip sits in the beans during the roast, you will be enable to more finely control the degree of roast and consistency between batches; using a timer will also further these goals. The thermometer must be able to read up to 500 degrees (though coffee roasted to that upper limit will be charcoal).
The standard recommendation is to use a popper that feeds the hot air in from vents on the side of the popping chamber rather than the bottom, for fear that debris that falls down through the vent holes may catch on fire. This may in fact be an erroneous fear, but since following the recommendation costs nothing, it may be best to heed this warning.

5.2.1 Commercially made home coffee roasters
The most common home roasters, as well as the hot air poppers, are known as fluid bed roasters, since they roast on a "bed" of hot fluid: air. The basic principle is the same as the popcorn popper, i.e., blowing hot air up through the beans, but they have built in timers, a cooling cycle that automatically cuts in after the roast, and a chaff collection device at the top. Current models include the Hearthware i-Roast 2, the Fresh Roast Plus 8, and the Zach & Dani roaster. The iRoast is the newest of the roasters, and the most programmable of the lower-cost consumer models. Almost as new is the Zach & Dani roaster, and its most revolutionary aspect is that it appears to have addressed the smoke issue with a built-in catalytic converter. Although it adds a mixing auger, it is basically a fluid bed roaster. The Fresh Roast Plus and Caffé Rosto are popular models with their own advantages and disadvantages.

The Alpenröst by Swissmar uses a fundamentally different method of operation. Rather than using hot air, the Alp (as it is often called) uses an electric element to heat a rotating drum that holds the beans. Many pundits assert that drum roasters produce a roast with more body than is possible with a fluid bed roaster. The Alp also roasts up to twice as much as the other devices—up to a half-pound at a time. At the time of this writing, the Alp is no longer made.

There are two "prosumer" drum roasters currently in production. One is the HotTop, made in Taiwan. It resembles a miniature commercial drum roaster; March 2007 model prices are US$980 (older models are hundreds less). The other is the Gene Cafe, which typically sells for US$495.

The implication of the prosumer devices is that the roasting process is now automated; however, although much of the work has in fact been reduced, it still very important that the user monitor the process. These machines are affected by too many variables—ambient temperature, line voltage, difference in the beans themselves—to the extent that a specifically desired result cannot be taken for granted.

There are some discontinued roasters that still popup in online marketplaces, in thrift stores, or "brick and mortar" warehouse-type stores.. The Hearthware Precision, actually a successor to the Gourmet, was one of the biggest sellers, but was many users experienced reliability issues. West Bend, perhaps inspired by the use of their popcorn makers by coffee roasters, brought out a roaster that was almost immediately discontinued, so the available information on this machine is limited. In the mid 1980s, Melitta sold the Aromaroast, but this machine was finicky at best and often could not raise the beans to roasting temperatures without user ingenuity. The Aromaroast sometimes turns up for sale, but it is best avoided. Unimax (later Royal Max) sold an expensive half-pound roaster, but the company has folded. The Caffé Rosto was a machine that produced coffee praised for its body, but was often described as being overly sensitive to household current fluctuations.

Rotisserie-style drum roasters, made to be fitted to outdoor grills, can be found online, and many home roasters configure their own from off-the-shelf parts. These devices can roast a pound or two at a time.

5.2.2 Notes about roasting
One of the largest drawbacks of the home roasting devices is that they produce smoke; often enough to set off smoke detectors throughout the home. As such, it is imperative that you either roast outdoors during warmer temperatures, or use adequate, fan-powered venting to the outdoors during cooler weather. Range top hoods may be effective, but they must draw sufficient air, and the roaster may need to be raised up closer to the hood. The higher the capacity of the roaster, the more smoke it'll produce.

With any method, chaff is an issue. Chaff is a light, thin "skin" that covers the processed, unroasted beans. During the roasting procedure, it separates from the bean and becomes a light, delicate nuisance. A popper will blow it out onto whatever surface or container sits outside of its vent mouth. A home roaster will have a chaff collector built in which, like a dryer's lint collector, needs to be emptied after each use. Inadequate chaff removal plagues many home roasting devices; since the chaff will give your brewed coffee a grassy taste, you should try to make sure that as much chaff is removed as possible. This may involve pouring the beans back and forth between colanders, or fiddling with the roaster's cooling cycle.

The total roasting process takes from 5 to about 25 minutes depending on the type of machine, with the popcorn roasters normally taking the shortest time — and yielding a more acidic, brighter-tasting cup with less body — than the other methods.

5.3 About green beans
The simplest way to purchase green beans is to look for a local roaster; many will be happy to sell you unroasted beans. Unroasted beans should be anywhere from fifteen to forty percent less expensive than roasted beans. If the retailer charges the same price for green that they do for roasted coffee, go somewhere else—you're being taken advantage of, considering the seller's savings on roasting costs and the weight loss inherent in roasting (almost twenty percent of what they're selling you is water, so your pound of green coffee will translate into about thirteen ounces roasted).

There are various sources on the Internet for unroasted coffee, and many have an almost awe-inspiring selection.

Checking the alt.coffee archives for names of mail-order roasters will be quite fruitful; some companies have made names for themselves by virtue of the excellent quality of their beans. There is little point in going through the effort of home roasting if you purchase inferior beans. Sometimes, unscrupulous distributors or retailers will substitute cheaper beans for more expensive or hard to acquire varieties, so a reputable dealer is important.

Look for suppliers with specific designation of origin: for example, "Ethiopian Harar" or "Ethiopian Sidamo" rather than just "Ethiopian." Even better, some suppliers will tell you the farm or estate on which it was grown, or the name of the importer. This will enable you to more effectively compare beans, and may also indicate a retailer with respect for his customer and dedication to the product. The trick with green beans is that even the products of a specific farm can change from year to year, largely depending on reasons from that year's weather. Retailers who provide "cupping" reviews of individual offerings are particularly helpful, and they may note that the newest crop from a particular estate has changed from the previous crop; perhaps it's better, maybe worse, or maybe just different.

5.3.1 Storing green beans
Processors and importers store their unroasted beans in cloth (or plastic mesh) bags in cool, dry, and dark locations, with good air circulation. Storing unroasted coffee in airtight plastic is a special issue. Unroasted coffee does best in moderate humidity, mild temperatures, and ventilated storage conditions. If you have these conditions, then storing the beans in breathable containers should work well. However, sealing the beans in airtight plastic may well be superior to exposing them to humid storage conditions, especially if you are able to vacuum seal the container. For general conditions, the average person should be able to simply store their green beans in airtight plastic.

5.4 What is the process?
Unroasted beans are generally light green, although monsooned and decaffeinated beans will have different colors. After the first few minutes of roasting, the beans begin to turn yellow, then a very light brown. When bean temperature approaches 380 degrees Fahrenheit, first crack occurs, so called because various structural changes cause the beans to make a sound similar to that of corn popping. It is at this point that the beans begin to be usable for brewing coffee, but the taste will be poor. First crack continues for approximately a minute (or longer, with large drum roasters), and chaff begins to separate from the bean.

The beans will continue to darken as the sugars caramelize, passing through roast degrees common for commercially distributed coffee in North America. When the bean temperature reaches about 435 degrees Fahrenheit, second crack occurs, similar to the sound made by Rice Krispies® after milk is added. At this point, oily patches will become discernable on the bean surface and, mainly when using poppers, small discs (homeroasters often refer to these as "divots") will begin to fly off of the bean surface. As roasting continues, the beans will become darker, and the their surface oilier. Coffee at these advanced stages is typically used for espresso, and for brewed coffee in Italy and France. Bean temperatures around 480 degrees Fahrenheit represent the upper end at which coffee is palatable, and even before that, it will be too dark for many people.

Until you can readily judge bean color, keep a sample of your target roast handy, for comparison purposes. Keep in mind that ground coffee will have a somewhat different color than whole bean.

The beans lose up to twenty percent of their weight upon roasting, due to the loss of moisture. However, they also expand, so the now-lighter batch will take up a greater volume.

5.4.1 What's the Maillard reaction?
Distinct from caramelization, this refers to a non-enzymatic browning caused by a reaction of simple sugars and amino acids. With first crack, the bean actually undergoes an exothermic reaction (it gives off more heat than it takes in). This step is crucial in the production of desirable flavor and aroma compounds.

5.5 Degassing, resting, and storage
Roasted beans give off a considerable quantity of carbon dioxide in the day following roasting; this emission continues at a reduced level over the next two or so weeks. This can serve as an indicator of bean freshness: just-roasted beans will create a goodly quantity of froth in a cafetiere, whereas stale beans will create almost none. In the coffee trade, this particular froth is called "bloom."

Roasted beans are at their best anywhere starting from four to twenty-four hours after roasting, depending largely upon the variety of the bean and the degree of roast. Some varieties, notably espresso blends, are at their best thirty-six to forty-eight hours after roasting. This process (holding off on brewing for a specific period) is usually called "resting." The mylar/plastic bags with one-way valves are one favored method of storage for resting; some home roasters have rigged-up jars with one-way valves. At least in theory, tightly sealed containers without valves may deform or shatter as a result of the buildup of gas pressure.

The beans should be kept away from oxygen; the degassing process will help protect the beans from oxygen.

If you roast in smaller quantities, you can keep several batches available at once, optimized for different purposes, such as regular for the morning, a decaf for evenings, and an espresso batch.

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