ICE CREAM PRODUCTION
There has been little tradition of ice cream production in tropical countries because of the requirement for refrigerated production equipment and frozen storage. Now demand is increasing for ice cream in many large t owns and cities, and it has the potential to be a profitable product for small scale dairies. However, ice cream carries a high risk of causing food poisoning if it is not correctly made and stored (see Technical Brief: Overview of Dairy Processing), and it should therefore only be produced by dairies that have knowledgeable and experienced staff. Ice cream is made by freezing and simultaneously beating air into (aerating) a liquid mixture that contains fat, sugar, milk solids, an emulsifying agent, flavou ring and sometimes colouring. The fat can be from milk, cream or butter or from a non -dairy source. However, the composition of ice cream is legally defined in many countries. Typically this is: 1. Standard ice cream that contains not less than 5% fat and not less than 2.5% milk protein (from casein or whey solids). 2. ‘Dairy’ ice cream must contain a minimum of 5% fat that is only milk fat and not any other type of fat. There may also be legislation that covers the types of emulsifying agents, colourings, fl avourings or other additives that are permitted in ice cream, and potential producers should check the local legislation at a Bureau of Standards before formulating a product. Ingredient Full cream milk Liquid skim milk Full cream milk powder Skim milk powder Double cream Single cream Butter Sweetened condensed milk Evaporated milk Fat (%) 4.0 27.0 48.0 18.0 84.0 9.0 9.0 MSNF1 (%) 8.8 9.0 70.0 97.0 4.5 7.2 22.0 22.0 Sugar (%) Water (%) 87.2 86.0 3.0 3.0 47.5 74.8 16.0 25.0 69.0
Table 1: Typical composition of ice cream ingredients (From Opportunities in Dairy Processing).
MSNF = milk solids not fat
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Product variations There are a large number of potential product variations, including a wide range of flavours (e.g. vanilla, chocolate or fruit flavours) and corresponding colours, and different textures that depend on the addition of additives or differences in the method of production. Fruit pulp may also be added during or after making ice cream, and fruit, chocolate or nut pieces ca n be used to decorate ice cream. In temperate climates, ice milk was the traditional lower -fat ice cream product, and in places where there is a demand for reduced -fat products (with fat contents as low as 4%) this may be an additional product in a range. Another product variation is frozen yoghurt (see Technical Brief: Soured milk and yoghurt production), which is frozen in a similar way to ice cream (below).
Fats Fats increase the richness of the ice cream flavour, produce a smooth texture, give ‘body’ to the ice cream and produce good melting properties when the ice cream is eaten. Although dairy fats (Table 1) are most commonly used to make ice cream, a number of vegetable fats (including hydrogenated palm oil, coconut oil or salt-free margarine) may be cheaper and are used to reduce the cost of ice cream. Milk solids-not-fat Milk solids-not-fat is included as skimmed milk powder or full-fat milk powder. They improve the body and texture of ice cream, allow a higher overrun (below), and produce a thicker, less icy product. Sugars Sweeteners improve the flavour, texture and palatability of ice cream. They contribute to a lower freezing point, so that the ice cream has some unfrozen water. Without this the ice cream would be too hard to eat. They also reduce the ‘fattiness’ of ice cream and help to produce a smooth texture. Granulated or castor sugar (sucrose) is used, but other sugars (such as dextrose powder) are also used to make the ice cream softer. Corn syrup produces a firmer and ‘chewier’ ice cream than sugar. It is available in different dextrose equivalents1 (DE). The sweetness increases with higher DE values. Lower DE corn syrups have a greater stabilising effect. Stabilisers Stabilisers are used to help bind together the compl ex mixture of fats, sugars, air and tiny ice crystals that are present in ice cream and give a smooth texture. They increase the viscosity in the unfrozen water to produce a firmer ice cream that resists melting (see ‘Product control’ below). Historically gelatine was used, but now the most widely used commercial stabiliser is carboxymethyl cellulose (CMC), which may have small amounts of vegetable gums (such as guar gum or locust bean gum), or seaweed extract (available as sodium alginate) mixed with it to improve its stabilising action. The vegetable gums may also be used instead of CMC. The amounts of stabiliser used should follow the manufacturer’s recommendations. Emulsifiers Emulsifiers create a smooth texture and good melting characteristics. The tra ditional emulsifier used in ice cream was egg yolk, but now mono- and di-glycerides and Polysorbate 80 are used in most ice cream formulations. Flavourings and colourings Few people like unflavoured ice cream and both synthetic and natural flavours are us ed. The colouring normally matches the flavour (e.g. green colour with mint flavour or orange with mango). The flavours and colours must be ‘food grade’ and are usually available in supermarkets in major towns and cities or from bakery ingredient suppliers . Vanilla flavour is often the most
DE is a measure of the reducing sugar content of the syrup calculated as % dextrose
popular flavouring, but producers should find out local preferences before deciding the range of flavours to offer (see for example ice cream makers such as Ben and Jerry’s, makeicecream.com, or flavour suppliers such as H. E. Stringer or other large producers for the range of possible flavours). Formulating an Ice Cream Mix It is important that small producers understand how to develop new ice cream mixes to meet changing customer demands. ‘Balancing’ the mix involves maintaining the correct balance between: Fat and sugar which controls the ‘fattiness’ of the product in the mouth. Water and solids which controls the texture or hardness/softness. The formulation of an ice cream mix should also take into account the cost and availability of ingredients. Details of the method used to calculate the weights of each ingredient in a recipe are beyond the scope of this Technical Brief, but details are given in Dairy Science and Technology Education and ice cream recipes are available at http://makeicecream.com and www.ice-cream-recipes.com. Examples of ice cream mixes are shown in table 2. Low-fat ice Soft-frozen ice creams creams Standard brands Component (%) (%) Fat 3.0 - 8.0 10.0 - 10.0 Milk Solids-not- 13.0 - 11.5 12.5 - 12.0 fat Sucrose 11.0 - 12 13.0 - 10.0 CSS 6.0 - 4.0 4.0 - 4.0 Stabilizer 0.35 - 0.15 0.35 - 0.15 Emulsifier 0.15 - 0.10 0.15 - 0.15 Water 66.3 - 63.7 64.0 - 63.7 Total Solids 33.6 - 36.3 36.0 - 36.3 Table 2: Mixes for ice creams (Adapted from: (%) 10.0 - 12.0 11.0 - 9.5 10.0 - 15.0 5.0 - 3.0 0.35 - 0.15 0.15 - 0.10 64.0 36.0 Hard ice creams Premium brands (%) 12.0 - 15.0 11.0 - 9.5 10.0 5.0 0.35 0.15 62.0 38.0 15.0 3.0 0.15 0.10 60.0 40.0 Superpremium brands (%) 15.0 - 18.0 11.0 - 9.5
10.0 - 15.0 5.0 - 3.0 0.35 - 0.15 0.15 - 0.10 <60.0 >40.0 Dairy Science and Technology Education)
The general method for producing ice cream is shown in Figure 1. The increase in volume of ice cream due to the incorporation of air is known as the ‘% overrun’, and in commercially produced ice creams this varies from 60 -100% or more. In some countries there is a legal maximum of 120% overrun. Overrun % can be calculated as follows: Overrun % = 100 x weight of a given volume of mix – weight of same volume of ice cream weight of same volume of ice cream If, for example, 3.1 kg of ingredient mixture is needed to fill a container so that it is le vel with the top of the container and then with 1.6 kg of ice cream, again level with the top, the % overrun = 100 x (3.1 – 1.6) 1.6 = 100 x 1.5/1.6 = 93.75% Because ice cream is sold by volume, the amount of air in the finished produc t has an important effect on profitability. Small batch freezers (below) can only beat small amounts of air into the mixture as it freezes, to give an overrun of 50% or less. Commercial freezers are more efficient at incorporating air and overruns can be 1 00% or more.
Stage in process Weigh
Notes Premix dry ingredients with 3 or 4 times their weight of sugar. Weigh all main ingredients, except fat, into pasteurisation vessel. To 50 C and add any solid fats. At 65°C for 30 minutes or 72°C for 10 minutes with thorough mixing. For a minimum of 4 hours at 3-5 C to allow fats to crystallise and the viscosity to increase. Using an ice cream machine to reduce the temperature to –5°C as quickly as possible. Fill into pots or cardboard cartons.
Heat Pasteurise Cool Freeze and aerate Pack
Harden At below -20 C Cold store At –18 to -20 C Figure 1: Method of ice cream production
Pasteuriser A pasteuriser is used to heat the ice cream mixture. At a micro -scale of production, a stainless steel pan (or less desirably an aluminium pan) is heated with constant stirring to prevent the mixture overheating or burning at the base of the pan. At small - and medium-scale production, a jacketed stainless steel pan (see Technical Brief Pasteurised milk) gives better control over heating. Steam from a boiler heats the space between the outer jacket and inner pan to give more uniform heating and avoid localised burning of the product. It may be fitted with an agitator. Ice Cream Freezers Small manual or electric ice cream makers have a stainless steel bowl that is frozen by one of three methods: the bowl is immersed in a freezing liquid (e.g. an ice/salt mixture). a double-walled bowl is placed in a freezer, and the salt/ice between the bowl walls is frozen (the bowl needs to be refrozen for the next batch). Typically, both can freeze ice cream within 15 - 20 minutes. the bowl is surrounded by refrigeration coils that are built into the machine (Fig ure 2). Some machines also have a built-in pasteuriser. Other designs (Figure 3) pump the ice cream mixture to freeze and aerate it. These types of machines can produce ice cream continuously and may be used in retail outlets. Each type of ice cream maker has a rotor that scrapes the frozen ice cream mixture from the bowl wall and at the same time incorporates air. Freezing continues until the liquid is frozen at 4 to -7°C. This soft ice cream is then either sold directly or hardened in a freezer at –18°C. At a larger scale, more expensive continuous freezers that have capacities above 200 litres per hour are used.
Figure 2: Small ice cream maker
(Courtesy of Musso ice cream machines)
Figure 3: Commercial ice cream maker
(Courtesy of Robot Coupe)
The quality and amounts of dairy ingredients and the processing conditions that are used for making ice cream should be standardised so that consistent quality products are made each time. This involves control of factors in the process that affect the quality or safe ty of the product. These are known as ‘control points’ and are the points at which checks and measurements should be made (Table 3). HACCP2 The specific potential hazards in making ice cream are food poisoning bacteria from the dairy ingredients, poor hygiene and sanitation during processing, and incorrect processing conditions. Other hazards that are common to all types of food processing (including contamination of foods by insects, glass etc.) are prevented by correct quality assurance, including the d esign and operation of the processing facilities, staff training in hygiene and production methods, and correct cleaning and maintenance procedures. Hygiene Technical Brief: Dairy Processing - An Overview gives details of hygiene and sanitation, the design of a dairy and the use of correct cleaning procedures. Hygiene requirements are also described in Technical Brief: Hygiene and Safety Rules in Food Processing. Avoiding food poisoning Unclean equipment, contaminated ingredients, poor hygiene of production staff, and incorrect processing and storage conditions can each lead to bacteria contam inating the ice cream. Although the low temperatures during frozen storage prevent the bacteria from growing, they can cause illness when the ice cream is eaten. All equipment should be thoroughly cleaned after use and checked before production starts again. The temperature and time of heating the ingredient mixture should be monitored and controlled to ensure that it is not over - or under-heated.
Hazard Analysis Critical Control Point
By Peter Fellows, Published by Practical Action on 02/02/02
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