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FScN 3102: Custards - Protein Coagulation University of Minnesota

Custards - Protein Coagulation

FScN 3102 Introduction to Food Science

Fall 1996


To determine the influence of heat on thermal coagulation of egg proteins. This will be accomplished by preparing custards with varied heating conditions and egg protein.


milk 237 ml (1 cup)
sugar 25 g
1 egg (48 g)
few grains salt
vanilla 1/4 tsp.


  1. Scald milk in double boiler.
  2. Beat egg slightly (white and yolk should be thoroughly mixed but not foamy.)
  3. Stir sugar and salt gradually into egg.
  4. Pour scalded milk into egg-sugar mixture, stirring constantly.
  5. Add 1/4 tsp. vanilla and stir.
Pour the mixture into two custard cups and cook according to the directions given below for the appropriate treatment. Each formulation makes 2 custards. Your TA will help members of your group decide which treatments to make. Each group should make all treatments.

Preparation of custards.

  1. Oven Control
    1. Preheat oven to 350°F.
    2. Prepare custard mixture as directed above.
    3. Set custard cup in a Pyrex baker as deep as the custard cup.
    4. Fill the baker with hot water to the level of the custard in the cup. Place in oven.
    5. Bake until the tip of a sharp knife inserted halfway between the center and edge of the custard comes out clean. (Approx. 40-50 min.)
    6. Remove immediately from hot water and place on a rack to cool, then evaluate custard.
  2. Oven Variation:
    Into a 350°F oven as in the Oven Control but without doing Step 4. Remove when a knife inserted into the custard comes out clean. Record the baking time.
  3. 2 Egg Variation: (bake in an oven as in Oven Control.)
    Prepare custard according to the basic mixture, using 96 g of whole egg (2 eggs).
  4. Microwave
    Cover the custard cup with plastic wrap. Poke a few holes in the plastic to allow steam to escape. Adjust microwave time and power to get the best product you can.


  1. Quality of custard.
    Continuous clotted mass (gel) firm enough to hold its shape and to hold fairly sharp angles when cut.
    Smooth, homogenous--no porosity or syneresis.
    Delicate--no pronounced egg flavor.
  2. Objective tests.
    1. Percentage sag.
      1. Insert a skewer through the center of the custard and measure the depth of penetration in centimeters. Loosen the custard from the cup with a spatula and turn out on a plate. Immediately,
      2. insert a skewer through the custard at its highest point and measure the depth of penetration as before.

        Percentage Sag = (Reading 1 - Reading 2) / Reading 1 X 100

        Record your percentage sag readings in your lab book and on the class data sheet. We will collect the data from all the classes and you can put it into your lab book.

    2. Syneresis of custard on selected samples (The TA will tell you which samples to measure). Custard that has been used for percentage sag can be used. Invert custard into a funnel partially plugged with cheese cloth and allow to drain for 10 min. Measure volume of liquid. Record the observation in your lab book and on the class data sheet.

Oven Control Oven Variation 2-eggs Microwave
% sag: % sag: % sag: % sag:
% sag from class: % sag from class: % sag from class: % sag from class:
Syneresis volume: Syneresis volume: Syneresis volume: Syneresis volume:

By now you should know how and what to discuss in your lab book. Ask a TA or the instructor If you have questions. Remember that by writing in your lab book you show yourself and others that you understand what you and others did in the lab and why the different treatments produced different products. This practice of writing about the material you are learning should pay off in better scores on exams, better retention of all you are learning and better lab notebook grades!

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© 1996 by the Regents of the University of Minnesota.
The Department of Food Science and Nutrition.
All Rights Reserved.

Last Modified - 8/7/96