Aug., 1917
T H E J O I ' R - l T A L O F I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRI'
VINEGAR INVESTIGATION A STUDY OF THE CHANGES THAT CIDER UNDERGOES DURING FERMENTATION AND PROLONGED STORAGE AND ITS SUBSEQUENT CONVERSION INTO VINEGAR IN ROTATING GENERATORS By B. G. HARTMASA K D I,. hI. TOLNAN Received M a y 7, 1917 INTRODUCTION
I n the fall of 1913, t h e Bureau of Chemistry started a n investigation of cider vinegar made b y t h e use of a certain t y p e of rotating generator. Analyses of cider vinegars made by this process shorn a decidedly low content of non-sugar solids and it was mainly for t h e purpose of determining t h e reason for this t h a t t h e investigation was made. T h e work was conducted a t Aledina. N. Y., and extended over a period of two years. During this time t h e process was under t h e personal supervision of one of t h e authors a n d no opportunity was neglected t o make t h e investigation, in its various stages, entirely authentic. I n t h e course of t h e work about 70 samples were collected a n d analyzed. I n order t h a t no question could be raised as t o t h e authenticity of t h e samples, t h e various containers (fermenters, clearing tanks, generators, etc.) were washed with a part of t h e material in t h e nature of a test run, in identically t h e same manner as in t h e investigation proper. The various products of this test run were analyzed a n d found t o agree very well in chemical composition with t h e corresponding products of the investigation proper. T h e fruit used represented a good quality of t h e usual run of western Kew York apples for vinegar making, Baldwins a n d Greenings predominating. T h e starting materials comprised two lots of 2 0 , 0 0 0 gallons each of first pressing a n d one lot of 2 , j 0 0 gallons of second pressing juice. These lots were obtained from practically t h e same stock so t h a t little difference in their chemical composition was expected. PROCESS
The fruit was grated a n d t h e finely ground pulp subjected t o hydraulic pressure in t h e customary manner. T h e juice running from t h e presses had a temperature of about 50' F. and had a pleasant, clean taste. The yield was about 1 7 0 gallons per t o n of apples. The solids a t the various pressures did not vary much; if anything, there was a slight decrease in t h e solids as t h e pressure increased, b u t this was not consistent. The juice was pumped into fermenters of 2 0 , 0 0 0 gallons capacity a n d allowed t o ferment spontaneously. The pomace remaining after t h e juice h a d been removed was firm and dry. This pomace was stored in heaps for about three days a n d t h e n repressed without t h e addition of water under t h e same conditions as t h e first pressings. During t h e storing period t h e pomace showed signs of fermentation, evidenced by a rise in temperature in t h e center of t h e heap. The second pressing juice, which amounted t o about one-ninth of t h e total available juice of t h e apple, was fermented spontaneously. Both t h e first a n d second pressing juices after completing fermentation were aged for about one year in t h e original fer-
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menters. After this time, t h e fermented first a n d second pressings were mixed in a ratio of about g : I , respectively; i. e . , 8947 gallons of each of t h e first pressings, and 2,105 gallons of t h e second pressings. This mixture constituted t h e cider vinegar stock, being t h e starting material for t h e subsequent operations. T h e stock was aged for one month, a n d was divided into two parts. One part was cleared on beechwood shavings and t h e other part was filtered through paper pulp. T h e time occupied for clearing was about twelve days. The cleared and filtered stocks were then pumped into t h e generators, ten generators for each portion. The generators were of t h e * rotating type. They consisted of a rectangular t a n k of about 480 gallons capacity, for holding t h e stock, and a cylindrical d r u m filled with beechwood shavings. The d r u m dipped into t h e cider t o t h e depth of about one-third of its diameter, and revolved very slowly through t h e stock in t h e t a n k , about I I / * turns in 24 hours. The heat of acetification caused sufficient circulation of air t o furnish the oxygen required for t h e life of t h e acetic bacteria I n this mode of generating it is not necessary to prepare a feed, t h e stock being generated without t h e addition of vinegar. I n Table I t h e average temperature of t h e generator room, t h e temperature in t h e generators, and t h e acidity for t h e cleared stock are given. Practically the same conditions prevaikd for t h e filtered stock: TABLEI-GENERATOR RECORD OF T H E End of 1st TEMPERATURE: Generator R o o m . , , . . . 58: In Generators , . . . . , , , 75 ACIDITY AS ACETIC: g. per 100 cc., , , . . , 3 . 0
. . .
CLEARED STOCK 2nd 3rd 4th week 60' 54' 55' F. 68' 62'F. 84' 5 .O 6.1 6.5
The time required for generating t h e cleared and filtered stocks was about 2 7 days. The vinegars were then pumped into tanks filled with beechwood shavings where they were allowed t o clear for about one month, when they were drawn off into storing tanks. After storing for about seven months, t h e vinegars were finally cleared on beechwood shavings. From this description, it is evident t h a t , for t h e manufacture of vinegars by t h e practice described, the time required is about two years. Practically t h e entire process is conducted in closed vessels whereby evaporation is reduced t o a minimum. The loss through shrinkage for the two first pressing juices during fermentation and storage was about 3 . j per cent on t h e average. An a t t e m p t was made t o determine t h e shrinkage during t h e other stages of manufacture, but no satisfactory results were obtained. The pomace remaining after t h e second pressing juice was removed showed a sugar content of 2 . 4 per cent a n d an acidity (as malic) of 0.85 per cent. The sediments remaining after t h e fermented ciders had been stored one year had a yellow color a n d contained dead yeast cells, bacteria, and small amounts of molds a n d starch. I n Table I1 analyses of t h e sediments of t h e two juices are given: Gals. Lot 1 . . 403 Lot 2 . . . . . . 345 AVERAGE...374
. ...
TABLEI1 COMPOSITION OF SEDIMENTS: GRAMSPER 100 Cc. Solids Ash Total P ~ O J Soluble PzOr Insoluble P*Os 0.159 0.032 14.6 0.52 0.191 15.0 0.57 0.223 0.173 0.050 14.8 0.55 0.21 0.17 0.04
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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Vol. 9, No. 8
Bureau. This is especially true of ‘the sucrose content and, in a less degree, of the non-sugar solids and fixed acids. The discrepancies are explained by the fact t h a t the Bureau samples were sterilized for one hour a t 180 t o 190’ F. and analyzed about four months after t h e Medina samples were analyzed. Analyses TABLE 111-COMPOSITIONOF VINEGARS FROM THE INDIVIDUAL GENERATORS made a t Medina a n d t h e Bureau of second pressings -- CLEAREDSTOCK-FILTERED STOCKACIDas ACID as show t h e same discrepancies as noted above and are SOLIDS ALCOHOLASH acetic SOLIDSALCOHOLASH acetic G. per % b y G. per G. per G. per % by G. per G. per due t o the same causes. 100 cc. volume 100 cc. 100 cc. 100 cc. volume 100 cc. 100 cc. Table I V shows quite a difference in solids, non1.19 0.08 0.32 6.48 1.21 0.18 0.32 6.60 1.26 0.08 0.31 6.45 1.36 0.08 0.31 6.60 sugar solids and fixed acids between t h e vinegar stock 1.44 o.20 0.32 1.21 0.28 0.32 6.60 proper a n d t h e theoretical composition of the vinegar 1.23 0.30 0.31 6.69 2:6.48 ; 1.32 o.26 0*32 6.69 1.37 0.33 0.31 6.42 stock. This difference is due t o changes during stand1.22 0.63 0.32 6.30 1.38 0.35 0.31 6.45 ing before analysis was made. 1.22 0.41 0.32 6.60 1.49 0.03 0.34 6.39 1.28 0.19 0.32 6.69 1.43 .... 0.32 6.72 FIRST PRESSING JUIcEs-There is no material differ1.27 0.04 0.32 6.69 1.38 0.08 0.33 6.57 - - - - - - - ence in chemical composition between t h e two juices. Av., 1.24 0.25 0.32 6.57 1.39 0.17 0.32 6.54 (See Table IV.) I n order t o obtain an idea of t h e composition of SECOND PRESSING JmcE-Table V shows the differt h e vinegars from t h e individual generators, a sample ence in composition between t h e first and second was t a k e n from t h e spigot of each generator just be- pressing juices: fore drawing off into t h e run-off tanks. TABLE V-COMPOSITION O F 1ST AND 2ND PRESSINGS PRFSSING: ................................ 1st 2nd T h e average composition of t h e vinegars from t h e Alcohol, per cent by volume.. ....................... 0.07 2.25 individual generators agrees fairly well with t h a t of Solids, grams per 100 cc.. ........................... 14.98 8.74 5.45 Sugars as invert sugar before inversion, grams per 100 cc. 11.92 t h e composite vinegars from t h e run-off tanks. How- Sucrose, grams per 100 cc.. .......................... 0.24 0.10 Non-sugar solids, grams per 100 cc.. ................. 2.82 3.19 ever, there is some variation among t h e vinegars from Ash, grams per 100 cc.. ............................. 0.33 0.37 27.4 32.7 Total PzOa, mg. per 100 cc. ......................... t h e generators of t h e same set. Fixed acid as malic, grams per 100 cc.. ............... 0.57 0.74 Volatile acid as acetic, grams per 100 cc.. ............. 0.02 0.26 From Table I V i t will be seen t h a t there is quite a It is reasonable t o assume t h a t t h e juice still remaindifference in chemical composition between t h e “1st Pressing Juices” analyzed a t Medina and a t t h e ing in t h e fresh pomace, after t h e removal of t h e first Since t h e material from which t h e sediments were obtained was approximately 2 0 , o o o gallons in each case, it appears from Table I1 t h a t about 4 mg. of phosphoric acid as PzO6 a n d I O mg. of ash per IOO cc. juice were removed during fermentation a n d storing.
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RAMS PER 100 Cc. EXCEPT WHERE OTHERWISE NOTED RESULTS I N G: VINEGARS AND INTERMEDIARY PRODUCTS: TABLE IV-COMPOSITION OF JUICBS, FINISHED SUGARS as Invert Sugar
k
-
M
.s9 1.. 2
B
e:
S ~ zsg:
s m
dgtl
M
@ S $I$ 58 $2 JUICE, lsT PRESSING: from Press.. from Press... composite, analyzed Medina.. composite, analyzed Bureau. fermented. fermented, stored.. from Press.. from Press.. composite, analyzed Medina.. composite, analyzed Bureau.. fermented.. fermented, stored.. JUICE. ZND PRESSING: from Press.. composite, analyzed Medina.. composite, analyzed Bureau. fermented fermented, stored.. Vinegar Stock: 1st and 2nd Pressings, mixed.. Vinegar Stock: cleared. filtered. V inegar : cleared stock.. filtered stock.. Cleared Vinegar: cleared stock.. filtered stock.. Vinegar, stored: filtered stock. cleared stock.. SUMMARY JUICE, analyzed Bureau: composite, . 1st Pressing. composite, 2nd Pressing JUICE, fermented, stored: 1st Pressing 2nd Pressing.. Vinegar stock: theoretical prop? Vinegar, filtered s t o u Cleared Vinegar. Vinegar, stored: filtered stock (*) Determjned in distillate. (t) Determined by difference.
................... ..................
.... ..........................
............. ................... ................... .... .... .................... ............. 1.0341 2.10 ................... 10/27/13 1.0325 2.54 .... 10/27/13 10/27/13 1.0334 2.25 ..... 12/ 3/13 1.0058 5.25 ...................... 1.0053 5.45 ............. 11;/23;/14 0.99849 7.00 5/15 0.99850 7.01 ................... 12/1/ 7/14 5.75 ........................ l > ’ J ) l S 0.’99860 7.01 ....................... 1/31/15 1.0156 0.20 .................. 1/30/15 1.0150 0.18 ................... 3/ 1/15 1.0152 0.20 ................. ................. 3/ 1/15 1.0159 0.17 10/ 2/15 1.0159 0.04 ................... 4/15 1.0155 0.06 ................. 10/ 1.0592 0.07 ................... 10/27/13 1.0334 2.25 ......... 10/24/13 11/23/14 0.99820 7.40 .................... ................. 5.45 . . . . . . . .11/23/14 . . . . . . 1.0053 . . . . 7.20 ............. 12/ 7/14 0.99849 7.00 ............. 3/1/30/15 1.0150 0.18 ................. 1/15 1.0159 0.17 ...... 10/. 3/15 . 1.0159 0.04
Z
P
.... 2.05 3.23 .... .... 1.81 3.52 .... .... 2.30 3.14 .... .... 0.24 .... .......... 0.06 .... 2.82 1.72 .... .......... 0.03 .... 1.55 None 9.01 12.38 .... 3.20 2.46 .... 8.90 12.08 .... 3.02 2.75 .... 8.61 11.62 .... 2.86 ........ 11.53 12.14 .... 0.58 2.72 .... .......... .... 1.61 .... .......... 0.05 0.03 .... 1.51 None 8.86 5.17 5.28 .... 0.10 3.59 .... 8.85 5.28 5.44 .... 0.15 3.42 .... 8.74 5.45 5.56 .... 0.10 3.19 .... 2.72 0.20 ..... 0.22 0.00 2.52 .... 2.13 .......... 0.09 .... 2.04 None 1.51 .......... 0.03 .... 1.48 None 1.51 .......... 0.03 .... 1.48 None 1.30 .......... 0.03 .... 1.27 None 1.51 .......... 0.03 .... 1.48 None 10.35 9.90 9.39 11.92
12.51 11.81 11.81 12.17
.... 1 19 0.27(* .... 1:27 0.27(*]
0.69 0.70 0.67 0.59 0.80 0.83 0.63 0.64 0.74 0.64 0.82 0.82
.......................... .......................... .......................... .............. 0.25 0.040 ..... 0.26 0.028 0.046 .................. .......................... .......................... .............. 0.26 0.040 ..... 0.26 0.020 0.058 0.25 0.79 0.37 ...................... 0.26 0.85 0.39 ...................... 0.26 0.74 0.37 37.0 32.7 . . . . . . . . . . . . . . 1.01 0.35 0.36 35.0 31.6 0.24 0.350 .....
0.09 0.07 0.02 0.02 0.43 0.47
0.59 0.62 0.65 0.57 0.33 34.0 27.4 0.32 0.32 32.5 26.5 0.31 0.33 35.4 26.5 ........ 0.30 36.0 0.01 0.63 0.02 0.72 0.02 0.62 0.32 33.4 26.7 0.48 0.29 0.32 33.0 27.5 0.48 0.29 0.33 34.6 27.7
1.07 1.14 1.03 1.47 1.47 0.78 0.77
1.02 0.34 0.39 38.0 31.7 0.25 0.193 0.074 0.49 0.24 0.33 35.0 25.8 0.25 0.041 0.044 0.47 0.25 0.33 34.6 26.0 0.25 0.046 0.044
1.31 0.77
1.02 0.18 0.30 31.6 21.4 0.24 0.048 0.023 0.48 0.24 0.33 34.6 26.0 0.25 0.046 0.044
1.26 1.34
.......... ..........
1.30 1.43
.......... 0.06 .... .......... 0.08 ....
1.24 0.30(*) 6.52(t) 6.45 0.08 0.33 33.6 23.3 0.24 0.071 0.035 1.35 0.28(*) 6.47(t) 6.41 0.07 0.32 33.2 23.6 0.25 0.076 0.035
..... 0.12 .... ..... 0.11 ....
1.20 0.33(b) 6.47(t) 6.44 0.03 0.30 34.4 23.7 0.24 0.083 0.033 1.09 0.34(b) 6.63(t) 6.58 0.06 0.31 34.6 22.1 0.25 0.076 0.033
1.32 0.45 1.20 0.45
0.07 0.07
.... 0.24 2.82 .... .... 0.103.19 .... 1.58 .......... 0.03 .... 1.55 None 2.13 .......... 0.09 .... 2.04 None 1.62 .......... 0.04 .... 1.58 None 1.51 .......... 0.03 .... 1.48 None 1.34 ......... .‘0.07 .... 1.27 0.27 1.43 .......... 0.08 .... 1.35 0.28 1.32 0.45 ..... 0.12 .... 1.20 0.33
14.98 11.92 12.17 8.74 5.45 5.56
6.52(t) 6.45 0.08 0.33 32.6 22.8 0.24 0.073 0.035 6.45(t) 6.37 0.07 0.32 31.6 22.0 0.25 0.073 0.035
0.59 1.03
0.02 0.57 0.33 34.0 27.4 0.26 0.74 0.37 37.0 32.7
0.83 0.47 1.02 1.47 0.53 0.89 0.49 0.78 6.45(*) 6.37 6.47(*) 6.41 6.47(*) . . 6.44 (a) On all ‘uices and stocks determined indirectly, in ( b ) Cc. N i l 0 acid per 100 cc.
.............. ..............
0.31 0.33 35.4 26.5 0.26 0.028 0.046 0.34 0.39 38.0 31.7 0.25 0.193 0.074 0.31 0.34 35.3 27.6 0.25 0.041 0.036 0.24 0.33 35.0 25.8 0.25 0.041 0.044 0.07 0.32 31.6 22.0 0.25 0.073 0.035 0.07 0.32 33.2 23.6 0.25 0.076 0.035 0.03 0.30 34.4 23.7 0.24 0.083 0.033 all vinegars determined directly.
Aug.5 1917
T H E J O U R N A L O F I N D U S T R I A L A N D E N G I K E E RI N G C H E M I S T R Y
pressing, has practically t h e same composition as t h e first pressing juice proper a n d t h a t t h e increase in t h e non-volatile constituents is due t o a concentration of material through evaporation of water and alcohol during t h e storing of t h e pomace before pressing. This concentration was figured t o be about 1 5 per cent. There is a marked loss of alcohol a n d acetic acid during storing of pomace-about 23 per cent of t h e total alcohol a n d acetic acid. T h e analyses of t h e two juices a n d their fermented products are so much alike t h a t i t will suffice t o confine t h e discussion t o either. This is also t r u e of t h e two final vinegars. I n order t o afford a more intelligent presentation of t h e material t o be used, t h e d a t a essential t o t h e discussion are assembled in t h e summary of Table IV. DISCUSSION O F RESULTS
761
age in acetic acid is in part accounted for by t h e formation of esters ( 0 . 8 g. ethyl acetate = I . I g. acetic acid) so t h a t t h e real loss of acetic acid during the entire process is a trifle less t h a n 3 per cent. This calculation does not take t h e concentration during acetification into account as it was impossible to determine this shrinkage. F I X E D ACIDS-The loss of fixed acids will be discussed later. ASH-The analysis does not shorn a loss of ash during fermentation a n d storing. T h a t there is a slight loss during this period was discussed in connection with‘ Table 11. During t h e storing of t h e vinegar there is a n appreciable loss, about 6 per cent. T O T A L P205-Although there is only a slight decrease in P205 during alcoholic fermentation a n d storing (probably due t o assimilation as food during t h e growth of t h e yeast), there is a n appreciable loss of this ingredient during t h e acetification, about 1 2 per cent. PENTOSANS, or their equivalent, increase about I O O per cent during t h e acetification a n d storing of t h e vinegar. T h e increase in t h e reducing substances reported as sugars is very likely due t o these so-called pentosans.
I n t h e following discussion of t h e analytical results a n d t h e changes which t a k e place during t h e process, t h e influence which t h e second pressing juice has upon t h e composition of t h e vinegars has been disregarded. This was done for t h e sake of convenience. ALcoHoL-The fermentation was very complete. T h e small amount of copper reducing substances TABLEVI-CHEMICAL COMPOSITION OF THE FINALVINEGARS ( 0 . 0 3 g. per IOO cc.) reported as invert sugar is probaResults in grams per 100 cc. except where otherwise noted bly due t o pentosans. Theoretically t h e fermented STOCK: .................. FILTERED C.I EA R ED 1.0193 1.01531 a n d stored juice should contain 6 . 2 g. of alcohol per Specific gravity at 15.6’ C./15.6O C... Alcohol, per cent by volume.. . . . . . . . 0 . 0 3 0.05 0.05 0.06 I O O cc. Of this amount, 6 . z g. are accounted for, there Glycerin .......................... 0.23 0.24 0.24 0.25 Solids. ............................ 1.31 1.32 1.19 1.22 being no apparent loss of alcohol. Sugars as invert Sugar: * 0.45 0.45 0.45 0.45 before inversion.. . . . . . . . . . . . . . . G L Y C E R I N remains fairly constant during t h e entire 0.11 0.11 after evaporation. .............. 0 . 1 2 0.12 1.19 1.10 Non-sugar solids.. . . . . . . . . . . . . . . . . . process. 0.34 0.33 Volatile reducing substance:. ........ NON-SUGAR soLms-The total reduction of non- Polarization direct at 27 C., un- -1.00 v. -0.90 v. diluted, 200 mm. t u b e . . . . . . . . . . . . 6.62 6.64 6.46 sugar solids during t h e process (from juice t o finished Total acid as acetic.. ............... 6.47 6.44 6.58 Volatile acid as acetic.. ............. vinegar) is about 58 per cent. Of this amount about Fixed acids as malic.. . . . . . . . . . . . . . . 0 . 0 3 0.05 0.06 0.03 0.79 0.85 0.91 esters as ethvl acetate.. ..... 0 . 8 0 four-fifths occurs during fermentation a n d storing Volatile 0.083 0.076 Pentosans. ........................ 0.0004 0.0004 acid. ....................... of t h e cider a n d one-fifth during acetification a n d Formic 0.033 0.032 0.033 Proteins ( N X 6.25). .............. 0.033 medium medium Lead precipitate.. .................. storing of vinegar. Of t h e total loss, about one-third Alcohol precipitate. . . . . . . 0.21 0.20 0.19 0.20 is accounted for through t h e conversion of malic Polarization of alcohol pre 4.0 Color Brewer’s scale ‘/a in. cell.. .... 4 . 6 acid into lactic acid during fermentation, a n d oxidation Per ce‘nt color removed (fuller’s earth). 25 25 0.30 0.31 Ash. ....... .................. 0.30 0 . 3 0 of malic acid during acetification. T h e remaining Alkalinity, 10 acid per 100 cc.: 34.4 34.8 34.4 34.6 soluble ash.. .................. two-thirds may be attributed t o precipitation of pec5.8 6.0 5.6 insoluble ash.. ................. 6 . 0 21.8 22.3 23.7 Total P ~ O Smg. . per 100 cc.. ......... 2 3 . 0 tins a n d gums chiefly. 10.2 10.4 11.2 Soluble P206, mg. per 100 cc.. ....... 10.2 12.5 11.6 11.9 Insoluble P?Os, mg. per 100 cc.. ...... 12.8 VOLATILE R E D U C I N G S U B S T A X C E S d o not occur in 0.004 0.004 Sulfur trioxid ............. 0.004 0.004 0.001 . . . . . . . . . . . . . 0.001 t h e juice or in t h e fermented juice. T h e y appear for 0.156 0.162 Potassium ox t h e first time in t h e vinegar so t h a t i t may be said Sodium oxide 0.003 0.008 0.015 0.013 t h a t t h e y are t h e product of acetification. T h e vola- Calcium oxide 0.010 0.014 0.0008 0.0010 (SiOz) ... tile reducing substances increase during t h e ageing Silica 0.043 0.045 0.032 0.035 Malic acid.. ....................... 0.012 0.010 0.007 0.010 Succinic acid.. ..................... of t h e vinegar. 0.28 0.29 0.23 0.22 Lactic acid.. ...................... 0.022 0.024 0.022 V O L A T I L E A C I D AS ACETIC-Based on t h e alcohol Tannin and coloring matter.. ........ 0.024 0.035 0.043 0.043 Acetates as acetic acid.. . . . . . . . . . . . . 0.043 a n d acetic acid content of t h e vinegar stock, t h e vineTable VI presents t h e chemical compositions of gar produced should theoretically have contained 7 . 7 g. of acetic acid for I O O cc., whereas only 6 . 4 g. of actual t h e final vinegars. The organic acid constituents are acetic acid are accounted for, or, during acetification, interesting because t h e y give a n idea of t h e destructive there is a n apparent loss of 1 7 per cent acetic acid. processes which t a k e place during alcoholic fermentaDuring clarification a n d storing of t h e vinegar there tion a n d acetification. T h e decrease of fixed acids duris a loss of about I per cent acetic acid, so t h a t t h e ing fermentation a n d storing is, in t h e main, due t o total loss of acetic acid during t h e entire process amounts t h e breaking down of malic acid into lactic acid a n d to approximately 18 per cent of t h e total available carbonic acid. T h e lactic acid found in t h e final acetic acid. This is a very good yield. I n practice vinegar made from t h e filtered stock is 0 . 23 g. per Assuming t h a t this lactic acid was formed t h e loss of acetic acid during acetification is placed I O O cc. a t 23 per cent, it being figured t h a t I per cent alcohol from malic only, i t follows t h a t about 0.34 g. malic by volume will yield 0 . 8 g. of acetic acid. T h e short- acid was destroyed t o form lactic acid. Unfortunately,
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THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
t h e malic acid was not determined in t h e juice. However, from t h e alkalinity of t h e water-soluble ash a n d t h e fixed acidity of a juice, i t is possible t o calculate t h e total malic acid approximately. T o do this, it must be assumed t h a t t h e fixed acidity in a n apple juice is due principally t o malic acid. Calculated in this manner, t h e two lots of juices originally contained approximately 0 . 4 6 and 0 . 4 j g. combined, and 0 . 3 4 and 0.40 g . free malic acid, respectively, or about 0.83 g. total malic acid, average for t h e two juices. Accordingly, t h e fermented and stored cider contained approximately 0 . 4 9 g. of total malic acid. The final vinegar contained about 0 . 0 4 0 g. of total malic acid. CoNCLUsIONs
F r o m t h e figures given above i t is apparent t h a t : ( I ) During fermentation a large part of t h e malic acid of t h e apple juice is destroyed t o form lactic acid. ( 2 ) During acetification t h e remaining malic acid is almost entirely oxidized. (3) T h e fixed acid in t h e vinegar is chiefly lactic acid. Other points of interest concerning t h e organic acid constituents are t h e presence of acetates in t h e vinegar a n d indications of minute amounts of formic acid, as shown b y Fincke's method. Concerning t h e ash constituents, it is noted t h a t 7 j per cent of t h e ash consists of potassium carbonate. METHODS OF A N A L Y S I S
Wherever possible, t h e methods approved by t h e Association of Official Agricultural Chemists were employed. MALIC ACID was determined by t h e method of C. von der Heide a n d H . Steiner SUCCINIC ACID was determined by t h e method of C. von der Heide a n d H . Steiner.' LACTIC ACID was determined b y t h e method of W. Moeslinger.3 On account of t h e presence of appreciable amounts of acetates i n t h e vinegars, t h e method was modified t o remove t h e acetates. This was accomplished b y t h e addition of 2 cc. of concentrated hydrochloric acid after distilling off t h e volatile acids and evaporating t o a small bulk, adding water and again evaporating, repeating this operation three times before proceeding with t h e determination of t h e lactic acid. ACETATES-The acetates were determined in t h e residue from t h e volatile acid determination. T o t h e residue in t h e distilling flask, 5 cc. of a 20 per cent phosphoric acid solution were added a n d t h e distillation continued until 1 5 cc. of distillate required not more t h a n 3 drops of N / I O alkali for neutralization. T h e acidity of t h e distillate was determined b y titration a n d calculated as acetic acid. Recognition is due t o Mr. E. H. Berry, of t h e Chicago Laboratory, for assistance rendered i n t h e analyses of a number of t h e samples. DEPARTMENT OB AGRICULTURE BUREAUOR CHEMISTRY CHICAGO, ILLINOIS Z. Nahr. Cenussm., 17 (1909). 307. I b i d . , 17 (1909), 291. 8 I b i d . , 4 (1901), 1123, Barium Chloride Method. 1 2
VOI. 9 , NO.
a
THE ACID CONTENT OF FRUITS By W. D BIGELOW A N D P. B. DUNBAR Received April 21, 1917
HISTORICAL
The statements found in t h e literature regarding t h e characteristic acids of t h e various fruits are most diverse. This is probably due in many cases t o t h e inaccuracy of t h e methods used for their identification a n d determination, although it is quite possible t h a t variations in t h e kind of acid present may sometimes occur in t h e same variety of fruit when grown under differing conditions. T h e method which has generally been used for t h e determination of both citric and malic acids in fruit juices depends on t h e precipitation of t h e acids in t h e form of calcium or barium salts and t h e separation of these by means of their differing solubilities in water a n d alcohol. The separations obtained in this way are usually far from sharp and may readily lead t o errors. The burden of evidence in t h e literature seems t o indicate t h a t tartaric acid is not a n ingredient of fruit juices except, of course, of grape juice. W. Kaupitzl* and R. Kayser2 claim t o have found tartaric acid in raspberries. b u t their statements are contradicted by numerous author^.^-^ Kunz* reports citric acid as the acid of raspberries. Kunz and Adam5 state t h a t strawberries, raspberries, elderberries, currants, cranberries a n d peaches contain citric acid b u t no malic nor tartaric. They find t h a t citric acid is t h e predominating acid of huckleberries, gooseberries and apricots b u t s t a t e t h a t malic acid is also present. Tartaric acid was not found by t h e m in these fruits. Krzizan and Plahlg a n d KrzizanG found citric acid only in raspberries. Kayser2 reports citric as t h e principal acid of raspberries, b u t found malic and tartaric acids also. Jorgensen3 found citric as t h e predominating acid of raspberries a n d huckleberries with a small amount of malic, a n d in raspberries traces also of SUCcinic b u t no tartaric: elderberries were found t o contain only citric. Hempel a n d Friedrichlo report t h e examination of four samples of raspberry juice. The first contained much citric acid a n d a not inconsiderable amount of malic. T h e second contained about equal amounts of both acids, while t h e other two contained much malic acid with traces only of citric. Keim'l found both malic and citric acids in cherries. W. Nackenlz found citric a n d malic acids in huckleberries, Mach and Portelel3 in cranberries. According t o Stolle14 cranberries ( Vaccinium o x y c o c c u s ) contained only glyoxylic acid, while Aparin15 reports only citric acid. From t h e work of t h e authors just quoted, Windisch a n d Schmidt,16 from whose paper these references are taken, draw t h e following conclusions: Citric a n d malic acids are t h e characteristic acids of fresh fruit juices, excluding grape juice. Succinic acid is found in small quantities in fresh fruit, especially in t h e unripe condition, b u t tartaric acid does not occur in other fruits t h a n grapes. I n berries, in general, citric acid predominates a n d most berries contain, i n addition, malic acid in very small quantities. Of t h e
* Numbers refer t o bibliography on page 767.
