All About Coffee Part 34

Shake vigorously 100 grams or more of the sample with cold water or 70 percent alcohol by volume. Strain through a coa.r.s.e sieve and allow to settle. Identify soluble colors in the solution and insoluble pigments in the sediment.

ROASTED COFFEE

3. _Macroscopic Examination--Tentative_

Artificial coffee beans are apparent from their exact regularity of form. Roasted legumes and lumps of chicory, when present in whole roasted coffee, can be picked out and identified microscopically. In the case of ground coffee, sprinkle some of the sample on cold water and stir lightly. Fragments of pure coffee, if not over-roasted, will float; while fragments of chicory, legumes, cereals, etc., will sink immediately, chicory coloring the water a decided brown. In all cases identify the particles that sink by microscopical examination.

4. _Preparation of Sample--Official_

Grind the sample to pa.s.s through a sieve having holes 0.5 mm. in diameter and preserve in a tightly stoppered bottle.

5. _Moisture--Tentative_

Dry 5 grams of the sample at 105--110C. for 5 hours and subsequent periods of an hour each until constant weight is obtained. The same procedure may be used, drying _in vacuo_ at the temperature of boiling water. In the case of whole coffee, grind rapidly to a coa.r.s.e powder and weigh at once portions for the determination without sifting and without unnecessary exposure to the air.

6. _Soluble Solids--Tentative_

Place 4 grams of the sample in a 200-cc. flask, add water to the mark, and allow the ma.s.s to infuse for eight hours, with occasional shaking; let stand 16 hours longer without shaking, filter, evaporate 50 cc. of filtrate to dryness in a flat-bottomed dish, dry at 100 C., cool and weigh.

7. _Ash--Official_

Char a quant.i.ty of the substance, representing about 2 grams of the dry material, and burn until free of carbon at a low heat, not to exceed dull redness. If a carbon-free ash can not be obtained in this manner, exhaust the charred ma.s.s with hot water, collect the insoluble residue on a filter, burn till the ash is white or nearly so, and then add the filtrate to the ash and evaporate to dryness. Heat to low redness, until ash is white or grayish white, and weigh.

8. _Ash Insoluble in Acid--Official_

Boil the water-insoluble residue, obtained as directed under 9, or the total ash obtained as directed under 7, with 25 cc. of 10-percent hydrochloric acid (sp. gr. 1.050) for 5 minutes, collect the insoluble matter on a Gooch crucible or an ashless filter, wash with hot water, ignite and weigh.

9. _Soluble and Insoluble Ash--Official_

Heat 5 to 10 grams of the sample in a platinum dish of from 50 to 100 cc. capacity at 100 C. until the water is expelled, and add a few drops of pure olive oil and heat slowly over a flame until swelling ceases.

Then place the dish in a m.u.f.fle and heat at low redness until a white ash is obtained. Add water to the ash, in the platinum dish, heat nearly to boiling, filter through ash-free filter paper, and wash with hot water until the combined filtrate and washings measure to about 60 cc.

Return the filter and contents to the platinum dish, carefully ignite, cool and weigh. Compute percentages of water-insoluble ash and water-soluble ash.

10. _Alkalinity of the Soluble Ash--Official_

Cool the filtrate from 9 and t.i.trate with N/10 hydrochloric acid, using methyl orange as an indicator.

Express the alkalinity in terms of the number of cc. of N/10 acid per 1 gram of the sample.

11. _Soluble Phosphoric Acid in the Ash--Official_

Acidify the solution of soluble ash, obtained in 9, with dilute nitric acid and determine phosphoric acid (P_2_O_5). For percentages up to 5 use an aliquot corresponding to 0.4 gram of substance, for percentages between 5 and 20 use an aliquot corresponding to 0.2 gram of substance, and for percentages above 20 use an aliquot corresponding to 0.1 gram of substance. Dilute to 75-100 cc., heat in a water-bath to 60-65 C., and for percentages below 5 add 20-25 cc. of freshly filtered molybdate solution. For percentages between 5 and 20 add 30-35 cc. of molybdate solution. For percentages greater than 20 add sufficient molybdate solution to insure complete precipitation. Stir, let stand in the bath for about 15 minutes, filter _at once_, wash once or twice with water by decantation, using 25-30 cc. each time, agitate the precipitate thoroughly and allow to settle; transfer to the filter and wash with cold water until the filtrate from two fillings of the filter yields a pink color upon the addition of phenolphthalein and one drop of the standard alkali. Transfer the precipitate and filter to the beaker, or precipitating vessel, dissolve the precipitate in a small excess of the standard alkali, add a few drops of phenolphthalein solution, and t.i.trate with the standard acid.

12. _Insoluble Phosphoric Acid in the Ash--Official_

Determine phosphoric acid (P_2_O_5) in the Insoluble ash by the foregoing method.

13. _Chlorides--Official_

Moisten 5 grams of the substance in a platinum dish with 20 cc. of a 5-percent solution of sodium carbonate, evaporate to dryness and ignite as thoroughly as possible at a temperature not exceeding dull redness.

Extract with hot water, filter and wash. Return the residue to the platinum dish and ignite to an ash; dissolve in nitric acid, and add this solution to the water extract. Add a known volume of N/10 silver nitrate in slight excess to the combined solutions. Stir well, filter and wash the silver chloride precipitate thoroughly. To the filtrate and washings add 5 cc. of a saturated solution of ferric alum and a few cc.

of nitric acid. t.i.trate the excess silver with N/10 ammonium or pota.s.sium thiocyanate until a permanent light brown color appears.

Calculate the amount of chlorin.

14. _Caffein--The Fendler and Stuber Method--Tentative_

Pulverize the coffee to pa.s.s without residue through a sieve having circular openings 1 mm. in diameter. Treat a 10-gram sample with 10 grams of 10-percent ammonium hydroxid and 200 grams of chloroform in a gla.s.s-stoppered bottle and shake continuously by machine or hand for one-half hour. Pour the entire contents of the bottle on a 12.5-cm.

folded filter, covering with a watch gla.s.s. Weigh 150 grams of the filtrate into a 250-cc. flask and evaporate on the steam bath, removing the last chloroform with a blast of air. Digest the residue with 80 cc.

of hot water for ten minutes on a steam bath with frequent shaking, and let cool. Treat the solution with 20 cc. (for roasted coffee) or 10 cc.

(for unroasted coffee) of 1-percent pota.s.sium permanganate and let stand for 15 minutes at room temperature. Add 2 cc. of 3-percent hydrogen peroxid (containing 1 cc. of glacial acetic acid in 100 cc.). If the liquid is still red or reddish, add hydrogen peroxid, 1 cc. at a time, until the excess of pota.s.sium permanganate is destroyed. Place the flask on the steam bath for 15 minutes, adding hydrogen peroxid in 0.5-cc.

portions until the liquid becomes no lighter in color. Cool and filter into a separatory funnel, washing with cold water. Extract four times with 25 cc. of chloroform. Evaporate the chloroform extract from a weighed flask with aid of an air blast and dry at 100 C. to constant weight (one-half hour is usually sufficient). Weigh the residue as caffein and calculate on 7.5 grams of coffee. Test the purity of the residue by determining nitrogen and multiplying by 3.464 to obtain caffein.

15. _Caffein--Power-Chestnut Method--Official_

Moisten 10 grams of the finely powdered sample with alcohol, transfer to a Soxhlet, or similar extraction apparatus, and extract with alcohol for 8 hours. (Care should be exercised to a.s.sure complete extraction.) Transfer the extract with the aid of hot water to a porcelain dish containing 10 grams of heavy magnesium oxid in suspension in 100 cc. of water. (This reagent should meet the U.S.P. requirements.) Evaporate slowly on the steam bath with frequent stirring to a dry, powdery ma.s.s.

Rub the residue with a pestle into a paste with boiling water. Transfer with hot water to a smooth filter, cleaning the dish with a rubber-tipped gla.s.s rod. Collect the filtrate in a liter flask marked at 250 cc. and wash with boiling water until the filtrate reaches the mark.

Add 10 cc. of 10-percent sulphuric acid and boil gently for 30 minutes with a funnel in the neck of the flask. Cool and filter through a moistened double paper into a separatory funnel and wash with small portions of 0.5-percent sulphuric acid. Extract with six successive 25-cc. portions of chloroform. Wash the combined chloroform extracts in a separatory funnel with 5 cc. of 1-percent pota.s.sium hydroxid solution.

Filter the chloroform into an Erlenmeyer flask. Wash the pota.s.sium hydroxid with 2 portions of chloroform of 10 cc. each, adding them to the flask together with the chloroform washings of the filter paper.

Evaporate or distil on the steam bath to a small volume (10-15 cc.), transfer with chloroform to a tared beaker, evaporate carefully, dry for 30 minutes in a water oven, and weigh. The purity of the residue can be tested by determining nitrogen and multiplying by the factor 3.464.

16. _Crude Fiber--Official_

Prepare solutions of sulphuric acid and sodium hydroxid of exactly 1.25-percent strength, determined by t.i.tration. Extract a quant.i.ty of the substance representing about 2 grams of the dry material with ordinary ether, or use residue from the determination of the ether extract. To this residue in a 500-cc. flask add 200 cc. of boiling 1.25-percent sulphuric acid; connect the flask with a reflux condenser, the tube of which pa.s.ses only a short distance beyond the rubber stopper into the flask, or simply cover a tall conical flask, which is well suited for this determination, with a watch gla.s.s or short stemmed funnel. Boil at once and continue boiling gently for thirty minutes. A blast of air conducted into the flask may serve to reduce the frothing of the liquid. Filter through linen, and wash with boiling water until the washings are no longer acid; rinse the substance back into the flask with 200 cc. of the boiling 1.25-percent solution of sodium hydroxid free, or nearly so, of sodium carbonate; boil at once and continue boiling gently for thirty minutes in the same manner as directed above for the treatment with acid. Filter at once rapidly, wash with boiling water until the washings are neutral. The last filtration may be performed upon a Gooch crucible, a linen filter, or a tared filter paper. If a linen filter is used, rinse the crude fiber, after washing is completed, into a flat-bottomed platinum dish by means of a jet of water; evaporate to dryness on a steam bath, dry to constant weight at 110 C., weigh, incinerate completely, and weigh again. The loss in weight is considered to be crude fiber. If a tared filter paper is used, weigh in a weighing bottle. In any case, the crude fiber after drying to constant weight at 110 C., must be incinerated and the amount of the ash deducted from the original weight.

17. _Starch--Tentative_

Extract 5 grams of the finely pulverized sample on a hardened filter with five successive portions (10 cc. each) of ether, wash with small portions of 95-percent alcohol by volume until a total of 200 cc. have pa.s.sed through, place the residue in a beaker with 50 cc. of water, immerse the beaker in boiling water and stir constantly for 15 minutes or until all the starch is gelatinized; cool to 55 C., add 20 cc. of malt extract and maintain at this temperature for an hour. Heat again to boiling for a few minutes, cool to 55 C., add 20 cc. of malt extract and maintain at this temperature for an hour or until the residue treated with iodin shows no blue color upon microscopic examination.

Cool, make up directly to 250 cc., and filter. Place 200 cc. of the filtrate in a flask with 20 cc. of hydrochloric acid (sp. gr. 1.125); connect with a reflux condenser and heat in a boiling water bath for 2.5 hours. Cool, nearly neutralize with sodium hydroxid solution, and make up to 500 cc. Mix the solution well, pour through a dry filter and determine the dextrose in an aliquot. Conduct a blank determination upon the same volume of the malt extract as used upon the sample, and correct the weight of reduced copper accordingly. The weight of the dextrose obtained multiplied by 0.90 gives the weight of starch.

18. _Sugars--Tentative_

See original.[186]

19. _Petroleum Ether Extract--Official_

Dry 2 grams of coffee at 100 C., extract with petroleum ether (boiling point 35 to 50 C.) for 16 hours, evaporate the solvent, dry the residue at 100 C., cool, and weigh.

20. _Total Acidity--Tentative_

Treat 10 grams of the sample, prepared as directed under 4, with 75 cc.

of 80-percent alcohol by volume in an Erlenmeyer flask, stopper, and allow to stand 16 hours, shaking occasionally. Filter and transfer an aliquot of the filtrate (25 cc. in the case of green coffee, 10 cc. in the case of roasted coffee) to a beaker, dilute to about 100 cc. with water and t.i.trate with N/10 alkali, using phenolphthalein as an indicator. Express the result as the number of cc. of N/10 alkali required to neutralize the acidity of 100 grams of the sample.

21. _Volatile Acidity--Tentative_

Into a volatile acid apparatus introduce a few gla.s.s beads, and over these place 20 grams of the unground sample. Add 100 cc. of recently boiled water to the sample, place a sufficient quant.i.ty of recently boiled water in the outer flask and distil until the distillate is no longer acid to litmus paper. Usually 100 cc. of distillate will be collected. t.i.trate the distillate with N/10 alkali, using phenolphthalein as an indicator. Express the result as the number of cc.

of N/10 alkali required to neutralize the acidity of 100 grams of the sample.