Wednesday, March 18, 2015

Answer: Is the fruit getting sweeter?

This week's question by Miguel Viterbo asked: 

We've heard rumors that farmers add sugar (or some kind of sweetener) to the irrigation of fruit. 
(1) Is this true? Does this actually work to make fruit sweeter? 

 (2) Should I be concerned?  Sugar is already hiding in so many everyday "non-sugar" foods (way more in the US than in Portugal, granted) that I don't want to take any more added sugar.  If it's really more sugar, how much more is it?  

When I first read this question, I immediately thought this sounds like an "urban legend" that could have some basis in fact.  How can we find out?  

Let's chat about strategy for a minute:  

I'd try a couple of different steps to answering this question.  I sat back for a second and thought about what I'm going to do.  Here's what I came up with... 

A.  First, check-assumptions about the question:  Maybe the presumption that "fruits have been getting sweeter over the past decade isn't true.  Is it?  

B.  Second, try a "first principles" approach:  If it's true that fruit is getting sweeter, then I'm going to do a back-of-the-envelope calculation to see if just adding sugar to an irrigation system makes sense.  How many pounds of sugar would you have to feed to a plant to make the fruit sweeter?  How would you dissolve it into the irrigation supply? 

C.  The simple approach:  Search on things like [ irrigation additives ] and explore how people decide what to add to irrigation systems.  I already know they add certain kinds of fertilizers, could they add something that acts to make fruit sweeter?    (Note here--I'm not assuming they're adding just sugar--it could be some kind of artificial sweetener or chemical that acts to increase total fruit sugars.)   In the process, I'm probably going to check out some agricultural schools to see what they teach farmers to put into irrigation systems, and I'm going to look at both row irrigation (where the water flows freely down channels through the fields) and drip irrigation systems (where a small water line is run directly to the base of each plant).  

Start here:  A.  First, check-assumptions about the question:   Let's begin with our assumptions.  HAS fruit been getting sweeter over the past 10 or 20 years? I started with the simple and obvious query: 

     [ fruit getting sweeter over time ] 

This is a long query--why did I add "over time"?  I added that to see if I could get articles that discuss the changes in fruit sweetness, and I would expect that phrase to appear in the text.  

I explored this for a while, finding a couple of articles, e.g., "Sugar high: Why your food is getting sweeter"  which includes the tidbit that a Cornell apple specialist denies that apples are getting sweeter over time, although a Times of London article (requires subscription) claims that food scientists are breeding fruits and vegetables to be sweeter, so our baseline understanding of what’s “naturally” sweet is changing. 

While I read a lot of articles here, all of them suggested that new, and improved varieties are probably making some fruits sweeter.  But, interestingly, none of the articles mentioned changes in irrigation practices.  

So it seems that some fruits have been getting sweeter, but so far, it seems to be slow changes over time with changes in new fruit varieties.  

Let's try our second approach... 

B. Try a "first principles" approach: Would adding sugar to irrigation water work to make the fruit sweeter?  

Let's consider oranges.  How many pounds of fruit will a single tree generate in a year?  

     [ pounds of fruit can an orange tree produce ] 

Which leads to multiple articles, the best of  which is from Texas A&M agriculture school.  "Home fruit production: Oranges" which has a good table of orange tree production as the tree ages.  At maximum production, a single Navel orange tree can produce around 100 pounds of fruit per year. 

Okay.. how much irrigation water will that tree need during the year?  My query: 

     [ how much water does an orange tree need per year ] 

leads to several articles, the best of which is from the University of Arizona agricultural school.  The article, "Irrigating Citrus Trees" tells us that each tree requires a different amount of water, depending on canopy size and the air temperature.  That makes sense... but what's the average?  There's a giant table in that article, when you boil it down, tells us that an average tree needs around 29 gallons / water / day during the growing season.  

If you produce 100 pounds of fruit and want to add sugar to the irrigation water to get a 1% increase in sugar to the fruit, you'll need around 1 pound of sugar to get into the fruit.  If you assume that 10% of the water delivered to the tree is then directed to the fruit, then the irrigation water needs to have 0.29 gallons of sugar, or 5 cups of sugar, to each tree for each day.  (Assuming drip irrigation.)  If you have 1000 trees, that's 5000 cups of sugar to add to your irrigation system each day to keep it at that level.  

1 cup of sugar weighs in at about 0.5 pounds.  So 5000 cups of sugar is around 2500 pounds of sugar each day.  That's a LOT of sugar to be sending out into the irrigation water.  

(And I can easily imagine the troubles with sugar-loving bugs, and problems that sugar-laden drip irrigation lines would cause.  It's seeming less and less probable.)  

C.  The simple approach:  Let's try the simplest query:  

     [ irrigation additives ]   [ irrigation supplements ]   [ "added to" irrigation ] 

Surprisingly, none of these worked especially well. I found lots of off-topic content, but little that led me directly to useful results.  

Now what?  

I know farmers sometimes add things to their irrigation--the question is, what do they call it?  What special terms do they use? 

To find out, I did a search for: 

     [ irrigation fertilizer ] 

and spent a little time reading around on farmer's web site, when I finally found an article on (the US agricultural department).  A ha!  Now I had an entire agricultural site to check out!  (How could I have forgotten them?)  And by reading the farmer articles, I discovered that additives are put into the irrigation system by means of injectors.  (That's the device that adds and mixes irrigation additives to ensure that the contents are mixed and put in at the right time and place.)  

     [ irrigation injector ] 

leads to a LOT of articles--many about pest controls and fertilizer agents.  

And although I tried many queries to follow up on sweetening (or additional sugar) via irrigation and/or injectors, I didn't find anything. 

      [ irrigation sweeten ]    [  irrigation sugar ]  

Not much. 

On the other hand, I DID learn that red-colored plastic film seems to make strawberries sweeter, and that there's a good deal of research to make sugar beets have more sugar.  

But I couldn't find anything about anything added to irrigation to make fruit sweeter.  

A few searches on: 

     [ breeding fruit sweet ] 

led to a large number of articles, many of which point out how active breeding programs have led to sweeter pineapples (such as the "Maui Gold" which is twice as sweet as its predecessor, introduced into Europe in 1996), sweeter strawberries, and sweeter apples.  

So while it's tempting to think that irrigation additives are making the fruit sweeter in taste, the more likely story is that farmers are using the fruits of agriculture breeders in their quest to constantly improve the fruit. 

Whether or not a hyper-sweet apple is to your liking is up to you.  (And there ARE regional preferences in what levels of sweetness and flavor make up a "perfect" apple, orange, or strawberry.)  

But I don't think they're adding anything to the water.... 

Search Lessons:  There are two big ones here.  

1.  Disproving something that's not happening is hard.  As you can tell, a lot of searches that do NOT find anything doesn't definitively close the case, but it does give pretty strong evidence.  The best thing to do here would really be to go talk to an orange farmer, or apple farmer and ASK.  But barring that, a complete sweep of all the different ways you can think of to ask the question.... that's about the best we can do.  Proving that something doesn't exist is always hard. 

2.  When your searches aren't working, look for something in the field that you KNOW you can find; go read there, and learn some language that can help.    That's what I did when I searched for [ irrigation fertilizer ].  I knew that was true.  And in the process of reading broadly in the topic I learned all kinds of terms and concepts that I could use to hone my search more effectively.  

Search on! 

Many thanks again to Miguel Viterbo.  This excellent question comes from him.  


  1. Shouldn't the first thing be to find out if plants can thrive in sugar water?

  2. Great answer!

    I didn't want to confront Isabel, my fruit supplier, before reading the “official” answer in full. I've talked to her today, of how I searched for an answer and where. I summarized it the best I could. Then she rephrased what she had said. In fact, she's never produced fruit nor has she been married to a producer as I thought. So all she knows is what she's being told by the distributors and very few producers that supply her shop. In this process, adding and subtracting here and there, guessing and interpreting this and that, what ends in her knowledge base is a sum of urban myths, tradition and some sparse real technical and technological truth. She believed that sugars were added or something like that.

    In the meantime, I told her about some processes she already had heard of and she told me about one I hadn't heard of (and might probably be only true in part).

    The one process I heard of today:
    Intro. There's a very characteristic Portuguese apple named “Bravo de Esmolfe” which has always been much appreciated but was very rare until less than a dozen years ago. Its production was only around the tiny village of Esmolfe.
    The new process. According to Isabel, this variety of apple takes its pink spots from the following advanced trick: every some trees in a row, farmers nowadays plant some red berry shrub; bees sting the berries then sting the apples and that's how they get their color. Also, she has seen this (I assume she means the berry shrubs among apple trees) near Óbidos (a region famous for their apples too).
    The problem. I had no idea Isabel was so naïve. Apart from the obvious (“stinging” may just be a way of saying extracting nectar and gathering pollen), I very strongly suspect no cross-pollination can occur between different species, or at least between species that distant phylogenetically (apples are in one subfamily, raspberries and strawberries in another one; other berries are way more distant). But there's another pitfall there: this variety of apples is PDO (“Protected Designation of Origin”) and cannot be produced outside its designated area, which does not include Óbidos nor even close (official disclosure brochure here, in Portuguese).
    Isabel may not know that much about fruit after all but she is still my favorite fruit shop owner. She carries excellent and not expensive fruit. She's also helpful and caring with neighbors whenever needed.

    One process I've talked about today: HPP fruit juices (HPP stands for High Pressure Processing; the process is also called HHP, for High Hydrostatic Pressure). She didn't know about it. And I suspect it's not widely known yet, since while I was researching for the fruit sweetness challenge I read at least two articles claiming that in the US, if you read 100% natural on a label, that means it's made from concentrate or it's been pasteurized. Well, I know at least three HPP juice brands in Portugal, all Portuguese, the first one some 8 years old already. Unfortunately, they're expensive.
    For those who don't know these products, let's say it's freshly squeezed juice packed and drank up to one month later still tasting like it was squeezed just now. I'm glad I don't have any interest in any brand, otherwise I could be in trouble just for calling it fresh. Or even raw for the matter.

    After the chat, I bought oranges. I've eaten one now. It was very ripe, extremely juicy and incredibly sweet. It could make me wonder if they're not adding sweeteners to the irrigation.

  3. this summer’s heat waves boosted her crops’ sun exposure and their sweetness too. “The heat causes higher rates of photosynthesis in the peaches which means the sugar levels increase in the fruit,” says High. “Due to the heat, our peaches not only ripened 10 days to two weeks early, but they are extra sweet.”

    check out the rest at