If quinces are colourless, why is quince paste red?

quinces If quinces are colourless, why is quince paste red?

Have you ever seen these ugly looking fruit? It is autumn here in Melbourne and I came across some of them at a local farmers market last weekend. They are called quinces and they are like a cross between an apple and a pear. Straight off the tree they are practically inedible. However with some cooking and chemology they become a delightful addition to your kitchen. So what is it that makes quince paste red?

The chemology part

There are hundreds of molecules that are responsible to the colour of plants, fruits and vegetables, such as chlorophyll which is what makes leaves green. There are a group of common pigments responsible for most of the red, purple and blue colours of plants, including tomatoes, strawberries, apples, potatoes and cabbage. This group of compounds are called anthocyanins, from the Greek “antho” meaning flower and “cyan” meaning blue. You might think that not too many fruit in nature is blue. But many of these compounds are red in acidic environments (like lemon juice) and blue in alkaline environments (did you ever do the red cabbage indicator experiment when you were a kid?).

So… what about the quinces? They’re not red, they’re colourless. That is a quirk of nature to protect the fruit from hungry animals. There are lots of anthocyanins in quinces, they are just all bound up together in big molecules called tannins. The tannins make the fruit unpalatable. To make the fruit edible, the tannins need to be broken down into smaller parts and to do that you need heat or acidic conditions. Once you heat up the colourless tannins, the coloured anthocyanin pigments are released.

How the chemology affects texture – quinces are really hard

Quinces are gritty, astringent, and hard even when ripe. The bitter astringency is as a result of the tannins. You may be familiar with the feeling of astringency in your mouth. It is the same feeling you get when you drink a red wine that is rich in tannins. It is a tactile sensation, a dry, puckery, rough feeling. The sensation of astringency is caused when tannins bond to proteins in our saliva, which normally provide lubrication and help food particles slide smoothly along the mouth surfaces. Tannins cause the proteins to clump together and stick to particles and surfaces, increasing the friction between them.

The tannins in the quinces are destroyed when cooked, while the delicate rich flowery aroma of a raw quince is maintained, turning the hard, tannic, astringent fruit into a softened and milder flavoured fruit.

How the chemology affects colour – the transformation to make quince paste red

Like I said above anthocyanins are pigments responsible for the colours of plants. However, when they are tied up as tannins the fruit has no colour. That is why the pureed quinces are yellow when we start cooking.

Usually cooking is an enemy of colour, but this is one of the few occasions that cooking actually creates colour, because the heat breaks down the bonds between the pigment units in the tannins. Not only does cooking release pigments, but the addition of lemon juice created a little acidity helps the colour compounds to stabilise. The result is the light yellow quinces become a deep ruby colour, due to the red colour of the released pigments.

quincepaste If quinces are colourless, why is quince paste red?
Do it yourself

So now you know how to make quinces edible, you can do it yourself. All you need is some quinces, time, heat and probably acid. You could make poached quinces, quince jelly, Ayva tatlisi or quince paste. Quinces have a high level of pectin and are therefore particularly good in preserves. I have a cheese and a Spanish obsession, so I made the Spanish version of quince paste, which is called membrillo. Here is a recipe for you to do it yourself at home:

Membrillo (Quince Paste)

Cook Time: 4 hours

Yield: around 1.5L

Ingredients

  • 3 quinces
  • 1/2 vanilla pod, split
  • peeled rind of 1 lemon
  • about 5 cups sugar
  • about 5 tsp lemon juice

Method

  1. Wash your quinces thoroughly to remove all white fuzz. Quarter and core (no need to peel). Place into a large saucepan and cover with water. Add the lemon peel and vanilla been.
  2. Boil for 30-60 minutes, or until the quince are fork-tender.
  3. Remove from heat and strain (You can reserve the liquid for another purpose if desired. It is full of flavour and pectin). Remove the vanilla pod.
  4. Use a food mill or stick blender to puree the cooked quince.
  5. Use cups to measure the purred quince as you return it to a large pot. Add the same volume of sugar to the puree (I had about 5 cups). Scrape out the seeds of the vanilla pod and add to the puree. Add one teaspoon of lemon for each cup of puree. Mix well.
  6. Place on medium heat, cover and simmer for 2-3 hours, stirring frequently to keep it from burning (I highly recommend using a splatter guard or a sheet of foil poked with a spoon hole to stir. I found quince paste on my wall over 5 metres away from the splatter!). The paste will be ready when it has thickened and turned a dark red colour.
  7. Line a baking dish with baking paper. Pour the paste into the dish and smooth the top.
  8. Refrigerate overnight. Cut into squares. Store by wrapping in paper and plastic wrap. It will keep for 6-12 months in the refrigerator.
  9. Serve with Manchego cheese.
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 If quinces are colourless, why is quince paste red?

Resources:

Harold McGee On Food and Cooking: The Science and Lore of the Kitchen If quinces are colourless, why is quince paste red? 2004, Scribner, United States.

Nathan Myhrvold, Chris Young &  Maxime Bilet Modernist Cuisine: The Art and Science of Cooking If quinces are colourless, why is quince paste red? 2011, The Cooking Lab, United States.

Simon Quellen Field Culinary Reactions: The Everyday Chemistry of Cooking If quinces are colourless, why is quince paste red? 2012, Chicago Review Press, United States.

Robert L. Wolke, Marlene Parrish What Einstein Told His Cook 2: The Sequel: Further Adventures in Kitchen Science (v. 2) If quinces are colourless, why is quince paste red? 2005, W. W. Norton & Company, United States.

Kate Zuckerman The Sweet Life: Desserts from Chanterelle If quinces are colourless, why is quince paste red? 2006, Hachette Book Group, United States.

Juríková, T. et al. “Flavonoid Profile of Saskatoon Berries (Amelanchier alnifolia Nutt.) and Their Health Promoting Effects” Molecules 2013, 18, 12571-12586, doi:10.3390/molecules181012571

Santos-Buelga, C. & Scalbert, A. “Proanthocyanidins and tannin-like compounds—Nature, occurrence, dietary intake and effects on nutrition and health”  J. Sci. Food Agric. 2000, 80(7), 1094–1117, doi: 10.1002/(SICI)1097-0010(20000515)80:7<1094::AID-JSFA569>3.0.CO;2-1

Hamauzu, Y. & Mizuno, Y. “Non-extractable procyanidins and lignin are important factors in the bile acid binding and radical scavenging properties of cell wall material in some fruits” Plant Foods Hum. Nutr. 2011, 66(1), 70-77. doi: 10.1007/s11130-010-0207-z

Recipe inspiration:

How to make quince paste

Simply Recipes – Membrillo (Quince Paste)