juice and jelly quality from grapes grown in west …

JUICE AND JELLY QUALITY FROM GRAPES

GROWN IN WEST TEXAS

by

DONNA E. HUFFINGTON, B.S.

A THESIS

IN

FOOD TECHNOLOGY

Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for

the Degree of

MASTER OF SCIENCE

Approved

August, 1979

//^, 77 ACKNO^^^EDGMENTS

The author wishes to express sincere appreciation to

Dr. Robert C. Albin for serving as chairman of her graduate

committee.

The author also wishes to thank Dr. R. Max Miller for

his help and support in directing this research project.

Thanks are extended to Dr. M. L. Peeples for reading this

manuscript. Grateful acknowledgment is also due to Pro

fessor Robert R. Reed, Department of Plant and Soil

Science, for his helpful suggestions in carrying out this

research project.

Appreciation is extended to the Food Science and

Nutrition Institute for the financial support provided to

me for this work toward the Master of Science degree.

11

TABLE OF CONTENTS

ACKN0V7LEDGMENTS ii

LIST OF TABLES iv

LIST OF FIGURES v

I. INTRODUCTION 1

II. BACKGROUND 3

Grape Storage 5

Juice Extraction and Clarification 7

Spectroscopy 9

Jelly 9

Conclusion 12

III. MATERIALS AND T IETHODS 13

Juice 13

Jelly 21

IV. RESULTS AND DISCUSSION 23

Jelly 43

Conclusion 44

REFERENCES 45

111

LIST OF TABLES

1. °Brix of Grapes at the Time of Harvest 24

2. Weight Loss During the Washing and Destemming Process 25

3. Weight of Grapes, Juice, and Percent Yield of Juice from These Grapes Using Different Enzymes, Pectinol R-10, and Irgazyme 27

4. Ranking of Grape Varieties Combined with Enzymes Based on Percent Yield of Juice . . . . 29

5. pH and % Titratable Acidity of Purple Grape Juice Before and After Centrifuging and Before and After Treatment with Fining Agents Albumin, Bentonite Clay, and Casein 31

6. pH and % Titratable Acidity of Red Grape Juice Before and After Centrifuging and Before and After Treatment with Fining Agents Albumin, Bentonite Clay, and Casein 32

7. pH and % Titratable Acidity of White Grape Juice Before and After Centrifuging and Before and After Treatment with Fining Agents Albumin, Bentonite Clay, and Casein 33

8. Ranking of Treatments of Juices Based on Differences in Mean pH Before and After Centrifuging 35

9. Absorbance of Purple Grape Juices Before and After Centrifuging and Before and After Addition of Fining Agent; Mean , Standard Deviation and Variance of Absorbance of All Juices and All Juices Except Grand Noir 38

10. Absorbance of Red Grape Juices Before and After Centrifuging and Before and After Addition of Fining Agents 3 9

11. Absorbance of White Grape Juice Before and After Centrifuging and Before and After Addition of Fining Agents 40

IV

LIST OF FIGURES

1. Processing Steps from Grapes to Juice Extraction 16

2. Processing Juice with Fining Agents 18

3. Absorbance Scan of Commercial Grape Juices--Purple (1:10, Juice:Water), Red (1:10, Juice: Water), and White (1:2, Juice:Water)—in the Visible Light Spectrum 37

CHAPTER I

INTRODUCTION

Climatic conditions on the High Plains of West Texas

have been proven to be conducive to the production of grapes

Grape vines have grown well and produced good crops during

relatively moist seasons and very dry seasons in this area.

Rainfall is usually adequate for production of a grape crop

without requiring the use of irrigation water. These West

Texas conditions vary greatly from the conditions in the

primary grape growing areas such as California and New York.

Grapes are one of the most universally grown agricultural

products because they do seem to adapt well to most cli

matic conditions. However, these different conditions do

cause differences in the grapes.

Currently, several varieties of grapes are being grown

in West Texas in order to determine which ones are most

productive in the area. Many acres of land have been put

into grape production in the last few years and, if current

trends continue, there will be increasing acres of grapes

planted in West Texas in order to provide another source of

agricultural income for farmers of the area. Most of these

grapes are presently going into the wine industry in the

area. However, if grape production continues to increase,

it may be necessary to find another outlet for the grapes

which the wine industry in the area cannot use.

1

Therefore, this study has been designed to determine

how the growing conditions in West Texas, which are so dif

ferent from conditions in the primary grape-growing areas

of the country, will affect processing characteristics of

the grapes and whether an acceptable juice and jelly can be

made from West Texas grown grapes. In doing this, another

potential outlet for grapes will be shown to both growers

and industry.

CHAPTER II

BACKGROUND

Originally, grapes were grown only for home use. About

1900, the first plantings of grapes for commercial use were

established (Fisher, 1976). The processing of grapes into

juice for commercial use began in 1869 when a dentist. Dr.

Thomas B. Welch, and his son gathered grapes from their

trellis in New Jersey, prepared juice and pasteurized it in

hot water long enough to kill the yeasts (Pederson, 1971).

This was the beginning of an industry which has had a gradual

increase since 1869. The USDA has conducted extensive re

search with grapes beginning about 1900 (Magness, 1976).

Concord grape juice was the first to be preserved by pasteur

ization (Tressler, 1971). The procedure invented by Welch

involved hot pressing the crushed grapes, filling hot juice

into carboys which were then closed with paraffined corks.

The carboys were stored in a cool cellar for three months or

longer. During this period the pulp and other suspended

matter settled. The clear juice was siphoned off and filled

into bottles. The bottles were capped and placed in racks.

The racks of bottled juice were held in hot water, at 180 to

190° F for pasteurization. Dr. Welch was using the princi

ples expressed in Louis Pasteur's theory of pasteurization

(Pederson, 1971).

1

Grape juice is defined as the unfermented liquid ex

pressed from suitably ripened fruit of the grape (Pederson,

1971). Grape juice is essentially a solution of all soluble

ingredients of the fruit (Tressler and Joslyn, 1971). The

period during which grapes can be harvested is relatively

long; however, the juice extracted from these grapes will

not be the best unless they are harvested at the proper

times (Shoemaker, 1978). The refractometer is widely used

to give a quick sugar test for maturity. The sugar of

the berries consists of the invert sugars glucose and

fructose (components of sucrose). The optimum sugar level

differs with variety of grape but is commonly 20 percent

for processing into juice. Grapes do not increase in sugar

content after they are picked, therefore they must be

allowed to ripen to full maturity on the vine (McEachern,

1978). Time of ripening is dependent upon variety, geo

graphic location and climatic conditions (Flora, 1977).

Juice yield from ripe grapes is about 5 percent higher

than from unripe grapes (Pederson, 1971).

Grape juice differs little in chemical composition from

the grape berry except in crude fiber content and oils which

are primarily present in the seed (Pederson, 1971). Pederson

(1971) stated that in extracting juice, hot pressing of grapes

is essential in order to bring into solution the color and

other ingredients of the fruit. Hot-pressed juice is higher

in total solids, nonsugar solids and tannins than is cold-

pressed juice. The juice extracted does depend for composi

tion on variety of grape from which it is extracted, region

of production of the grape, cultural practices, weather fac

tors, and maturity (Sistrunk and Cash, 1974).

The method of extraction of the juice from the grape has

a marked effect on the composition of the prepared juice

(Tischer, 1951). The principal flavor components are sugars,

acids, and volatile esters, acids, alcohols, and aldehydes

(Pederson, 1971). Analysis by the Welch Grape Juice Company

has shown that grape juice contains potassium, sodium, cal

cium, phosphorus, iron, copper, magnanese, biotin, niacin,

panthothenic acid, pyridoxine hydrochloride, thiamin, folic

acid, ascorbic acid, choline, and trace amounts of riboflavin

and vitamin B,~. Sastry and Tischer (1952) found that grapes

contain anthocyanin pigments, chlorophyll, carotenes, and

water soluble yellow pigments.

Grape Storage

Methods for storage of grapes prior to processing have

been studied in order to allow grapes to be harvested at peak

maturity and held until processing is possible. .Storage tech

niques have been based on high humidity cold storage with

regular sulfur dioxide (SO2) 9^^ fumigations (Ryall and Harvey,

1959). Winkler and Jacob (1925) showed that several

preservatives could be used to prevent spoilage of grapes

under refrigeration (Winkler and Jacob, 1925) . Those pre

servatives included boric acid, formic acid, formaldehyde,

benzoate of soda, salicylic acid, and sulfur dioxide.

Sulfur dioxide in concentrations of 0.06 to 0.12% showed

indications of controlling alcoholic fermentation and the

production of acetic acid and retarded the activity of

microorganisms generally associated with grape spoilage.

Methods have been developed for applying sulfur dioxide to

commercial shipments of grapes (Smit et al., 1971) . In 1940,

tablets containing a mixture of sodium and potassium

bisulfite, sodium metabisulfite, alum, and silica gel were

used in shipping. Nelson and his co-workers (1966, 1968,

1970) reported the use of specially designed envelopes con

taining sodium bisulfite for rapid, then slow release of

sodium dioxide in grape containers. In 1968 and 1969, Smit

et al. (1971) experimented with the use of different packaging

materials and different concentrations of sulfur dioxide. An

acceptable product could be maintained for about two months

with sodium bisulfite in cellophane containers and storage

at 32°F (0°C).

In 1977, Hedberg reported a marginal reduction of mold

development in stored grapes to which field applications of

benomyl had been made during the growing season. He also

found that in-container sulfur dioxide generators produced

a level of sulfur dioxide suitable for long-term storage of

grapes. Also, perforated polyethylene liners act as a mois

ture and sulfur dioxide barrier without causing undesirable

condensation.

The use of freezer temperatures to extend storage life

of grapes has been studied by Siewart et al. (1951) and

Woodroof et al. (1956) . Both of these described the use of

frozen deseeded grapes for use in pastries and other products.

However, these grapes had been heat-processed prior to freez

ing which resulted in a cooked flavor. In 1971, Harris

reported the pressing of good quality juice from crushed un

cooked grapes which had been held at -18°C for periods up

to 15 months. Woodroof et al. (1956) described juice pressed

from previously frozen grapes as superior in color and flavor.

Freezing grapes prior to juice extractions has been shown to

give increased yields and pigment extraction (Flora, 1976).

Varietal and processing differences will affect the accept

ability of the product pressed from frozen grapes. Freezing

whole grapes requires minimum preparation and will maintain

quality much better than other methods over extended storage

periods.

Juice Extraction and Clarification

Juices may be extracted from either cold or heated fruit

(Shoemaker, 1978). The conventional method of juice prepara

tion used by the industry is to heat grapes to 58-61°C

8

followed by enzyme hydrolysis (Sistrunk and Cash, 1974). At

higher temperatures excessive tannins and harsh flavor are

extracted from the seeds (Cruess, 1958).

Freshly expressed grape juice is supersaturated with

potassium acid tartrate (argols) (which gives the juice a

harsh acid flavor) and tannins and colored substances which

give the juice a cloudy appearance (Lopez, 1969). The heat

ing process brings these substances into solution (Shoemaker,

1978; Sistrunk and Cash, 1974; Tufail and Bhatti, 1973; Ishii

and Yokotsuka, 1972; Neubeck, 1959). According to Smock and

Neubert (1950) this material constitutes mucilagenous hydro-

philic gums and pectinous materials. The pectic substances

are widely distributed in grapes and in the natural state are

insoluble in water (Neubeck, 1959). The pectin in juice tends

to keep small insoluble particles suspended in a colloidal

system resulting in a cloudy or hazy juice (Neubeck, 1959;

Smock and Neubert, 1950). Clarification of the juice requires

the splitting of the colloidal system by aid of chemical or

mechanical fining agents (Tufail and Bhatti, 1973). Cruess

(1958) describes a fining agent as a substance which when

added to the liquid to be clarified, will form a precipitate

which settles and carries with it the finely divided particles

responsible for the cloudy appearance. In order to break

down the colloidal system produced by the pectin, pectolytic

enzymes have been used (Joslyn et al., 1952; Neubeck, 1959;

Tufail and Bhatti, 1973; Ishii and Yokotsuka, 1972; Flora,

1976; Sistrunk and Cash, 1974). Flora (1976, 1977) described

the use of Pectinol (Rohm and Hass, Co) and Sistrunk and Cash

described the use of Irgazyme (Ciba Geigy Corp.) pectinase

enzymes in clarifying grape juice.

Spectroscopy

A spectrometer may be used for determining clarity of

juice by measuring the amount of light dispersed by suspended

matter (Cruess, 1958). All spectroscopy instruments contain

the same basic components: a source, an attenuating device,

a monochromater, a cell to hold the sample, a detector and

amplifier, and a meter or recorder to observe the signal

(Pomeranz and Meloan, 1978). The simplest is a single beam

instrument. However, double beam instruments are more ac

curate and reliable. This instrument splits the source radia

tion into two beams. Half the time the beam passes through

the reference cell containing everything except the sample

and half the time the beam passes through the sample cell.

Any fluctuations in source or solvent will be registered both

by the sample and the reference. The detector will measure

the difference between the signals which will be .due entirely

to the sample.

Jelly

Jelly is defined in the United States as the semi-solid

food made from not less than 45 parts by weight of fruit juice

10

ingredient to each 55 parts by weight of sugar (Desrosier,

1970). Jelly is one of the most popular uses for fruit by

products because it can be made from under-ripe, undersize,

and off-grade fruit (Woodroof, 1975). The fruits used are

of good quality but are not attractive to the sight, there

fore cannot enter the fresh market channels (Desrosier, 1970).

Jelly is prepared by combining fruit juice, sugar, pec

tin, and acid in the proper amounts and concentrating by

evaporation to such a consistency that gelatinization takes

place on cooling and microbial spoilage cannot occur (Cruess,

1958; Desrosier, 1970). Of these ingredients, pectin is the

most important in forming a gel. In jelly preparation, the

sugar disturbs the pectin-water equilibrium and causes the

pectin to precipitate as a hydrated colloid which forms a

network of fibrils throughout the mass binding the sugar

syrup into a gel. The density of this network and, there

fore, the strength of the gel depends on the concentration of

pectin. Also, the more concentrated the sugar solution, the

less water there is for the gel to support producing a stiffer

texture. If the sugar content is too low, the jelly will be

tough; if the sugar content is too high, the jelly will be

soft (Woodroof, 1975). Acid causes the jelly to'be firmer,

probably by toughening the fibrils. Too much acid causes

inelasticity of the fibrils and too little acid causes weak

fibrils. Neither of these will support the gel structure

11

and result in syneresis (weeping) of the final product

(Cruess, 1958).

Federal Standards require jelly to be made on the basis

of 45 parts-standard fruit juice per 55 parts sugar (Lopez,

1969). Standard grape juice contains 14.3 percent soluble

solids. This is concentrated by cooking to not less than

65 percent soluble solids in the finished product. Maximum

jelly strength is attained at 65-69 percent soluble solids.

During the boiling, it is necessary to skim off the foam

which forms on the top in order to produce a product with a

good appearance (Woodroof, 1975). A refractometer enables

the determination of the soluble solids content. The boil

ing point of a 65 percent sugar solution is 219-221^ F and

may be used as an indication of proper concentration of the

jelly.

When boiling and concentrating is completed, the hot

liquid is poured into jars and allowed to set. The heat of

the boiling liquid is usually sufficient to eliminate spoil

age organisms. Too much agitation before the jelly has set

injures the formation of the physical structure (Prescott

and Proctor, 1937). Improper processing of grape jelly may

result in a poor product. Sugar crystallization may be

caused by too much sugar, too little acid, overcooking of

jelly or delay in sealing the jelly container. Cloudiness

is caused by using cloudy juice. An improper balance of

12

pectin, acid, and sugar may cause failure of the jelly to

jell (Woodroof, 1975). Using too little sugar or boiling

after the jellying point has been reached will cause jelly

to be tough or stringy (Thrash, 1968).

Conclusion

High costs associated with production and harvesting

and the lack of a concentrated growing area have hampered

development of a processing market for grapes (Flora, 1977).

Increased grape plantings in recent years have caused sur

pluses for the wine industry. Therefore, other processing

outlets are being sought to absorb the projected increase

from more recent plantings of grapes. Marketing of com

mercial processed juice and jelly show promise for expanded

use of these grapes.

CHAPTER III

MATERIALS AND METHODS

Juice

Grapes were gathered from two vineyards in the West

Texas area over a two-year period. Harvesting was done

during the months of August, September, October, and early

November because grapes in this area ripen and are ready

for harvest during these months. The actual time of harvest

depends on grape variety and climatic conditions during the

growing and ripening season. Varieties were chosen for

harvesting based first on availability and next on advice

of the growers. From the suggested varieties, selections

were made for color to enable the study of purple, red, and

white grape juices. For the most part, different varieties

were available each of the two harvest seasons due to the

very different conditions during the two growing and ripen

ing seasons, one of which was rather cool and moist (1977)

and the other of which was very hot and dry (1978). However,

both years it was possible to obtain samples from varieties

of the three colors.

Once the variety decisions were made, grapes of those

varieties chosen were checked twice a week near and during

the harvesting season for soluble solids content. This was

accomplished by randomly selecting 10 grapes from 3 or 4

13

14

different vines of that variety and determining the average

percent soluble solids in "Brix by use of a hand-held Abbe

refractometer (National No. 15666, 0-32% soluble solids or

°Brix). When the grapes of each variety reached at least

20° Brix, a half-bushel basket full of grape bunches was

harvested by hand randomly from several vines of that variety

and taken to the Texas Tech University Food Technology Depart

ment pilot plant for processing.

On arrival at the pilot plant, the grapes were weighed,

including adhering dirt and trash. They were then washed in

a sink of cool water. Upon removal from the water, individ

ual grapes were removed from clusters by hand, discarding

damaged and shriveled grapes along with stems and leaves.

The sound grapes were put on cheesecloth on a mesh table to

allow for evaporation of excess water. A fan was used to

circulate air more quickly and speed the evaporation process

before leakage of juice from the grapes could begin. Grapes

were put in large clear plastic bags which were then closed

and labeled. These bags of grapes were put on racks in a

freezer room which was maintained at 0°F. They remained in

the freezer room until time for further processing. The

length of storage has been shown not to affect quality of

products made from frozen grapes (Flora, 1976). The grapes

in this study were kept from one to fifteen months.

Of the varieties from which samples were harvested, the

results of ten are presented in this thesis. Samples from

15

the other varieties were used in trying methods other than

the one presented in the Materials and Methods section of

this thesis.

Before further processing, grapes were allowed to thaw

at room temperature for approximately 24 hours. The first

steps in the actual processing were to divide the grapes into

two approximately equal amounts, add an enzyme to each, and

extract the juice (Fig. 1). Two different enzymes, Irgazyme

(Ciba Giegy) and Pectinol R-10 (Rohm and Hass), were used in

this study. The portion of the grapes with which Irgazyme

was used was allowed to set for at least four hours at room

temperature after the addition of the enzyme which was added

on the basis of 0.0375 gm of enzyme per 908 gm of grapes.

At the end of this period, the grapes were put into a 5 1/2

quart china cap with wooden roller (Wearever #4700) and the

juice pressed from them by rotating the wooden roller.

As shown in Fig. 1, when using Pectinol R-10, it was

necessary first to heat the grapes to 135°F and hold at this

temperature for ten minutes. The temperature was then raised

to 145°F where it was held for another ten minutes. At the

end of this time, the Pectinol R-10 was added on the basis

of 28.4 gm of enzyme per 908,000 gm of grapes. This was

held at 145°F for an additional 30 minutes after which these

grapes were put into a 5 1/2 quart china cap and the juice

pressed from them by rotating the wooden roller.

Irgazyme (70°F - 4 hours)

Extract Juice

16

Thawed Grapes

i Heat

(135°F - 10 minutes)

Heat

(145°F - 10 minutes)

I Pectinol R-10

(145°? - 30 niinutes)

Extract Juice

Fig. 1. Processing steps from grapes to juice extraction

Further processing was accomplished as shown in Fig. 2.

The juice extracted from each variety of grape was divided

into four samples, one of which was bottled and heat pro

cessed in a hot water bath at 175°F for 30 minutes in order

to stop enzymatic activity and preserve the juice for storage.

A 2 percent egg albumin in warm water solution was added

on the basis of 5 ounces of albumin per 25 gallons of juice.

The albumin was purchased as a dry powder and dissolved in

enough warm water (approximately 100°F--not hot enough to

coagulate the egg albumin) to make a 2 percent albumin solu

tion for each sample. After adding the albumin solution to

the grape juice, this mixture was heated to 175°F to coagu

late the albumin and stop enzymatic activity. This was

allowed to settle for at least 48 hours at which time the

clear supernatant layer was poured off. This was bottled

and processed at 175°F for 30 minutes in a hot water bath.

The third sample (Fig. 2) was heated to 175°F for one

minute to stop enzymatic activity. To this juice was added

a 2 percent casein solution on the basis of 5 ounces of

casein per 25 gallons of juice. The casein solution was pre

pared by soaking the desired amount of casein powder in an

ammonium hydroxide solution prepared by diluting 1 part con

centrated ammonia in 20 parts distilled water. This casein-

ammonium hydroxide solution was heated until no more ammonia

18

Extracted Juice

Sample 1

bottle Egg Albumin (2%)

i Heat

Pasteurize to (175°F - 30 min.) 175°F

I Settle

(70°F - 48 hrs.)

Bottle

Pasteurize (175°F - 30 min.)

Sample 4

Heat to

175°F

Casein (2%)

I Settle

(70°F - 48 hrs.)

Heat to

175°F

Bentonite Clay (5%)

i Hear to

140°F Bottle I

Settle

(70°F - 48 hrs.) Pasteurize

(175°F - 30 min.) Bottle

i Pasteurize

(175°F - 30 min.)

Fig. 2. Processing juice with fining agents

19

fumes were detectable from it. The resulting material was

diluted to 2 percent casein in water. This 2 percent solu

tion was added to sample 3, mixed well and allowed to setnle

without agitation for 4 8 hours. The supernatant layer was

removed, bottled, and processed for 30 minutes at 175°F in

a hot water bath.

As indicated in Fig. 2, sample 4 was heated to 175°F

to stop activity of the enzyme. A bentonite clay suspension

was added to this juice on the basis of 3 gm bentonite clay

per liter of juice. This bentonite clay was purchased as a

dry powder and made into a suspension by placing 5 gm of clay

in a bottle and making up to 100 milligrams with distilled

water and shaking well. This was agitated frequently and

kept for at least three days prior to its use in order to

assure a good suspension. The desired amount of this sus

pension was weighed and added to sample 4, mixed well and

allowed to set for 48 hours without agitation. The clear

layer was poured from the top, bottled, and processed in a

hot water bath for 30 minutes at 175°F.

All juice samples were held at 40°F until ready for

testing.

Aliquots were taken from each juice sample for deter-

minination of pH, percent titratable acidity, and absorbance;

pH was determined by use of a Beckman Model 3 500 digital pH

Meter (Beckman Instruments, Inc., Fullerton, California).

20

Percent titratable acidity was determined by titrating an

18 gm sample with 0.1 N NaOH to the phenolphthalein end

point of pH 8.3 as determined by the use of a Beckman Model

3500 Digital pH Meter. The number of milliliters of 0.1 N

NaOH used for the titration was used in the following formula

to determine the percent titratable acidity:

ml 0.1 N NaOH x 0.0075 % Titratable Acidity = • x 100

gm Sample

All acid titrated in this juice was calculated as tartaric

acid:

COOH I

H-C-OH J eq wt 7 5

HO-C-H

k :ooH Absorbance of the samples was determined by a Beckman lodel

35 Spectrophotometer with Recorder (Beckman Instruments,

Inc., Irvine, California). Prior to running absorbance tests

on the experimental samples, samples of commercially prepared

purple, red, and white juices were each scanned to determine

the optimum wavelength settings for determination of absorb

ance on the test juices. As a result of those scans, a set-

ting of 450 nm was chosen for all samples and absorbance was

read directly from the digital display readout.

The grape juice samples were then centrifuged in a

VWR Scientific Centrifuge Model 6F-8 at 1000 rpm for 20 minutes.

21

Aliguots were again taken for pH, percent titratable acidity

and absorbance. These tests were performed in the manner

as done with the aliquots of the samples before centrifuga-

tion.

Remaining clarified juices of samples chosen on the basis

of color were stored in refrigeration storage for later

processing into jelly. No light colored juices were stored

for this purpose because there would be little commercial

value of jellies made from these juices.

Jelly

The first step in. making jelly was the determination

of the soluble solids content of the juice to be used. This

was done with the use of a Kerno No. 5532 hand-held refrac

tometer calibrated to read from 0 to 90 percent soluble

solids. By definition, standard grape juice contains 14.3

percent soluble solids and jelly production requires 45 parts

standard juice per 55 parts sugar. Therefore, the amount of

sugar needed is based on grape juice containing 14.3 percent

soluble solids. In calculating the amount of sugar required,

adjustments for soluble solids contents were made by use of

the following:

14.3 Soluble solids of juice to be used

45 _ (Weight of juice) (factor) ^ 3 ~ X

X = amount of sugar needed

= factor

22

The amount of pectin required was based on the amount of

sugar used. The pectin was 100 grade; therefore, it was

added on the basis of 1 part pectin per 100 parts sugar.

The amount of acid required was determined by titrating

a 22.7 ml. sample of each juice to pH 3.3 with a 0.25 per

cent tartaric acid solution. The milliliters of tartaric

acid solution multiplied by 200 was the milliliters of acid

required per pint (454 gm) of jelly.

Once the amounts of constituents required had been

determined, the juice was put into a steam jacketed ketrle.

The pectin was mixed with a small amount of the sugar and

stirred into the juice. This juice-sugar-pectin mixture was

heated to boiling, at which time the remaining sugar was

added. Boiling was continued until the mixture was concen

trated to contain 65 percent soluble solids as determined

by a Kerno No. 5532 refractometer. The required amount of

acid was put into pint jars and the hot jelly mixture at

65 percent soluble solids poured on top of the acid. The

jars of jelly were allowed to set without agitation for

24 hours for complete jelling to take place. They were then

kept at room temperature for one week at which time the con

tents were checked by visual observation for clarity,

syneresis, and jelling.

CHAPTER IV

RESULTS AND DISCUSSION

As shown in Table 1, all grapes with the exception of

the Veeport variety were between 20 and 25° Brix (percent

soluble solids) when checked in the vineyard at the time of

harvest. Veeport grapes were harvested at 19.9° Brix which

was considered close enough to 20° Brix to justify harvest

at that time. Stuben was the only variety from which samples

of the two growing seasons were used with the processing

method previously described in the Materials and Methods

section. These grapes had a higher percent soluble solids

during the hot dry year (1978) than when conditions were

cooler and more moist (1977) during the growing and ripening

season.

Table 2 shows the weight of grape clusters harvested

for each variety and the weight of grapes after washing,

destemming, and removing leaves and shriveled grapes.

Table 2 also shows the calculated percent weight lost during

these procedures and this is the most significant part of

this table. These percent losses in weight ranged from 2.32

with SV12-309 to 14.08 with the Grand Noir variety.. Differ

ences in percent weight loss are caused by size and there

fore, weight of stems, adhering leaves, and shriveled or

unformed grapes which must be discarded.

23

24

TABLE 1.—°Brix of grapes at the time of harvest

Variety °Brix

Buffalo 20.1

Carmen 21.8

Camay 22.8

Golden Muscat 22.0

Grand Noir 2 4.6

New York Muscat 21.7

Stuben (1977) 21.7

Stuben (1978) 23.6

SV 12-309 21.6

Veeport 19.9

25

TABLE 2.—Weight loss during the washing and destemming process

Variety

Buffalo

Carmen

Camay

Golden Muscat

Crand Noir

New York Muscat

Stuben (1977)

Sti±)en (1978)

SV 12-309

Veeport

weight of Crape Clusters

(gm)

6615

8095

12465

11085

8400

5280

6750

7390

9410

6220

Wei Aft

ght of Crapes .er Destemming

6262

7514

12012

10242

7217

4872

6352

6940

9192

5907

Percent Weight: Loss

5.34

7.18

3.63

7.60

14.08

7.73

5.90

6.10

2.32

5.03

27

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28

the 1977 crop of Stuben grapes which had a juice yield of

47.28 percent with Irgazyme and 44.16 percent with Pectinol

R-10—a difference of 3.12 percent. The 1978 crop of Stuben

grapes exhibited a similarly close percent juice yield with

the two different enzymes with a difference of only 4.35 per

cent between the use of Irgazyme giving a juice yield of

60.14 percent and Pectinol R-10 giving a juice yield of

55.79 percent. The average difference in percent juice

yield is 14.65, with Irgazyme giving an average of 57.45

percent and Pectinol R-10 giving a juice yield of 42.80

percent. This large difference could make a substantial

difference to the grape processor who wants to extract the

largest amount of juice from the purchased grapes.

The ranking of the grape varieties and enzymes used

are shown in Table 4. Ranking is based on the percent juice

yield ranging from greatest to least percent yield. None

of the grape batches on which Pectinol R-10 was used ranked

in the top quarter (first 5) and only two ranked in the top

half. Those two were Stuben (1978), ranking number 6, and

Veeport, ranking number 9. However, Stuben (197 8), using

Irgazyme ranked number 5 and Veeport using Irgazyme ranked

number 4, both ahead of that same variety using Pectinol

R-10. The poorest ranking for a grape using Irgazyme was

Carmen which ranked 15 with a 44.07 percent juice yield.

However, when-Pectinol R-10 was used with this variety, ir

TABLE 4.—Ranking of grape varieties combined with enzymes based on percent yield of juice

Grape Variety Enzyme

SV 12-309

New York Muscat

Golden Muscat

Veeport

Stuben (1978)

Stuben (1978)

Grand Noir

Camay

Veeport

Buffalo

Stuben (1977)

SV 12-309

Golden Muscat

Stuben (1977)

Carmen

Grand Noir

Camay

Carmen

Buffalo

New York Muscat

Irgazyme

Irgazyme

Irgazyme

Irgazyme

Irgazyme

Pectinol R-10

Irgazyme

Irgazyme

Pectinol R-10

Irgazyme

Irgazyme

Pectinol R-10

Pectinol R-10

Pectinol R-10

Irgazyme

Pectinol R-10

Pectinol R-10

Pectinol R-10

Pectinol R-10

Pectinol R-10

Ranking i Juice Yield

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

67.59

67. 09

63.64

60.59

60.14

55.79

55.37

54.65

54.42

54.10

47.28

46.85

44.58

44.16

44.07

42.67

40.39

37.14

36.72

25.32

30

ranked 18 with a juice yield of 37.14 percent. With all

varieties, the batch using Irgazyme ranked higher than that

same variety when Pectinol R-10 was used which means that

the Irgazyme gave a greater percent yield than did Pectinol

R-10 with all grape varieties.

As pointed out earlier, the percent juice yield from

grapes is of great importance to the grape processor. There

fore, Irgazyme would be the enzyme chosen based on the data

thus far presented. For this reason, further data will be

presented only on juice which was extracted with the aid of

Irgazyme pectinase enzyme.

Tables 5, 6, and 7 show the pH and percent titratable

acidity of the Irgazyme-extracted purple, red, and white

juices before and after the addition of fining agents and

before and after centrifugation. There was little change

in pH shown with the largest difference in mean pH between

centrifuged and non-centrifuged samples of the same type

(i.e., bentonite non-centrifuged versus bentonite centrifuged)

being 0.08 pH change. This occurred with white grape juice

(Table 7) in which Irgazyme alone was used and when Irgazyme

was used in combination with casein. When Irgazyme alone

was used, the pH changed from pH 3.79 with a standard devia

tion of 0.07 and variance of 0.003 in the ncn-centrifuged

sample to pH 3.87 with a standard deviation of 0.09 and

variance of 0.004 in the centrifuged sample. When Irgazyme

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34

and casein v/ere both used, the change was from pH 3.82 with

a standard deviation of 0.08 and variance of 0.003 before

centrifuging to pH 3.90 with a standard deviation of 0.01

and variance of 0.00003 after centrifuging. As shown in

Table 8, difference in the mean pH ranged from these two

with 0.08 percent difference to purple juice with which

Irgazyme and bentonite clay were used. This juice showed

no difference in pH before and after centrifugation having

a pH of 3.88 in both sample types with a standard deviation

of 0.06 and variance of 0.003 before centrifuging and

standard deviation of 0.06 and variance of 0.002 after

centrifuging. Overall, the change in mean pH was quite

small when the juices were centrifuged with 67 percent show

ing less than 0.05 pH change (Table 8).

The mean pH's covered a relatively narrow range from

pH 3.77 to pH 3.93. Likewise, the percent titratable acidity

of these juices covered a narrow range from 0.45 percent to

0.63 percent. Since both are measures of acid, it would be

expected for both to be relatively close in value if either

is close.

When looking at individual grape varieties in Tables 5,

6, and 7, varietal differences can be seen. For example,

while Veeport and Buffalo are both purple grapes, zhe pH of

Veeport grapes was near pH 3.80 while the pH of Buffalo

grapes was near pH 3.90 (Table 5). In the red juices

35

TABLE 8.—Ranking of treatments of juices based on differences in mean pH before and after centrifuging

Percent Difference Grape in Mean pH Ranking Color Treatment

0.08 1.5 White Irgazyme w/casein

0.08 1.5 White Irgazyme

0.05 3.5 Purple Irgazyme

0.05 3.5 Red Irgazyme w/albumin

0.04 5.5 White Irgazyme w/bentonite

0.04 5.5 Red Irgazyme w/bentonite

0.03 7.5 White Irgazyme w/albumin

0.03 7.5 Red Irgazyme w/casein

0.02 9 Purple Irgazyme w/albumin

O.Ql 10.5 Red Irgazyme

Q.Ol 10.5 Purple Irgazyme w/casein

0.00 12 Purple Irgazyme w/bentonite

36

(Table 6), the juice from the 1978 crop of Stuben grapes

had a pH near 3.60 while the New York Muscat had a pH close

to 3.90. This indicates that pH and percent titratable

acidity are more variety dependent than color dependent.

As described in the Materials and Methods section,

samples of commercial purple, red, and white juices were

purchased and scanned in order to determine the proper

absorbance setting for use as a measure of juice clarity.

The results of those scans are shown in Fig. 3. It was

necessary to dilute the purple and red juices to 1:10 juice

to water in order to scan them. The white juice was diluted

to 1:2 with water. All three juices exhibited a flat ab

sorbance in the 450 nm range; therefore, this was selected

as the wavelength setting for determining the absorbance

of the test juice samples. Results of the absorbance test

ing at 450 nm for purple, red, and white juices are shown

in Tables 9, 10, and 11, respectively. These juices were

divided into the three groups for comparison of absorbance

results because of the influence of color on the absorbance

as shown by the mean absorbance of samples before centrifug

ing or adding any of the fining agents. Purple juices had a

mean absorbance of 3.63, with a standard deviation of 2.60

and variance of 5.42, red had a mean absorbance of 1.87,

with a standard deviation of 1.70 and variance of 1.93, and

white had just 0.27 mean absorbance with a standard deviation

of 0.23 and variance of 0.03.

37

• Purple

350 400 450 500 550 600

Wavelength in nm

650 700 750

Fig. 3. Absorbance scan of commercial grape juices—purple (1:10, juicerwater), red (1:10, juice:water), and white (1:2, juice:water)--in the visible light spectrum

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41

In the purple juices (Table 9) the mean absorbance, the

standard deviation, and variance were greatly reduced by

the elimination of Grand Noir juice from the calculations.

This is an extremely dark juice which produced absorbance

readings which were considerably higher than the other purple

juices. Because of its dark color, this could be a good

juice to mix with other grape juice which is lacking in

color.

The mean absorbances indicate that allowing the juices

to settle for 48 hours and removing the supernatant layer

produced a clearer juice than did the centrifuging of the

juices. For example, a mean absorbance of 3.63 was obtained

when juice with Irgazyme was allowed to settle and a mean

absorbance of 3.87 was obtained with this same juice after

centrifuging (higher absorbance indicates less clear juice).

The mean absorbance of the purple juices was higher after

centrifuging with all fining agents except albumin. When the

samples in which albumin was used were centrifuged, the mean

absorbance was reduced from 3.29 to 3.28, which indicates

essentially no change in clarity.

Definite varietal differences can be seen through these

absorbance readings. For example, when bentonite clay was

used as a fining agent in the Irgazyme extracted juices of

Buffalo and Veeport grapes, the absorbance was reduced both

before and after centrifuging while that same procedure

42

increased the absorbance of Grand Noir juice. Although

there are varietal differences, it appears that the best

average method for use with purple juices would be the

addition of albumin as a fining or clarifyijg aid.

Table 10 deals with red juice absorbance which

shows that the juice from the 1977 harvest of Stuben grapes

was not clarified as well as that from the 1975 harvest.

This is the only area studied in which there was any real

difference seen between the two years harvest of this grape

variety. As with the purple juices, the mean absorbances

of the red juices indicate that the use of albumin as a

clarifying aid did produce a clearer red juice than the

other methods. The albumin-clarified juices produced a mean

absorbance of 0.89 with a standard deviation of 0.88 and

variance of 0.52 before centrifuging and mean absorbance of

0.87 with a standard deviation of 0.67 and variance of 0.30

after centrifuging. These standard deviations and variances

which are so close to the same value as the means indicate

the absorbance values are varietal dependent.

Table 11 shows that the use of bentonite clay as a clari

fying agent produced a clearer white juice than the other

methods based on absorbance. However, little difference

was observed between the absorbance when bentonite clay

was used or when albumin was the clarifying agent. The

absorbance differences are just 0.03 before cenrrifuging

43

and 0.07 after centrifuging. Therefore, either of these two

agents, bentonite clay or albumin, could be considered good

clarifying agents for use with Irgazyme-extracted white grape

juices.

Jelly

Although the primary purpose of this study was the

clarification of juices extracted from grapes grown in West

Texas, an attempt was also made to determine whether jelly

could be made from these juices. As stated in the Materials

and Methods section, no attempt was made to produce jellies

from any red or white juices. Jellies were only evaluated

visually to determine whether they met quality standards as

described in the Background section of this thesis.

No varietal differences were seen in the jellies as

long as the proper amount of juice, sugar, pectin, and acid

were used as previously described. When a portion of jelly

was removed from its container and placed on a flat surface,

the jelly retained its shape. There was no evidence of

syrupy, sticky, or gummy jelly. When cut, the jelly was

tender and left a smooth cut surface. No syneresis was

observed either in the jelly surface in the jar or after the

jelly was removed from the jar. The jelly had a clear spark

ling appearance. These statements were true of all jellies

made from the purple juices of this study. (The Grand Noir

juice was not used because of its extremely dark color.)

44

Conclusion

Results of this study have shown that it is possible

to make a clear juice from grapes grown in West Texas. In

order to do this it is necessary to use a pectinase enzyme

during the extraction process in order to break down the

pectin structure and allow the substances held in colloidal

suspension to settle out of the juice. Irgazyme was found

to be the best pectinase enzyme for this purpose. This

enzyme also allowed for the extraction of a greater amount

of juice from the grapes.

Along with the enzyme, it was preferable to use a fining

agent or clarifying aid in order to help settle the suspended

particles once the pectin structure was destroyed. Overall,

albumin was found to be the best substance for this purpose.

However, bentonite appeared to be slightly better for use

with white grape juices.

Once a clear juice was obtained, it was possible to make

a clear sparkling jelly from this juice. Purple juices were

the only ones used for this purpose. These jellies met good

visual quality standards.

Therefore, grapes grown in West Texas have been shown

to have processing potential as juice or jelly. "These could

provide another source of agricultural income to the High

Plains of West Texas.

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