Ice cream. Principles of ice cream mix calculation

This article is still being finalised and will be subject to change over the next month or so.

Over the past 18 months or so numerous enquiries about ice cream have been directed to the Dairy Science and Food Technology website. These have been mainly related to ice cream mix calculations and to faults with the final product and are probably a reflection of increasing numbers of people becoming involved in ice cream manufacture.

While some attempt has been made to address queries in the Forum I have decided to include some material on the science and technology of ice cream production. This material will be developed over the coming months and will include contributions from external experts. Because of user interest priority has been given to including information and calculators on ice cream mix formulation.

There is a low cost booklet, ‘Ice Cream Making' by James Rothwell that is recommended to readers interested in this area. This provides a good overview of ice cream generally, deals with the concept of a balanced ice cream mix and explains how to perform ice cream mix calculations. While the booklet was published in 1985 it is still relevant today. Copies are available from the Ice Cream Alliance.

Manufacturers produce ice cream to meet the requirements of consumers as interpreted by the retailers or those selling directly to consumers.

In many situations the ice cream manufacturer will have a final product specification to meet. One element of this specification is related to the composition of the final product including legal requirements e.g. for fat and milk protein. In the UK ice cream must contain a minimum of 5% fat and a minimum of 2.5% milk protein. A compositional specification will typically specify the fat, milk solids not fat (MSNF), sugar, emulsifier and stabiliser concentrations in the final product. In this situation the manufacturer will select ingredients that can supply the above components, blend these and then process to produce a finished ice cream. Calculations will be required to ensure that the ingredients are correctly formulated to meet the final product specification.

In other situations the manufacturer may want to produce a new or improved product and will have to devise their own product compositional specification. This specification must be developed so that the fat, sugar and MSNF components are balanced.

Fat /Sugar balance

Fat adds certain taste and other qualities to food. In ice cream fat is balanced by sugar and there is a relationship between fat concentration and sugar concentration.

The relationship between fat and sugar concentrations is also influenced by the type of freezer used (Table1).

TABLE 1: Approximate fat and sugar contents for ice cream mixes using various types of freezer

Note the fat/sugar ratios here are approximate and that this information does need to be modified to meet consumer requirements. The market has also changed since 1985 and some of the more popular types of dairy ice cream may contain 15 % fat. However, from a product development perspective the information in table 1 provides a good start.

Guinard et al. (1996) studying the influence of fat and sugar in a vanilla ice cream used university students to taste and rate on a nine-point hedonic scale the texture and mouth feel, flavour (taste and odour), and overall degree of liking for nine samples of vanilla ice cream varying in sugar (8.94 to 18.81%, wt/wt) and fat (8.73 to 19.30%, w/w) concentration.

The hedonic ratings differed significantly among samples, and the best-liked sample for texture and mouth feel, flavour, and overall degree of liking contained 13.54 % sugar and 14.99 % fat. Response surface methodology, in simple terms a three dimensional graphical analysis of overall degree of liking versus sugar and fat concentrations, was used to relate hedonic ratings to sugar and fat percentages in the ice cream. Dome-shaped response surfaces,e.g. figure 1, were obtained for all three degree of liking parameters, and optimal sugar and fat, respectively, were 13.16 % and 14.02 % for degree of liking of texture and mouth feel, 14.07 % and 15.35 % for degree of liking of flavour, and 14.30 % and 14.77 % for overall degree of liking.

The results from figure 1 show clearly that particular sugar concentrations are required to obtain maximum overall degree of liking ratings for particular fat concentrations and show the value of this simple research tool.

Some research has been published in the optimal fat and sugar concentrations required for maximum acceptability of ice cream, table 2. Surprisingly, perhaps,there appears to be agreement in that fat concentrations around 14% and sugar concentration of around 15% give the most acceptable ice cream.

TABLE 2. Optimal fat and sugar levels required for maximum acceptability of ice-cream
Country	Fat (% w/w)	Sugar (% w/w)	Reference
Egypt	14	15	*Salam et al* . (1981)**
US	14.3	14.77	*Guinard et al.* (1996)**

Ice cream is a complex colloidal system and includes ice crystals in a concentrated unfrozen aqueous phase. This aqueous phase contains a concentrated lactose solution.

When the MSNF concentration is optimal the ice cream has a smooth body, a characteristic ice cream taste and will have a satisfactory shelf life.

At high MSNF levels the lactose concentration in the unfrozen aqueous phase may be so high that the lactose comes out of solution and that crystals of lactose grow. This may result in ‘sandiness' in the final product.

At low MSNF there is a tendency for the ice cream to taste ‘watery' and to lack characteristic ice-cream flavour. Growth of ice crystals may also be promoted.

Rothwell (1985) has illustrated how to calculate the maximum, note not necessarily the optimal, concentration of MSNF; all the solids apart from MSNF are summed and subtracted from 100. The product is then divided by 7 to give the maximum acceptable value. MSNF absorb about 6 times their own weight of water. As an example a mix containing 8% fat, 13% sugar, 1% stabiliser/emulsifier should have a maximum MSNF of

Organic ice-cream makers using cream and or butter to raise the fat content of on farm produced ice cream but who do not use skim milk powder or concentrated milk as a source of additional MSNF will find it difficult to meet ideal MSNF recommendations. To some extent the use of organic stabilisers can help overcome some of the problems that can arise with low MSNF ice cream during storage.

There are several methods that can be used to determine the quantities of ingredients required to meet a target ice cream mix formulation. However, ingredient costs are also important and there is a balance between cost and quality that often must be considered. One of the simpler methods for performing mix calculations is known as the serum point method and can be learned quite quickly. Mixes compositions can also be calculated using linear programming and other more advanced mathematical techniques.

Descriptions of this method can be found in several text books including Hyde and Rothwell (1973) and Marshall and Arbuckle (2000). While these books use the older imperial measures e.g. pounds they are easy to follow. A particularly clearly written explanation, for a limited number of mixes, is given in the booklet by Rothwell (1985). Professor Douglas Goff, University of Guelph in Canada has an excellent website dealing with ice cream and has a section on worked examples of mix calculations.

The serum point method is based on the principle that the quantities of MSNF and fat contributed by ‘milk' of any composition can be subtracted from the entire quantity of fat and MSNF required in a mix, leaving the remainder to be supplied by concentrated sources of MSNF or fat.

There is a logical approach to solving problems using this method and the following description has been adapted from that given by Marshall and Arbuckle (2000).

1. List the fat, MSNF, sugar, emulsifier, and stabiliser concentrations, usually as percentages, that are required in the ice cream mix.

2. The quantities of single source ingredients required for 100 kg of mix are then calculated next. For example if 15 % sugar is required, then:

3. Next the weight of serum in the mix (serum is water and MSNF or milk serum solids) and is obtained by subtracting the weights of all of the other ingredients from 100 kg of total mix.

• To calculate the quantity of concentrated milk needed, it is necessary to know the quantity of serum solids and the quantity of serum in 1 kg of concentrated milk as well as quantities of the same components in the mix. The formula for the quantity of concentrated milk is

Note the figure 0.09 represents the approximate % MSNF of skim milk and represents 9% MSNF in milk, if the actual value has been determined by analysis then this should be used. Concentrated milk is a general term for milk powder, condensed or evaporated milks and other sources of concentrated milk solids.

5. If the concentrated milk also supplies sugar or fat, these contributions must be calculated:

6. The quantity of fat required in the mix is calculated from the milk and cream, or milk and cream sources, by subtracting the quantity of fat in the concentrated milk from the total quantity of fat needed in the mix:

7. The quantity of sugar that must be added to the mix is calculated by subtracting the quantity of sugar in the concentrated milk from the total quantity needed in the mix:

8. If there is no fat or sugar in the concentrated milk, steps 6 and 7 are not required.

9. The quantity of milk and cream required are calculated by subtracting the total of all other ingredients from the 100 kg of mix:

11. Calculate the quantity of milk needed by subtracting the quantity of cream from the total quantity of milk and cream.

13. The calculations should be verified by preparing a table listing all the ingredients, their weights and their MSNF, fat and sugar contributions. These should be added and compared with target values to ensure that the calculation has been undertaken correctly.

The websites and text books below along with the general instructions above provide a good introduction to the principles of ice-cream mix calculation.

Hyde, K. A. and Rothwell, J. (1973) Ice Cream. Edinburgh , Scotland : Churchill Livingstone.

Marshall, R. T. and Arbuckle, W. S. (2000) Ice Cream. Fifth edition. Gaithersburg , MD , U.S.

Rothwell, J. (1985) Ice cream. Reading University , UK . Published by Dr James Rothwell. Available through the Ice Cream Alliance.

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