Ripening Green Tomatoes

Friday, September 18, 2009 by Jeremy Dore - Categories: gardening tomatoes
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The very best tasting tomatoes are those that are ‘vine ripened’ – left to reach a deep vibrant colour on the plant.  Nothing beats the taste of freshly picked ripe tomatoes which are, without question, infinitely superior to shop-bought produce.  However, as the season draws on and temperatures start to drop there are invariably lots of green tomatoes left on the plants that don’t quite ripen in time.  Rather than wasting them, why not try some easy techniques to ripen them indoors?

What Makes Tomatoes Ripen?

Contrary to popular belief, windowsills are not the best place for ripening up tomatoes.  Take a close look at your tomato plants and you will learn why: surprisingly, tomatoes often start to ripen on the opposite side of the fruit to the sunny side although not all varieties show this.  So, plenty of light is not required for ripening and, in fact, it tends to make the skins of the fruits harder.

Temperature, on the other hand, is a very important factor.  The warmer a tomato fruit is the quicker it will ripen.  So you can slow down ripening by placing tomatoes in a cool area or speed them up with moderate warmth.

The third factor that speeds up ripening is a gas called ethylene.  This is the gas that is used commercially with tomatoes and other fruits that are picked green before shipping and then ripened for sale.  Although this all sounds very artificial and leads to rather bland-tasting produce, ethylene is actually naturally released by ripening fruits such as bananas, apples and tomatoes.  So, placing a ripe banana or apple in with some green tomatoes in an enclosed space helps to speed up the ripening process.

Different Methods

There are several ways to ripen tomatoes indoors:

1. In a cardboard box:  Line the box with newspaper (or use fruit cardboard if it came from a grocery store) and place the green tomatoes on top in a single layer with a little space between each.  Cover with another single layer of newspaper and leave somewhere warm.  Check regularly.  Another variation of this method is to place the tomatoes in a wooden drawer although you would be lucky to find a spare drawer in my house!
2. In a paper bag: Put 5 -10 tomatoes in a paper bag with a ripening banana, apple or tomato and leave in a warm place.  Periodically open it up to check for any that show signs of mould or rotting.
3. Large glass jars or plastic bags: Another way to concentrate the effect of ethylene involves placing 2-4 large tomatoes in a jar or bag along with a ripening fruit and then sealing it.  However, the combination of moisture and warmth can encourage mould so it is usually best to put holes in the bag or regularly open and check the jar.
4. Hang up the whole plant: Useful at the end of the season when a frost is forecast, the whole tomato plant can be gently pulled up and then hung upside down in a garage or cellar where temperatures will remain above freezing.  This is said to produce better flavoured tomatoes than the other methods.

For each of these methods the best results come from tomatoes that are already starting to show a yellowy-orange tinge indicating that they are ready to ripen.  You can have success with fully green tomatoes but they will take longer and may not be so flavoursome.

At lower temperatures 10-15°C (50-60°F) ripening typically takes 3-4 weeks whereas at 18-21°C (65-70°F) they can take just 2 weeks.  By storing batches at different temperatures you can stagger the ripening to make the most of your harvest although anything much lower than 10°C (50°F) will yield poorer quality results.

What to Watch Out for

The biggest problem when ripening tomatoes indoors is diseased or damaged fruit.  Tomatoes must be protected from being bruised or squashed so they should not be piled up.  Good air circulation will help prevent mould forming.  It is sensible to do a check every day or two, removing anything suspect.

Regular checking is particularly important if you are ripening tomatoes indoors because your plants suffered from a disease such as blight before the crop was ready.  In such cases a useful technique is to ‘grade’ the tomatoes before storing them, separating out unblemished ones from lower quality fruit.  Select only the very best ones for ripening and dispose of any diseased fruit in a safe way.  I have used this technique with some success this year for my own tomatoes that succumbed to blight and found the key was getting them off the plant at the very first sign of the disease.

If you have had success with a particular method of ripening tomatoes, or even have a good recipe for using green ones then please do add a comment below...