MISS: SALSABEEL H. AL JOUJOU

Objectives-:Be able to produce of yoghurt using Lactobacillus delbrueckii and Streptococcus thermophilus.

I. Introduction:-

Yoghurt or yogurt, less commonly yoghourt, joghurt or yogourt, is a dairy product produced by the controlled fermentation of milk by two species of bacteria (Lactobacillus sp. and Streptococcus sp.).

The sugar in milk (called lactose) is fermented to (lactic acid) and it is this that causes the characteristic curd to form.

I.1 Yogurt Types: 1. Set yogurt: A solid set where the yogurt firms in a container and not disturbed.

2. Stirred yogurt: Yogurt made in a large container then spooned or otherwise dispensed into secondary serving containers.

The consistency of the “set” is broken and the texture is less firm than set yogurt. This is the most popular form of commercial yogurt.

3. Drinking yogurt: Stirred yogurt to which additional milk and flavors are mixed in. Add fruit or fruit syrups to taste.

Mix in milk to achieve the desired thickness. The shelf life of this product is 4-10 days, since the pH is raised by fresh milk addition.

Some whey separation will occur and is natural. Commercial products recommend a thorough shaking before consumption.

4. Fruit yogurt: Fruit, fruit syrups, or pie filling can be added to the yogurt. They are placed on top, on bottom, or stirred into the yogurt

I.2 Health benefit of yogurt 1. Yogurt is easier to digest than milk.2. Yogurt contributes to colon health.3. Yogurt remains an excellent source of calcium.4. Yogurt can boost immunity.5. Yogurt .6. Yogurt can lower LDL ,Raise HDL cholesterol.

II. Method of processing:

II.1 YoghurtThere are two types of plain (unflavored) yoghurt that are produced under control conditions.

These are set that yoghurt that has a firm crud and stirred yoghurt that has a smooth creamy consistency, similar to a thick cream.

The production method is:

1. Heat milk in a stainless steel (or less desirably an aluminum) pan to 80- 85 ºC for 15- 20 min. with constant stirring.

2. Cool 40- 45 ºC as quickly as possible and add a starter culture (or inoculum) of the mixed lactic acid bacteria.

3. Depending on the yoghurt required, the milk is either kept in pan (for stirred yoghurt) or filled into individual retail pots (for set yoghurt).

4. Incubate the milk at 40- 45 ºC for 4- 6 hrs to allow the fermentation to take place.

5. For stirring yoghurt, the pan of the crude is then stirring using a sterilized spoon or ladle until the crude becomes a smooth cream that has a thick consistency without any lumps.

6. Both types of yoghurt are stored in a refrigerator at 4- 8 ºC.

II.2 Flavoured or fruit yoghurtFlavoured or fruit yoghurt is produced the same as plain yoghurt. For flavoured yoghurt, the essence (e.g, vanilla, chocolate or fruit flavour) with or without coloring, is added befor the milk is fermented.

Yoghurt that contains fruit pulp is made in the similar way to plain yoghurt and the fruit pulp is added after fermentation. Less acidic fruits such as melons or pawpaw (papaya) are more successful because they don’t react with the milk. Acidic fruits (lemons, lime, pineapple, etc.) may cause excessive curdling and separation of the yoghurt. 

II.2.1 To make fruit pulp1.Select fully rip fruit.

2.Wash in clean water.

3.Remove the peel and seed.

4.Pulp the fruit.

5.Heat the pulp for 15- 20 min. at 70- 80 ºC in stainless steel pan, with constant stirring to prevent it burning in to the pan.

This softens the fruit and destroys any contaminating microorganisms and naturally occurring enzymes that would cause changes to the color or flavour of the fruit during the storage.

6.Cool to room temperature.

7.Either mix the pulp into stirred yoghurt (e.g. one part pulp between three to five parts yoghurt) or place a layer of pulp at the bottom of pots before filling stirred yoghurt.

8.Store as for plain yoghurt