Jamming session

UNDERSTANDING YOUR FOOD<br /> the ultimate educational resource<br /> TEACHER NOTES<br /> <br /> teachers’ notes G1.1<br /> G1. A jamming session<br /> The initial investigation, which finds out which conditions are necessary<br /> for gel formation using liquidpectin, is suitable for both science and<br /> food technology. There are then further investigations; one for science<br /> and the other for food technology.<br /> Hints for the teacher<br /> • The quantities of substances and times specified are very important.<br /> • The commercial pectin is, itself, quite a viscous liquid and this<br /> must be measured into the tubes bymassrather than volume. For<br /> the initial investigation it may be better to have the pectin already<br /> added to the tubes ready for pupils to use.<br /> • A small amount of citric acid powder, no more than 0.2 g, is all that is<br /> needed. Collect a small amount on the end of a spatula, or similar, and<br /> tap into the appropriate tubes. The contents of the two tubes that<br /> contain sugar should be stirred when the sugar is added and every<br /> minute during heating. This helps the sugar to dissolve and therefore<br /> prevents its accumulation at the bottom of the tube. The stirring rods<br /> should be removed during the cooling period.<br /> The method suggested for comparing the tubes after cooling is very<br /> simple and qualitative. At this point in the investigation it is all that is<br /> needed. The pupils compare viscosity of the liquids in the tubes by laying<br /> the tubes flat. 5 minutes is long enough to see an obvious difference<br /> between tubes C and E. The pupils will find:<br /> • That the liquid in tube E is most viscous; a gel is produced in the given<br /> setting time. None of the others produce the same set.<br /> • Tube C will be more viscous than A, B or D, which will all be very<br /> similar.<br /> This investigation demonstrates to pupils that pectin, to be able to<br /> produce a set, requires:<br /> • heating<br /> • an acidic pH<br /> • and sugar.<br /> Further investigations<br /> In science- the conditions needed for gel formation can all be used as<br /> continuous variables for a Sc1 investigation. However, since the amount of<br /> citric acid required is so small, it would not be particularly easy to<br /> investigate this variable. The others are much easier to investigate, (see<br /> margin). Whichever variable is chosen there should then be evidence of<br /> fair testing by keeping the other variables constant. There is also the need<br /> for pupils to devise a quantitative method of comparing the results; for<br /> example, liquid flow could be carried out against a graduated scale and<br /> timed; the contents of the tubes could be poured into a suitable container<br /> and the area of ‘spread’, in a particular time, measured.<br /> In food technology- here, there is opportunity for jam making<br /> investigations.<br /> Groups could make small quantities of jam using different methods of<br /> producing a set and then compare the jams (see margin box).<br /> Different groups produce jams using different methods and then devise<br /> methods of comparing the jams with respect to setting properties, taste,<br /> colour and keeping qualities.<br /> KS3/4<br /> science and food technology<br /> Timing - 30 - 40 minutes<br /> Pupil activity sheet G1 accompanies<br /> this activity.<br /> Requirements (per group)<br /> • safety goggles<br /> • <25 cm<br /> 3commercial* pectin<br /> solution<br /> • 7 g ordinary sugar (sucrose)<br /> • 5 test tubes/boiling tubes<br /> • test tube racks<br /> • 2 stirring rods<br /> • tiny amount of citric acid powder<br /> • 2 water baths (beakers); 1 boiling,<br /> 1 cold<br /> • Bunsen burner, tripod, gauze,<br /> heat resistant board<br /> • stopclock<br /> * Certo produced by Citrus<br /> Colloids, can be purchased from<br /> supermarkets and is a type of<br /> pectin which would be used to<br /> produce jam and marmalade in<br /> the home.<br /> Allow 15 minutes - to perform a<br /> number of tests and repeats<br /> Variables to investigate:<br /> • amount of pectin<br /> • amount of sugar<br /> • length of heating at a<br /> particular temperature<br /> • different temperatures but same<br /> length of heating.<br /> <br /> teachers’ notes G1.2<br /> Fruit such as strawberries,<br /> raspberries and cherries have low<br /> amounts of pectin and a high pH so<br /> that making jam from these fruits is<br /> more difficult.<br /> There are two main ways of<br /> overcoming these problems:<br /> • often small quantities of other<br /> fruits which are high in pectin and<br /> acid are added to supplement<br /> that in the original fruit.<br /> • alternatively, commercial pectin,<br /> and sometimes lemon juice, can<br /> be used.<br /> This activity could include work on producing jams using artificial<br /> sweeteners, as yet another comparison, which would lead to a discussion<br /> of the preserving properties of sugar that artificial sweeteners fail to have.<br /> It is advised that jams produced using artificial sweeteners are stored in the<br /> refrigerator to slow down microbial, particularly fungal, growth. Pupils<br /> could compare the keeping qualities of ordinary jams and jams made<br /> using artificial sweeteners under normal usage, e.g. opening lids,<br /> removing jam, returning the lid, etc.<br /> Additionally, the production of small quantities of jam at home could be<br /> compared to the commercial production of jam on a large scale (see G2<br /> An introduction to pectin).<br /> Cell wall (cellulose)<br /> Middle lamella<br /> <br /> pupil activity G1 A JAMMING SESSION<br /> The production of jams is a very old and traditional method of preserving fruit. At the<br /> end of summer there is a large quantity of surplus fruit and vegetables that must not<br /> be wasted.<br /> Jams and marmalade are made by boiling the fruit with water and sugar. On cooling<br /> the jam or marmalade will set. This is due to a special group of carbohydrates called<br /> pectins. In the correct conditions, pectin will produce agel. Some fruits, e.g. apples,<br /> blackcurrants, contain a large amount of pectin. They can easily be turned into jam.<br /> Other fruits, e.g. strawberries, raspberries, have a low amount of pectin and need help<br /> to be turned into jam.<br /> In this investigation you are going to find the conditions needed for pectin to produce<br /> a gel and, hence, the conditions needed for making jam.<br /> SAFETY NOTE<br /> REMEMBER TO WEAR GOGGLES<br /> Method<br /> It is very important that you measure the substances accurately.<br /> You must also time accurately the different parts of this investigation.<br /> 1.Label five test tubes A - E.<br /> 2.Add 4 g of commercially produced pectin to each of the tubes.<br /> 3.Heat a beaker of water to use as a water bath.<br /> 4.Treat the tubes as follows:<br /> Tube A - leave as a control<br /> Tube B - no other additions<br /> Tube C - add 3.5 g of sugar<br /> Tube D - add a tiny amount of citric acid powder<br /> Tube E - add 3.5 g of sugar and a tiny amount of citric acid powder<br /> 5.Stir tubes C and E with different stirring rods.<br /> 6. When the water bath is boiling, place tubes B, C, D and E into it for 5 minutes.<br /> You will need to stir tubes C and E every now and then.<br /> 7.After 5 minutes remove the tubes and place them in a cold water bath to cool<br /> them down. Take out the stirring rods. Leave the tubes to cool for 5 minutes.<br /> Results<br /> You now need to compare the contents of the tubes to estimate how thick or viscous<br /> the liquid is and whether or not a gel is forming.<br /> A simple way of doing this is to tilt the tubes and see how fast the liquid travels down<br /> the tube. Make this a fair test.<br /> Write up your investigation. Put the tubes into a rank order by putting the thickest(most<br /> viscous) at the top and the thinnest (least viscous) at the bottom.<br /> What conditions are needed for pectin to be able to produce a set?