Boiling dumplings

UNDERSTANDING YOUR FOOD<br /> the ultimate educational resource<br /> TEACHER NOTES<br /> <br /> teachers’ notes A2.1<br /> Two pupil activity sheets A2<br /> accompany this activity.<br /> Requirements per group<br /> • safety goggles<br /> • 200 g plain ?our<br /> • <2 g ?nely ground<br /> sodium<br /> hydrogencarbonate (e.g.<br /> commercial baking<br /> powder)<br /> • <2 g ?nely ground monocalcium<br /> phosphate* (acid calcium<br /> phosphate)<br /> (*supplied with book)<br /> • 2 or more 1 dm<br /> 3beakers<br /> • bunsen burner, heat resistant<br /> mat, gauze<br /> • stopclock<br /> • Universal indicator & chart<br /> • ink and sponge (optional)<br /> The taste of sodium<br /> hydrogencarbonate used as the sole<br /> raising agent is soapy and thus its<br /> use is limited to baked products<br /> which have strong ?avours such as<br /> gingerbread and parkin so that the<br /> unpleasant taste is masked.<br /> A2. Boiling dumplings<br /> Pupils do practical activities investigating raising agents.<br /> Hints for the teacher<br /> • The ?rst task is to get the water to boiling point in order to cook the<br /> dumplings. A kettle could be used to bring the water to the boil more<br /> quickly.<br /> • The pupils will have to wait 15 minutes for the dumplings to cook and<br /> so can do other tasks during this time. The order of the tasks in this<br /> section could<br /> be altered to accommodate this.<br /> • If the cut surfaces of the cooked dumplings are brushed over with<br /> an ink- soaked piece of sponge, a texture print can be made.<br /> Typical results (see table)<br /> pH<br /> • The pH of the ?nal dumplings shows that ?our alone is acidic.<br /> • Sodium hydrogencarbonate alone makes the dumpling alkaline<br /> (and would give it a soapy taste).<br /> • The monocalcium phosphate alone makes the dumpling acidic.<br /> • A combination of the two results in a typical acid-alkali (carbonate)<br /> reaction and results in the dumpling being approximately neutral.<br /> Raising properties<br /> • A combination of an acid and alkali is needed to produce an<br /> acceptably risen product as this reaction produces carbon dioxide<br /> which is responsible for making the dumpling rise.<br /> • Sodium hydrogencarbonate alone will make the dumpling rise a<br /> <br /> teachers’ notes A2.2<br /> Pupils may wonder why the acid and alkali are not present in equal<br /> amounts.<br /> They could make a dumpling where this is the case (use 0.60 g of each).<br /> This will produce a slightly alkaline, pale yellow dumpling which has a<br /> softer texture.<br /> In commercial situations the proportions of acid (and acid type) to<br /> alkali vary according to the product, taking into account factors such<br /> as added flavours, waiting time between mixing and baking. Most<br /> usually the proportion of monocalcium phosphate to sodium<br /> hydrogencarbonate is 1.2 : 1.0.<br /> <br /> BOILING DUMPLINGS pupil activity A2<br /> Many foods, particularly those made from a dough, rise when they are cooked.There<br /> are a number of raising agentswhich are used in cooking and some of theminvolve<br /> the reaction between an acid and an alkali.<br /> The following investigation considers the effect of components in some raising agents.<br /> Todo this, you are going to make 4 dumplings using different recipes.<br /> Recipe A<br /> 50 g plain flour only<br /> Recipe B<br /> 50 g plain flour<br /> 0.60 g sodium hydrogencarbonate<br /> Recipe C<br /> 50 g plain flour<br /> 0.72 g monocalcium phosphate (acid calcium phosphate)<br /> Recipe D<br /> 50 g plain flour<br /> 0.60 g sodium hydrogencarbonate<br /> 0.72 g monocalcium phosphate (acid calcium phosphate)<br /> Method<br /> 1.Put about 500 cm<br /> 3<br /> of water into two, 1 dm<br /> 3<br /> beakers and heat to boiling. This<br /> will be used to cook the dumplings.<br /> 2.Meanwhile, mix each of the dumpling mixtures with sufficient water to give a<br /> stiff ball of dough.<br /> 3.Place two of the dough balls into each of the beakers of boiling water for<br /> 15 minutes. Make sure you know which dumpling is which.<br /> 4.Remove the dumplings from the water and allow them to cool for a few<br /> minutes after cooking.<br /> 5.Cut each dumpling in half so that you can see inside. Compare the dumplings in<br /> the following ways:<br />
”Which has the greatest volume? Give the greatest one the value 4, the<br /> next 3, the next 2 and the smallest 1.<br />
”Describe the colour as white, off-white, pale yellow or yellow.<br />
”Describe the texture/structure as closed, medium or open.<br />
”Place three drops of universal indicator on a cut surface of each dumpling.<br /> Wait one minute. Describe what happens in terms of colour and pH number.<br /> 6.Put your results in a suitable table.<br /> Try to explain the differences in the results.<br /> What reaction is taking place in recipe D which makes the dumplings rise?