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An ice cream laboratory guide

Chapter 39: EXERCISE NUMBER XXVIII BACTERIAL COUNTS OF ICE CREAM
By W. W. Fisk
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About This Book

A laboratory manual guides students through the scientific manufacture of frozen desserts, combining equipment descriptions, sanitation practices, and stepwise laboratory exercises. It explains methods for standardizing mixes and testing fat and solids, the use of stabilizers, and principles of freezing, hardening, and measuring swell (overrun). Practical recipes and procedures cover plain, fruit, nut, custard, parfait, and molded products, ices and sherbets, and related preparations; supplemental exercises address microbial counts, gelatin testing, varying ingredients and processing treatments, judging criteria, and visits to commercial plants for applied observation.

EXERCISE NUMBER XXVI
THE EFFECT OF THE TEMPERATURE OF THE MIX
AS IT ENTERS THE FREEZER ON THE SWELL

Make enough mix for four 10 gallon batches of ice cream, using the following formula:

  • 40 pounds of 20% cream
  •  8 pounds of sugar
  •  4 ounces of vanilla extract
  •  4 ounces of gelatin in 4 pounds water.

Freeze the first batch as a preliminary one. Have the second at a temperature of 40 degrees F., when it enters the freezer, the third at 50 degrees F., and the fourth at 60 degrees F. Warm to these temperatures before placing mix in freezer. Note swell obtained. Explain.

Fill out record blank on opposite page.

EXERCISE XXVI REPORT

Batch Number   1     2     3     4  
Pounds of Mix        
Gallons of Mix        
Temperature of Mix        
Time of Starting Freezer        
Time of Stopping Freezer        
Temperature of Ice Cream          
Gallons of Ice Cream        
Gallons of Swell        
Per Cent of Swell        
Comments:

EXERCISE NUMBER XXVII
EFFECT OF THE TIME OF FREEZING ON
THE SWELL AND QUALITY OF ICE CREAM

Make enough mix for four 10 gallon batches of ice cream, using the following formula:

  • 40 pounds of 20% cream
  •  8 pounds of sugar
  •  4 ounces of vanilla extract
  •  4 ounces of gelatin in 4 pounds water.

Freeze the first batch as a preliminary one. Regulate either the temperature or quantity of brine so that the second batch will freeze in four minutes, the third in fifteen minutes, and the fourth in thirty minutes.

Note particularly the effect on the swell and quality.

Fill out the record blank on opposite page.

EXERCISE XXVII REPORT

Batch Number   1     2     3     4  
Pounds of Mix        
Gallons of Mix        
Temperature of Mix        
Time of Starting Freezer        
Time of Stopping Freezer        
Temperature of Ice Cream          
Gallons of Ice Cream        
Gallons of Swell        
Per Cent of Swell        
Comments:

EXERCISE NUMBER XXVIII
BACTERIAL COUNTS OF ICE CREAM

This exercise is to be performed once during the course by each student as assigned.

Sterile glassware and media will be furnished you. Weigh or measure the samples for dilution as instructed.

Take samples as indicated below in sterile bottles and plate on plain lactose agar. Incubate at 37 degrees C., for 48 hours.

  • Sample of cream. Dilutions ¹/₁₀,₀₀₀ and ¹/₁₀₀,₀₀₀.
  • Sample of gelatin. Dilutions ¹/₁₀ and ¹/₁₀₀.
  • Sample of vanilla. Dilutions ¹/₁₀.
  • Sample of sugar. Dilutions ¹/₁₀.
  • Sample of mix. Dilutions ¹/₁₀,₀₀₀ and ¹/₁₀₀,₀₀₀.
  • Sample of ice cream from freezer. Dilutions ¹/₁₀,₀₀₀ and ¹/₁₀₀,₀₀₀.
  • Sample of ice cream after it has remained in the hardening room
  • one week. Make dilutions of ¹/₁₀,₀₀₀ and ¹/₁₀₀,₀₀₀.

Report results on the blank page opposite.

EXERCISE XXVIII REPORT

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