The Chemical and Properties of Dioxide Solution for Brining Fruit

Circular of Information 629 June 1969

Agricultural Experiment Station, Oregon State University, Corvallis The Chemical and Preservative Properties of Solution for Brining Fruit

C. H. PAYNE, D. V. BEAVERS, and R. F. CAIN Department of Food Science and Technology

Sweet cherries and other fruits are preserved in sul- control are given in by Waiters et al. (1963) and fur dioxide solutions for manufacture into maraschino, Yang et al. (1966). cocktail, and glace fruit. The sulfur dioxide solution, Sulfur dioxide and are directly related to commonly called brine, may be prepared from liquid brined cherry quality. Improper use of these chemicals sulfur dioxide, , or may result in cherries that are soft, poorly bleached, or using alkali or acid to control pH. Calcium salts such as spoiled due to fermentation. It is the purpose of this , calcium carbonate, and calcium chlo- circular to show how the basic chemical and preservative ride are added to the brine to prevent cracking and pro- components of brine solutions are afifected during prep- mote firming of the fruit tissue through interaction with aration, storage, and use. pectic materials. Directions for brine preparation and

Chemical Properties of Sulfur Dioxide Solutions

When sulfur dioxide or materials containing sulfur range of sulfur dioxide concentrations, the relative dis- dioxide (bisulfite or metabisulfite) are dissolved in tribution of the sulfur dioxide ionic forms is constant. , three types of chemical substances are formed: Within the initial pH range used for brining cher- (H2SO3),1 bisulfite (HSO3"), and ries, there is a predominance of (SO~). The amount of each substance formed depends (Ca(HS03)2) and sulfurous acid (HjSOs), both upon the pH ( concentration) of the solu- forms being water soluble. However, tion, which is regulated by the amount of sulfur dioxide (CaSOs), which is highly insoluble, precipitates as the present and/or by addition of acid or alkali. The effect pH of the brine is adjusted upward, giving the brine a of pH upon the ionic forms of sulfur dioxide is shown milky-white appearance. This usually occurs within a in Figure 1. Brine solutions containing sulfur dioxide range of pH 2.8-3.2, varying with the sulfur dioxide exhibit the same general equilibrium characteristics; concentration and temperature of the sulfur dioxide so- their chemical properties are somewhat dififerent, how- lution. For example, lower sulfur dioxide concentrations ever, since brine solutions form insoluble calcium sulfite. and/or cool brine temperatures shift the precipitation The chemical reaction for sulfur dioxide-calcium brine point of calcium sulfite and permit adjustment of brine is given below. to higher pH values. Formation of white calcium su'fite precipitate indicates excessive use of alkali and should be Ca(OH), Ca(OH) 2 avoided. Cherries placed in brine solutions containing S0 + H 0^±H SO ^± Ca (HSCM^CaSOjJH-H.O 2 2 2 s calcium sulfite or solutions with an initial pH above 3.2 Addition of alkali raises the pH and shifts the reac- may be inadequately bleached and are subject to crack- tion to the right, while lowering the pH with acid forces ing and spoilage. Brines prepared with insufficient alkali a shift to the left. An increase or decrease in tempera- (pH below 2.5) lose excessive amounts of sulfur dioxide ture will bring about a left or right shift respectively. to the atmosphere during brining and this may cause For any given pH and temperature within a limited cracking and softening of the fruit. The alkali/acid ad- justment of brines should be such that the sulfurous 1 Experiments in recent years have tended to disprove the ex- acid portion is approximately half neutralized to give a istence of HvSO:. , or at least show they are present in infinitcsimally small concentrations in aqueous sulfur dioxide theoretically complete conversion of sulfurous acid solutions. The term sulfurous acid (H-SO.-t) as it is used in this (H2SO.,) to calcium bisulfite (Ca(HSO:,)2). In reality, descrihes undissociated sulfur dioxide in aqueous solutions. complete conversion to calcium bisulfite is never at- 90-- o(\] CO 80 UJ u QC 70 U. I < 60 H O h- 50 U. o H 40 Z UJ O 30 tr UJ Q. 20


Figure 1. Effect of pH on distribution of sulfur dioxide in solution. tained since the three forms overlap (Figure 1) to give condition is upset, calcium sulfite begins to precipitate some sulfurous acid and calcium sulfite. However, half- and continues to do so until equilibrium is restored. neutralization of the brine solution gives an optimal sul- Onset of precipitation may be detected by monitoring furous acid-calcium bisulfite ratio by minimizing cal- levels of sulfur dioxide, calcium, and pH. Appreciable cium sulfite formation and sulfur dioxide volatilization. changes in one or more of these factors will affect Adjusting the pH to give a clear brine does not pre- brined fruit quality. vent precipitation of calcium sulfite indefinitely. Small Variation in initial pH of brine solution within the amounts of calcium sulfite are formed in all brine solu- range of 2.5 to 3.3 and sulfur dioxide concentration tions^ but they remain temporarily soluble in a super- within 0.75 to 1.50% has little effect on retention of cal- saturated condition. Supersaturated solutions are un- cium and sulfur dioxide. There is a gradual decrease in stable and susceptible to temperature changes, seeding, concentration at all levels, with brine containing higher and nucleation of the precipitate by foreign solid mate- initial calcium and sulfur levels maintaining slightly rial introduced into the brine. Once the super.saturated higher levels throughout storage. Elevated temperatures are the primary cause of brine mental brine containing and calcium instability during storage, drastically reducing the level was acidified to pH 3.0 with citric acid and held of calcium (Figure 2) and sulfur dioxide (Figure eight weeks at 70° F. It retained essentially all of its 3). High temperatures also lower the pH. Low pH calcium and twice as much sulfur dioxide as a control coupled with reduced calcium levels may cause cracking sodium bisulfite brine acidified with hydrochloric acid. and softening of brined fresh fruit. Brines prepared Brines often are prepared in advance and held for and stored at cooler temperature (40° F) are more re- extended periods of time prior to use. This appears to sistant to deterioration. Calcium and sulfur dioxide be an undesirable practice due to brine instability. In losses incurred during storage should be corrected be- view of the changes occurring in brines during storage, fore fresh fruit is brined to assure high quality brined it is recommended that brines be used within 48 hours cherries. following preparation. If this is not convenient and ex- Brines should be prepared and used fresh to provide tended brine storage is necessary, calcium and sulfur maximum firming, bleaching, and preservation. A rapid dioxide losses should be determined and the brine re- method of preparation was given by Weast (1940). It adjusted to desired concentrations before brining fresh provides rapid preparation of brine by introducing fruit. liquid sulfur dioxide into a lime suspension. Using this Recommended levels of calcium ion in fresh brines procedure, brine can be prepared much faster than by range from 3,000 to 5,000 ppm, depending upon the va- the method of adding alkali slurry to sulfur dioxide riety and maturity of fruit. Additional calcium in the solutions. Both methods of preparation have essentially form of calcium chloride may be added to assist in firm- the same storage characteristics in terms of stability. ing the cherry. Brekke et al. (1966) suggest that calcium In laboratory brining trials at Oregon State Univer- also serves to inhibit enzymatic softening. They report sity, improved storage of brines has been achieved that addition of 2% calcium chloride by weight of fruit through use of chemicals which prevent precipitation of above the usual amount of calcium salts prevents enzy- calcium sulfite. Citric acid and citrate salts improve brine matic and non-enzymatic softening in brined cherries. stability by sequestering calcium ions and thus prevent- A rapid method for determination of calcium in brines ing formation of insoluble calcium sulfite. An experi- and brine adjustment is given later in this publication.


Figure 2. Changes in calcium content with time at different temperatures. 1.5

O I.0--

O 0.5- cr u

o.o 20 30 DAYS

Figure 3. Changes in sulfur dioxide content with time at different temperatures.

Preservative Properties of Sulfur Dioxide Solutions

Preservation of cherries and other brined fruit is more effective than bisulfite in controlling and made possible through the use of sulfur dioxide. The molds (Rehm and Wittmann, 1962). In fact, many in- preservative effect of sulfur dioxide is not permanent vestigators believe that the bisulfite and sulfite forms and is reduced or lost when the sulfur dioxide content is have little or no preservative properties. Rehm and Witt- lowered due to volatilization, oxidation to the ion, mann (1962) mentioned that the most common orga- precipitation as calcium sulfite, or combination with nisms are inhibited by 200 to 300 ppm sulfite, but with fruit_constituents as orgariic-bisulfite compounds. The notable exceptions. It is the more resistant microbial pH of sulfur dioxide solutions is perhaps the most im- strains that cause difficulty in commercial practice. Cruess portant single factor affecting preservation. (1932) found that at pH 3.5, two to four times as much Sulfur dioxide solutions are effective sulfur dioxide was required to inhibit microbial growth only at relatively low pH values (high hydrogen ion as at pH 2.5. At pH 7.0, sulfur dioxide was ineffectual concentration). This may be due to an extensive pene- on mold and , while 1,000 ppm was required to tration of microbial cell walls by un-ionized sulfur diox- inhibit bacteria. Rahn and Conn (1944) suggest that at ide where it acts to reduce essential enzyme high pH values the bisulfite ion functions to inhibit bac- linkages (Wyss, 1948). The most effective agents are teria but is not effective against yeasts. molecular sulfur dioxide (SO2) and sulfurous acid Yeasts which have been subjected to high concen- (H2SO3), both of which are present at low pH. Care- trations of sulfur dioxide for a period of time develop ful attention must be given to control of brine pH since a tolerance for SO2 and are able to grow and ferment shifts in pH profoundly affect the relative proportions under what would otherwise be abnormal conditions. The of the sulfur dioxide forms. For example, the concen- authors have observed yeast growth in brined cherries tration of sulfurous acid (HzSO.,) in a 0.5% sulfur with a pH of 3.3 and 3,200 ppm free sulfur dioxide dioxide solution at pH 3.0 is 5.91% or 295 ppm H2SO3. (98 ppm HoSOs). The fermentation was quite active At pH 4.0, the concentration of sulfurous acid de- and evolved copious amounts of dioxide, causing creases to 0.6% or 31 ppm HjSOs (Figure 4). gas pocketing and softening of the fruit. Yeasts are Sulfurous acid (H2SO.-,) inhibits yeasts, molds, and particularly resistant to sulfur dioxide once they have bacteria, but not with equal effectiveness since yeasts are attained a full fermentation rate. Amerine (1967) sug- the most resistant. Surfurous acid is 100 to 1,000 times gests this is due to fixation of sulfur dioxide by the PERCENT OF TOTAL FREE S02 — ro 0) -k cn o b b b b b


A /


(Q / C l^- / ro — / 3t « / z O 3 Q. in* / O) > or c 5* 13 -^ 3 I / i


DL 5* IP / oCA 0> r o 3

o) /

/ CD

/ cD metabolite, . Consequently, the arrest of ranging from 4 to 80 ppm. In commercial practice, fer- fermentation is often difficult, requiring unusually high mentation may occur in cherry brines containing as high levels of sulfur dioxide. as 98 ppm sulfurous acid. Observation and analysis of During curing and storage of brined cherries, the commercial samples of cherry brine over a wide range concentration of sulfur dioxide is reduced continually of pH and sulfur dioxide levels indicate 100 to 125 ppm through volatilization and combination with fruit sulfurous acid sufficient to provide preservation. and other- organic materials forming -bisulfite Large tanks and tote bins of fruit are particularly compounds. Joslyn and Braverman (1954) noted that vulnerable to microbial attack because of their large sur- the rate of sugar-bisulfite formation is influenced by pH, face area. This is especially true during warm temperature, ahd sugar content of the sulfur dioxide so- when sulfur dioxide losses are at a maximum and tem- lution. Although sugar-bisulfite compounds remain in peratures are optimum for microbial growth. Storage solution, they no longer have preservative properties. tanks are also susceptible to stratification; if tanks Yang et al. (1966) recommend a free sulfur dioxide are not sealed properly, dilution by rain water will raise content of 7,500 ppm to be maintained during storage the pH and reduce the sulfurous acid content. Stratifica- and shipping of brined cherries. This level of sulfur di- tion can be avoided by periodic circulation, which will provides preservation and allows for some loss help to maintain uniform conditions throughout the tank. prior to finishing. Free sulfur dioxide, pH, and sulfurous acid values It would be convenient for all concerned if it were should be determined at regular intervals as a quality possible to specify a minimum concentration of sul- control measure. If the sulfurous acid concentration furous acid above which complete preservation could drops below the critical level, adjustment should be be maintained. However, establishment of such a stand- made. This may be accomplished by careful addition of ard is prohibited by variations caused by storage tem- sulfur dioxide or acid in amounts sufficient to increase peratures, brining techniques, quality of fruit, and mi- the sulfurous acid concentration to a safe level. Soften- crobial load, and particularly those caused by microor- ing of the fruits may occur if the brine pH is reduced ganisms resistant to sulfur dioxide. Amerine (1967), below 3.0 for extended periods. A record of this infor- Joslyn and Braverman (1954), and Rahn and Conn mation for each tank would be helpful in maintaining an (1944) indicate inhibition of most common yeast and adequate concentration of sulfurous acid and avoiding bacteria is achieved bv concentrations of sulfurous acid fermentation and spoilage of the fruit.

Methods of Analysis

Sulfur Dioxide sulfur dioxide, gives a distinct blue-black endpoint with excess . Required reagents are: Methods of sulfur dioxide analysis can be divided into those designed to measure free sulfur dioxide and Iodine stock solution (1.56 N). Dissolve accurately those for total sulfur dioxide. Free sulfur dioxide, pres- weighed quantities of 198.4 g resublimed iodine (ACS) ent in its three forms, exists in the "free" state, that is, and 310.0 g iodine (C.P.) in a liter volumet- uncombined with organic plant materials. Total sulfur ric flask containing 250 ml distilled water. When the dioxide includes both free and bound sulfur dioxide. iodine is completely dissolved, make to volume with dis- Bound sulfur dioxide is liberated by alkali treatment or tilled water. Store all iodine solutions in an amber glass distillation and titrated simultaneously with free sulfur container away from light. Iodine is not stable in the dioxide. Since bound sulfur dioxide has no preservative presence of light, decomposing to hydriodic acid. High properties, only free sulfur dioxide will be used to esti- temperature storage will cause some volatilization of mate the effective preservative agent, sulfurous acid iodine. Therefore, it is necessary to restandardize iodine

(H2SO.,). solutions frequently.

Free Sulfur Dioxide Standard (0.1 N) sodium solution. Dissolve exactly 24.82 g of fresh - The following method is modified from that of the pentahydrate (ACS) and make to 1 liter with distilled Association of Official Agricultural Chemists (AOAC, water. This solution is used to standardize the iodine 1965) for determination of free sulfur dioxide. It con- solution. sists of a direct oxidation of sulfurous acid with stand- ardized iodine. The sample solution is acidified to liber- Starch indicator solution. Dissolve 1 g of water- ate sulfurous acid from its soluble salt forms and to soluble potato starch in 100 ml distilled water, heat to prevent release of organic-bound sulfur dioxide. The boiling, and cool. After preparation of the solution, add starch indicator, which is colorless in the presence of a few grams of and shake vigorously. This will retard mold growth. Discard solution if mold growth Sulfur dioxide equivalent (SDE). Defined as appears. parts per million sulfur dioxide per ml of iodine solu- tion used. Given the normality of iodine and volume of solution (20% v/v). Add 20 ml of sample solution, the SDE can be calculated. concentrated sulfuric acid (C.P.) to 80 ml of distilled water. SDE = Normality of iodine solution x 32,000

Standard iodine solution (0.156 N). Pipette 100 ml of sample solution ml of iodine stock solution (1.56 N) into a 1-liter volu- In the interest of accuracy and/or conservation of iodine metric flask and dilute to volume with distilled water. solution, it is often necessary to use less concentrated Standardize before using. iodine solutions or larger sample volumes. The SDE for several common sample volumes and normalities are Standardization of iodine solution. Transfer 10 given below. ml of standard sodium thiosulfate to a flask containing 100 ml distilled water. Add 1 ml of starch solution and Normality Brine sample size (ml) SDE five drops of 20% sulfuric acid. Titrate with the iodine to be standardized to the first permanent blue endpoint. 0.156 5 1,000 ' The normality of the iodine solution is calculated as 0.156 10 500 follows: 0.100 5 640 0.100 10 320 Normalitv of iodine = 10 ml :hiosulfate x 0.1 N 0.050 10 160 0.001 5 64 ml iodine required If the normality is high or low, add 1 ml distilled water The concentration of sulfur dioxide in parts per million or 0.65 ml of iodine stock solution, respectively, for each can be obtained by multiplying the ml of iodine required 0.001 N difference and restandardize with sodium thio- in by the SDE for the particular normality and sulfate. sample size used.

Determination of Free Sulfur Dioxide in Cherry Brine

Pipette 5 ml of the brine solution into a 250 ml 2. Determine parts per million (ppm) free sulfur Erlenmeyer flask containing approximately 100 ml dis- dioxide by direct iodine titration. tilled water. Add 1 ml of starch solution and five drops 3. Refer to Figure 4 and obtain the percentage sul- of 20% sulfuric-acid. Titrate with standardized 0.156 N furous acid corresponding to the pH of the sample solu- iodine solution until a blue color persists for 30 seconds. tion. Multiply the ml iodine required by 1,000 to obtain parts 4. Multiply ppm free sulfur dioxide by the percent- per million free sulfur dioxide, or by 0.1 to give percent age of sulfurous acid to obtain parts per million sulfu- free sulfur dioxide. rous acid. Example 1: Sulfurous Acid pH = 3.0 Utilization of free sulfur dioxide as a means of esti- SO, (ppm) = 5,000 (iodine titration) mating the effective preservation of brine is misleading % H2S03= 5.91% (from Figure 4) since the iodine titration does not distinguish between H2S03 (ppm) =0.0591 x 5,000 the three forms of sulfur dioxide in solution. Therefore = 295.0 it becomes necessary to use the pH in conjunction with the free sulfur dioxide concentration to determine if Example 2: sufficient sulfurous acid is present to insure preserva- pH = 3.7 tion. The sulfurous acid content of a sample solution SOo (ppm) = 5,000 (iodine titration) may be closely approximated in the following manner: % H2SO.H= 1.21% (from Figure 4) 1. Measure the pH of the brine sample with a prop- H...S03 (ppm) =0.0121 x 5,000 erly standardized pH meter. = 60.5 ppm From these examples it is apparent that effective Determination of calcium in cherry brine. preservation of sulfur dioxide solution, expressed in Transfer 1.0 ml of well-mixed brine sample into a 500 parts per million sulfurous acid (H2SO3), is appreci- ml flask containing 200 ml distilled water. Add 5 ml am- ably reduced by shifts in pH, even though the iodine monium hydroxide buffer, six drops indicator, and ti- titration for free sulfur dioxide remains constant. trate immediately to the blue endpoint.

ppm Ca++ = Calcium (ml EDTA used) (mg calcium/ml EDTA) (1,000)

The following is a modification of the AOAC method ml of sample for direct titration of calcium and with standard EDTA solution. The indicator, Eriochrome Preparation and readjustment of sulfur dioxide Black T, gives an orange-red color in the buffered sam- brines. Brine solutions prepared from liquid sulfur ple (pH 10) containing calcium. When sufficient EDTA dioxide must be partially neutralized with alkali before is added, the calcium is held in complex and the indi- use. Alkalies most commonly used are calcium hydroxide cator changes to light blue or greenish blue. In brines and calcium carbonate. The calculations given below are contaminated with , there is no endpoint. based upon addition of sufficient alkali to give one-half This method has been used satisfactorily for calcium neutralized sulfurous acid by theoretical complete con- titration in cherry brines containing 50 to 15,000 ppm version to calcium bisulfite, giving a final pH within calcium. Although both calcium and magnesium are 2.7 it 0.2. If the pH is not within this range, adjustment titrated simultaneously, magnesium is considered negli- should be made with small increments of sulfur dioxide gible in cherry brines since it is present only in trace or alkali. amounts. Calcium hydroxide and calcium carbonate are taken to be 100% pure. This provides a safety factor against Standard EDTA solution. Dissolve exactly 4.0 g over-neutralization of the sulfurous acid. of EDTA (disodium dihydrogen ethylenediamine tetra- acetate) in approximate!}' 800 ml distilled water. Adjust Preparation of fresh brine. Fresh brine is com- the pH to within 4.3 to 5.0 with and monly prepared by two methods: (1) Addition of al- make up to one liter with distilled water. One ml of this kali to sulfur dioxide solutions or (2) dissolving gaseous standard solution is equivalent to 0.4 mg calcium. sulfur dioxide in alkali solutions. The second method is the best one since it is much faster and wastes less sulfur dioxide to the atmosphere. Standard calcium chloride solution. Dissolve exactly 1.0 g of reagent grade calcium carbonate in 100 Pounds sulfur dioxide = ml 1 N hydrochloric acid. Bring solution to a boil, cool, and make up to one liter with distilled water. One ml of (% desired S02) (gal. brine) (8.4 Ibs./gal.) this solution contains 0.4 mg of calcium and is used to standardize the EDTA solution. 100 Pounds calcium hvdroxide = buffer-pH 10. Add 570 ml of concen- (% SO,)" (gal. brine) (4.85 Ibs./gal.) trated ammonium hydroxide (C.P.) to 67.5 g ammo- 100 nium chloride (C.P.) and make up to one liter with dis- tilled water. or pounds calcium carbonate = (%S02) (gal. brine) (6.55 Ibs./gal.)

Calcium indicator. Dissolve 0.2 g Eriochrome 100 Black T in 50 ml . Solution has a shelf of 5 months. Readjustment of stored brines. Stored brines often suffer losses of calcium and sulfur dioxide, thereby reducing the quality of the brined product. The chemical Standardization of EDTA solution. Transfer 10 constituents of the brine should be adjusted to their ml of standard calcium chloride solution into a 500 ml initial level prior to use. Stored brines stratify upon flask containing 200 ml distilled water. Add 5 ml am- standing and should be thoroughly circulated before monium buffer, six drops of indicator, and titrate im- sampling. mediately to the blue endpoint. Delay in titration will necessitate the use of additional indicator. If a sliding 1. Determine percent SO2 by iodine titration. endpoint occurs, dilute sample with distilled water. 2. Pounds SO;, to add = Mg calcium/ml EDTA solution = 4.0 mg calcium (% SO,. (lesirecI-% SO,, measured) CKKI. hrinc) (HA II>S./K;II.)

EDTA liter 100 3. Determine percent calcium by EDTA titration. These brine solutions will not become clear until ad- justed to a pH level below the recommended range. 4. Pounds calcium hydroxide to add = To obtain a clear brine within the desired pH range ++ ((%S02)(4.85))-((%Ca )(15.6)) x gal. brine (pH 2.7 ± 0.2), it is necessary to either reduce the sul- fur dioxide concentration or replace a small portion of 100 the calcium alkali (Ca(OH)2 or CaCOa) with sodium or for pounds calcium carbonate to add, substitute factor hydroxide. It is emphasized that the concentration of 21.0 for 15.6 in step 4. sulfur dioxide and calcium alkali should not be reduced below the amount which will give a clear and properly When brine solutions are prepared and/or adjusted adjusted brine. In any case, the calcium ion concentra- during hot climatic conditions, using warm water, it is tion should not be less than 3,000 ppm. frequently difficult to adjust the brine pH within 2.7 ± 0.2 without forming a white precipitate of calcium sul- fite. This condition is caused by a temperature-affected shift in the sulfur dioxide equilibria which necessitates ACKNOWLEDGMENT: The authors acknowledge use of additional Ca (OH)2 or CaC03 to achieve the the valuable advice and suggestions of Dr. Theran D. desired pH Jevel. Unfortunately this additional Ca(OH)2 Parsons, Department of Chemistry, Oregon State Uni- or CaCOs reacts to form an excessive amount of CaSOa. versity.

Literature Cited

Amerine, M. A., H. W. Berg, and W. V. Cruess. 1967. The Rahn, O., and J. E. Conn. 1944. Effect of Increase in Acidity on Technology of Making, 2nd ed. VVestport, Conn.: Antiseptic Efficiency. Ind. Eng. Chem., 36:185-187. AVI Publishing Co., Inc., 188-192. Rehm, H. J., and H. Wittmann. 1962. Z. Lebensm, Untersuch- AOAC. 1965. Official Methods of Analysis, 10th ed. Washing- Forsch, Ji5:413-429. ton, D. C.: Association of Official Agricultural Chemists. Walters, G. G., J. E. Brekke, M. J. Powers, and H. Y. Yang, Brekke, J. E., G. G. Walters, R. Jackson, and M. J. Powers. (rev. 1963). Brined Cherries: Analytical and Quality Con- 1966. Texture of Brined Cherries. U.S. Dept. of Agric, trol Methods. U.S. Dept. of Agric. ARS 74-23. ARS 74-34. Weast, C. A. 1940. Preparation of Solution to be Used in Brin- Cruess, W. V. 1932. Hydrogen-Ion Concentration in Preserva- ing Cherries. Western Canner and Packer, 32(6) :26-27. tive Action. Ind. Eng. Chem., 24:648-649. Wyss, A. 1948. Microbial Inhibition by Food Preservatives. Joslyn, M. A., and J. B. S. Braverman. 19S4. Chemistry of Sul- Adv. Food Res., 2:373-393. fur Dioxide, , and Their Organic Compounds. Adv. Yang, H. Y., E. Ross, and J. E. Brekke. 1966. Cherry Brining Food Res., 5:97-160. and Finishing. Ore. Agric. Expt. Sta. Cir. of Inform. 624.