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  1. Laboratory Methods (Food)

MPM: V-1. Beverages and Beverage Materials

Macroanalytical Procedures Manual (MPM) Main Page

A. Method for Coffee Beans (V-1) 

(1) Scope

This method describes procedures applicable to green coffee beans (modified as necessary for roasted beans) to:

  • Determine defects within individual beans due to insect infestation, molds, or other causes (expressed as percentages of reject beans by type and count)
  • Determine general contamination of a lot by insects, molds, rodents, or other causes, including foreign matter from spillage and sweeps
  • Determine defects which affect the quality grading of the lot, including defects within individual beans caused by deterioration, as well as contamination by extraneous matter

(2) Applicable Documents

  1. CPG 7101.06 Green Coffee Beans - Adulteration with Insects; Mold - Defect Action Level
  2. CPG 7119.04 Reconditioning of Imported, Insect-Infested Coffee Beans
  3. CPG 7119.08 Coffee and Cocoa Bean Sweeps
  4. IOM 631.1-631.12 Establishment Inspection, Sampling, Wharf Examination

(3) Defects

Defects may include coffee beans that are insect-damaged, moldy, contaminated by sweeps, or affected by various other sources of contamination.

  1. Insect Infestation and Damage -- The major pest attacking coffee beans is the coffee berry borer beetle, Hypothenemus hampei (Ferrari). The larvae of this pest infest the coffee "cherry" on the tree and burrow into the bean. Larvae, pupae, adults, and debris consisting of excreta and cast skins may be found in coffee. Another common pest that may cause insect damage, the coffee bean weevil (Araecerus fasciculatus (DeGeer)), is a broad-nosed weevil. In warm, damp climates, it is a storage pest of many seeds, including coffee. A green coffee bean can exhibit a variety of effects of insect damage, ranging from minor surface scars to major boring and tunneling. Minor insect damage is usually indistinguishable from mechanical damage and minor breakage. In addition to determining total percentage of insect-damaged beans, it may be useful to identify the species of insect that caused the damage. The damage caused by H. hampei and that caused by A. fasciculatus differ in appearance.
    Coffee Beans Damaged by the Coffee Berry Borer and the Coffee Bean Weevil

    Figure V-1: Coffee Beans Damaged by the Coffee Berry Borer and the Coffee Bean Weevil

    Photograph of undamaged coffee beans

    Figure V-2: Undamaged Coffee Beans

    1. H. hampei damage can be present anywhere on the bean's surface; the damage generally consists of the borer's exit and entry holes and tunneling within the bean. Bored holes are small, ranging from approximately 0.3 to 1.5 mm diameter, cleanly cut and circular. Surface damage is often surrounded by a blue-green stain (Figure V-1).
    2. A. fasciculatus damage may be present anywhere on the bean's surface and generally consists of bored holes that are less cleanly shaped and generally larger than the bored holes of H. hampei. Bored holes range from approximately 1.0 to 3.0 mm diameter and are caused by the insect's emergence from the bean. Irregularly-shaped surface damage, which is often large, is evident with extensive feeding (Figure V-1).

  2. Moldiness and Fungal Deterioration -- Moldiness in green coffee may occur during curing, drying, and storage periods, with the molds proliferating in natural folds and/or insect tunnels in the coffee berry. Water damage of bagged coffee may also promote the growth of molds on the beans.
  3.  Coffee Sweeps -- Coffee sweeps include sticks, stones, splinters, broom straw, paper, cigarette butts, chewing gum, and other diverse foreign matter.
  4. Contamination by Other Extraneous Material -- Other objectionable matter may be present in beans in an amount indicative of insanitary conditions or violations of good manufacturing practice. Examples include contamination from rodents, insects, and birds, or other defilements. Objectionable matter may be present as "sweeps" or from other sources.

    Quality grading of green coffee beans involves determining imperfections in the beans caused by deterioration occurring during the various stages of production -- growth, harvest, curing, drying, bean separating, and cleaning. Extraneous matter from the coffee berry such as husks and parchment, and foreign matter such as sticks and stones from improper cleaning may also be present. These imperfections and extraneous and foreign matter affect the quality and fitness of the coffee.

(4) Procedure: Determination of Extraneous Material in Coffee Beans

  1. Sample Preparation -- The sample submitted to the laboratory will usually be a composite prepared by the wharf examiner [(2)d.]. If the sample is received as individual subsamples, prepare a composite, taking equal weights from each subsample.
  2. Composite Sample -- Reduce the well-mixed composite to an analytical portion of ca 400 g by Jones Riffle Sampler or by quartering. Select 100 beans from this portion and weigh to 0.1 g. Use this weight to determine the 500-bean increments to be examined by the sequential sampling plan. Follow sequential plan [(4)c.], examining beans either visually [(4)d.] or by X-ray [(4)e.].
  3. Sequential Sampling Plan (3000 Beans)
    No. of Beans Examined No. Reject Beans Required to:
    Stop Analysis Continue Analysis Stop Analysis
    500 37 or less 38-115 116 or more
    1000 85 or less 86-115 116 or more
    1500 135 or less 135-165 166 or more
    2000 185 or less 186-215 216 or more
    2500 234 or less 235-264 265 or more
    3000 Report Results
  4. Visual Examination -- Using the sequential sampling plan, examine beans for insect damage (tunnels) and mold with the naked eye or about 5X magnification. Use higher magnification, as necessary, to confirm questionable areas. Classify and count the beans that are insect infested. For the purpose of this examination, classify as rejects only clearly identifiable insect damage and beans with bored holes or tunnels diagnostic of insect damage. If useful, identify the type of insect damage [(3)a.(i) or (ii).]. Minor damage by insects may be indistinguishable from mechanical damage or minor breakage. Classify, count, and report rejects as insect-damaged [(4)f.]. Classify, count and report rejects as moldy when those beans show mold growth on 1/4 or more of the surface. Describe the general appearance of the moldy areas as "white surface mold," "green staining mold," "fruiting bodies," etc., in the "Remarks" section of the report.
  5. X-Ray Examination -- Weigh equivalent of 3,000 beans in 500-bean increments. Place on X-ray sample holders, marking 500-bean increments. Expose as in Chapter IV, X-Ray Methods. Develop, dry, and examine films sequentially for insect-damaged beans. Examine the same increments visually for moldy beans [(3)b).].
  6. Report -- Tabulate results as follows:
      Subsample No.
    1 2 3 etc.
    Total Number Beans Examined        
    Total Rejects
    a Describe types of insect damage under "Remarks" (optional)
    b Describe appearance of mold under "Remarks"

(5) Procedure: Determination of Insect-Damaged and Moldy Coffee Beans

Weigh sample or subsamples as submitted and report weight in grams. Examine macroscopically for rodent excreta, manure, insects, mold, presence of sweeps, or other evidence of contamination.

Record kind and size of excreta, including number of rodent pellets or pieces, and total weight of each kind; number of each type of insect; number, size, and total weight, each, of sticks, stones, dirt clumps, paper, straw, etc. Note presence of any live insects.

(6) Procedure: Quality Grading of Coffee Beans

Grading of green coffee beans is performed according to a prescribed procedure which lists twelve types of defects that may be present. Defects include beans with various types of imperfections, sticks, stones, dirt clumps, pods, or other extraneous matter. Defects are separated macroscopically and scored to determine the grade. A sample scoring Grade 8 or worse is considered unfit. The grading procedure is described in Appendix I, page V-5-10.


  1. "Health and Safety in the Importation of Green Coffee into the United States," prepared by National Coffee Association of U.S.A., Inc., in cooperation with U.S. FDA, Undated.
  2. Lepper, Henry A., "The Grading of Coffee." Food Control Statement No. 26, March 16, 1931 (Reprinted in part in Appendix 1), FDA By-Lines, Vol. 7, No. 6, May 1977, pp. 285-291.
  3. Sivetz, M., and N.W. Desrosier, Coffee Technology, AVI Publishing Co., Westport, CT, 1979.

Appendix I
The Grading Of Coffee*

By Henry A. Lepper

(Editor's Note: This article is being reprinted in part from Food Control Statement No. 26, March 16, 1931. The principles of coffee grading have not changed in recent years, and FDA may make detentions of import coffee on the basis of the criteria described here. The original article was prepared by H.A. Lepper (deceased) of the Division of Food, who for many years was FDA's expert on grading coffee.)

Unofficial grading of coffee is done by the trade on well-established principles, the result of years of experience. The recognized imperfections are "blacks," "part blacks," "browns," "quakers," "sailors," "shells," pods, husks, "parchment," broken berries, sticks, and stones. There is not a unanimity of opinion that all of these should be regarded as imperfections. Each "black" is counted as one imperfection. The other inhibited berries and material are scored in terms of equivalency to one "black." The relationships of the "blacks" to the other imperfections are not definitely established and different members of the trade have a somewhat different, though not widely divergent, understanding of them. The number of imperfections which go to fix each grade seems to be more uniformly agreed upon. Grade 1 represents complete freedom from imperfections. Such coffee is not an article of commerce. The several grades, as determined by the number of imperfections present, are given in Table 1. Each grade is separated from the other by 50 points and the number of imperfections for intermediate grades at five point intervals also given. The size of the sample on which the count of imperfections is made is not of uniform practice in the trade. This will be referred to later. In trade or in official exchange gradings the imperfections are counted up to grade 7. From grades 7 to 8 and lower, grading is done by visual comparison with standard exchange type grade samples, the intermediate points being estimated.

Description of Kinds of Coffee Berries and Foreign Material 

Sound Coffee
The berries are generally smooth, of waxy appearance, ranging from light yellow to dark green in color.

These, as the name indicates, are black in color. They are of two classes:
(1) Those of smooth, waxy appearance, not unlike sound coffee but black in color
(2) Those shriveled and black

Part Blacks
These are sound in part and have black areas ranging from small spots to almost the entire berry.

These resemble the blacks, there being both waxy and shriveled types. They are decidedly brown in color.

* Lepper, H.A. FDA By-Lines, Vol. 7, No. 6, May 1977. pp 285-291.

TABLE 1: Number of "Blacks" (Imperfections) for Grades of Coffee From 1 to 9 With Intermediate Grades of Five Points Each
Grade "Blacks" Grade "Blacks" Grade "Blacks" Grade "Blacks"
1   None 3   13 5   58 7   200
1-05 2+45 3/5 3-05 4+45 14 7/10 5-05 6+45 64 7-05 8+45 225
1-10 2+40 1 1/5 3-10 4+40 16 2/5 5-10 6+40 70 7-10 8+40 250
1-15 2+35 1 4/5 3-15 4+35 18 1/10 5-15 6+35 76 7-15 8+35 275
1-20 2+30 2 2/5 3-20 4+30 19 4/5 5-20 6+30 81 7-20 8+30 300
1-25 2+25 3 3-25 4+25 21 1/2 5-25 6+25 87 7-25 8+25 325
2+20 1-30 3 3/5 4+20 3-30 23 1/5 6+20 5-30 92 8+20 7-30 350
2+15 1-35 4 1/5 4+15 3-25 24 9/10 6+15 5-35 98 8+15 7-35 375
2+10 1-40 4 4/5 4+10 3-40 26 3/5 6+10 5-40 103 8+10 7-40 400
2+05 1-45 5 2/5 4+05 3-45 28 3/10 6+05 5-45 109 8+05 7-45 425
2   6 4   30 6   115 8   450
2-05 3+45 6 7/10 4-05 5+45 32 4/5 6-05 7+45 123 8-05 9+45 490
2-10 3+40 7 2/5 4-10 5+40 35 3/5 6-10 7+40 132 8-10 9+40 530
2-15 3+35 8 1/10 4-15 5+35 38 2/5 6-15 7+35 140 8-15 9+35 570
2-20 3+30 8 4/5 4-20 5+30 41 1/5 6-20 7+30 149 8-20 9+30 610
2-25 3+25 9 1/2 4-25 5+25 44 6-25 7+25 157 8-25 9+25 650
3+20 2-30 10 1/5 5+20 4-30 46 4/5 7+20 6-30 166 9+20 8-30 690
3+15 2-35 10 9/10 5+15 4-35 49 3/5 7+15 6-35 174 9+15 8-35 730
3+10 2-40 11 3/5 5+10 4-40 52 2/5 7+10 6-40 183 9+10 8-40 770
3+05 2-45 12 3/10 5+05 4-45 55 1/5 7+05 6-45 191 9+05 8-45 810

"Blights" is a name also applied to these shriveled berries, ranging in color from light yellow or green to very light brown. Some of the darker colored are difficult to distinguish from shriveled "browns," but this need cause no confusion, as their relative weight in grading is the same.

As the name intimates, these berries float. They are white or nearly white, not having the waxiness of normal coffee, appearing as though deficient in fat.

The name, in this case, is descriptive, as these berries resemble the conch shell. Their usual appearance is that of sound coffee.

These are pieces of broken berries, both sound and unsound.

These are the whole coffee fruit (the "cherry"), consisting of pulp, parchment layer, silver skin, with the seeds (or berries) inside, all of which have been dried together. They are deep, dark red to almost black in color.

These are pieces of the dried pulp which have become separated from pods.

The name, in this case, classifies the material. It consists of the light yellow, thin, translucent, horny pieces, resembling parchment. They come from the layer enclosing the seeds in the fruit, when dried pods become broken in the coffee.

These are small pieces of twigs or of charcoal.

Pieces of hard earth or rock, of varying colors and sizes, are classed as stones.

It is a difficult task to separate the various imperfections from a sample of coffee on the sole basis of a verbal description, but with actual separations of known classification as examples, the grading of coffee should be much simplified.

Grading Under the Food and Drugs Act

As has previously been stated, no definite or exact knowledge is available on the composition of exchange grade 8. In applying Food Inspection Decision 108 to coffee imports, it does not appear to be necessary that this guide to quality be strictly followed. It is desirable, in view of the fact that the grade has been announced as a guide, that grading be done in such manner that only coffees of lower than grade 8 be the subject of rejected entry. It is of importance that the grading done in the various port laboratories be uniform, so that action on coffee will be the same at each port. The results of analysis and cup tests on the various imperfections show that "blacks," "browns," and "quakers" can be regarded as definitely objectionable when offered as coffee. This conclusion is backed by trade opinion. "Part Blacks" are also considered objectionable by the trade. While analysis does not indicate that much objection is to be taken to "sailors," cup tests show this separation to be of little coffee value. The trade, however, does not raise objection to this type of berry, inasmuch as it has only the effect of thinning the brew, without adding anything of detrimental character. It is reasonable, therefore, to limit the amounts of the various imperfections, with the possible exception of the "sailors," which should be present in a lot of coffee. Foreign material, such as pods, husks, sticks and stones, is naturally not coffee and should also be restricted. If the limiting values set by a system of grading devised for import work are such that coffee rejected will be below grade 8 of the trade, all requirements will apparently be met. Such grading will operate to shut out all coffees which can be regarded as trash. It will have the support of the coffee trade. Coffees below exchange grade 8 are not deliverable on exchange.

Determination of the Grade

A composite sample is taken by trier from a representative number of bags in a lot. In the routine inspection of coffee shipments the examiner can familiarize himself with the general appearance of a grade 8 type and decide, in many instances, from visual examination whether a sampling for grading by count is necessary.

From 100 grams of the well-mixed sample, the various imperfections and the sound berries are separated into groups. "Shells," "sailors," and sound, broken berries are regarded as unobjectionable. Separation can be readily accomplished after the grader has familiarized himself with the type separations. If there appears to be doubt regarding a given berry, and close comparison with the types fails to classify it, it should be regarded as sound. Often the true character of the doubtful berry can be ascertained by cutting transversely through the berry with a sharp knife. The soundness of the berry is readily judged from the internal appearance. Sometimes berries are encountered which appear to show discoloration (usually brown), but close examination shows the abnormal appearance to be confined to an adhering thin membrane, an unremoved "silver skin." On scraping with a knife, the berry beneath the skin is found to be sound. Care must be exercised not to classify such berries as unsound. Experience soon permits the grader to readily recognize these berries, as they almost always show their true character at some point by a break in the "silver skin." The "silver skin" is removed in the preparation of the coffee for the market, so that such misleading berries will be exceptional.

Occasionally a berry is found which is discolored by reason of visible mold growth. When present in numbers as a result of water damage, the coffee is adulterated and no grading is attempted. The occasional moldy berry is regarded as an imperfection. Berries showing evidence of insect infestation are not classified in grading. Coffees containing numbers of such berries are regarded as adulterated.

Broken pieces of discolored berries ("blacks," "browns") are pieced together to approximately form whole berries and each of such reconstructed berries is counted as one "black" or "brown," as the case may be. Pieces of husk and parchment are counted together. The pieces are grouped in units approximately equal to that found on a pod. Each unit is then counted as one pod. Berries which are partially discolored (with the exception of black discoloration) or which are shriveled at one end, less than one-half berry, are exceptional and usually disregarded. In those rare instances where a sample consists, in large part, of this kind of berry it needs special consideration, as it is not easily graded. Samples of this kind are seldom encountered. One sample has come to our attention consisting of many berries which were brown and shriveled at one end and this was identified by a number of the trade as a frosted coffee.

After the imperfections are grouped, the number of each is counted and the counts evaluated in terms of "blacks" from the table of equivalents. This table agrees substantially with trade understanding.

The total number of imperfections in the 100 grams, in terms of "blacks," is multiplied by the arbitrary factor 3.7. The result is located in Table 1 and the corresponding grade is the grade of the sample.

Table of Equivalents
"Blacks" (waxy or shriveled) 1 equals 1 "black"
"Part Blacks" (one-half or more black) 1 equals 1 "black"
"Part Blacks" (less than one-half black) 2 equal 1 "black"
"Moldy" 2 equal 1 "black"
"Brown" (waxy or shriveled) 5 equal 1 "black"
"Quakers" 5 equal 1 "black"
Pods 1 equals 1 "black"
Husks and "Parchment" (equivalent to a pod) 1 equals 1 "black"
Sticks (approximately the length of a coffee berry) 1 equals 1 "black"
Sticks (pieces of charcoal the size of coffee berry) 1 equals 1 "black"
Stones (size of coffee berry) 1 equals 2 "blacks"
Sticks and stones larger or smaller in size are evaluated proportionately.

Discussion of the Factor

It has already been pointed out that there is no definitely established weight of sample on which the count of imperfection in terms of "blacks" is made, to determine the grade by Table 1. Some members of the trade refer to it as being 1 pound, and others as a "pan." A "pan" is found to hold about 13 ounces. With the table of equivalents as used herein, the count of the imperfections in terms of "blacks" in a whole can of the sample gives an average result of 450, the figure in Table 1 for grade 8. The factor 3.7 which converts 100 grams to 13 ounces is, therefore, appropriate.

Example of Grading Results
Type of Imperfection No. Equivalent Blacks
"Blacks" 58 58
"Part Blacks" 8 4
"Browns" 140 28
"Quakers" 26 5
Pods 2 2
Husks and "Parchment" 4 4
Sticks 4 5
Stones 3 5
  Total imperfections 111
  Total x 3.7 411
  Grade 8+10

An 8+10 grade is 10/50 better than an 8. It is the same as a 7-40.

This grading procedure has been used for a number of years and has not resulted in the detention of coffees which would be graded by the trade as better than 8. Applied to five samples of exchange type 8, three as of March 1930, and two as of February 1929, grades of 8 - 20, 8 - 05, 8 + 5, 8 - 10, and 8 + 10, respectively, were found. In recognition of the fact that this method of grading does not grade a sample in exact keeping with the manner in which exchange grades are established, action is not recommended on samples grading better than 8 - 20.

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