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Sugar level in plant sap at different plants and conditions

Sugar level in plant sap at different plants and conditions

Introduction: (Initial Observation)

All green plants make sugars. A plant’s leaves contain a green substance called chlorophyll (it is this that gives plants their characteristic color). The chlorophyll uses light energy from the sun to combine carbon dioxide and water to produce sugar. The water comes from the soil via the plant’s roots while the carbon dioxide comes in through tiny pores in the plant’s leaves called stomata. The by-product of this process is oxygen.

carbon dioxide + water ——–> oxygen + sugars

The term used to describe the process by which plants make sugar is photosynthesis. It comes from the Greek words ‘photo’ (light) and ‘synthesis’ (joining).

The amount of sugar in plants depends on many different factors. The most important factor is plant type. That is why certain plants such as sugar cane and sugar beet are planted just for producing sugar. In this project we will study the amount of sugar in different plants and different conditions. There are many different types of plants and many different conditions (light, temperature, amount of water, ..) that you may select for your study.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about photosynthesis and sugar production by plants. Read books, magazines or ask professionals who might know in order to learn about the factors that may affect the amount of sugar in plant sap. Keep track of where you got your information from. Following are some of the information that you need.

Plants produce the sugars sucrose, glucose and fructose, these are then stored in the plant. These sugars give fruits their distinctive sweet taste. Sucrose is the sugar most commonly extracted from plants by man.

Sugar beet and sugar cane are the only plants used in the processing of table sugar as it is only these plants that produce and store a sufficient quantity of sucrose.

The Family of Sugars

There are a whole range of substances which make up the family of sugars. These include the sugars made by plants during photosynthesis, milk sugars and honey. Our bodies use all sugars in basically the same way, whatever the source, to give us energy for life.

Sugar Source of sugar
Glucose fruit, vegetables, honey
Maltose barley
Sucrose sugar beet, sugar cane, fruits
Lactose milk
Fructose fruits, honey

Sugars: The Building Blocks for Plants

The sugars produced by photosynthesis provide an immediate source of energy for plants to live and grow. Sugars are also used as the building blocks of complex structures within the plant. For example, cellulose (dietary fibre) forms plant cell walls and provides the plant with structure and support.

Sugars can be stored as starch, which provides an energy reserve at night, when plants are unable to photosynthesise (because of a lack of sunlight).

Starch is also used as a compact energy source in seeds. The young seedlings are unable to photosynthesis and instead rely on this source of energy for growth. Starch is found in large quantities in potatoes, rice and cereal grains (eg wheat).

How to extract sap?

Maple tree is one of the plants that it’s sap is being extracted for it’s sugar content. To extract the sap from maple tree, a tap hole is drilled on the side of the tree.

When drilling the tap hole, regardless of the tool, the hole should be drilled no more than 2.5 – 3 inches beyond the bark. Most maple producers use a drill bit that is 7/16 inches in diameter, and maple supplies are standardized for these sizes of holes. Hole are drilled at an upward slant of about 10 degrees. A sharp drill bit is important to reduce damage to the tree and to drill holes more efficiently.

You may also extract sap from smaller plants such as Broccoli, Brussels Sprouts, cabbage and celery with simpler methods:

1. Get your samples from live plants. See the chart below for the plant part to sample for each crop type.

Broccoli Whole petioles (leaf stem) of youngest fully expanded leaf
Brussels Sprouts Mid-rib of youngest fully expanded leaf
Cabbage Mid-rib of wrapper leaf
Cauliflower Mid-rib of youngest fully expanded leaf
Celery Portion below first node of recently expanded leaf
Lettuce Mid-rib of youngest fully expanded leaf
Spinach Petiole of youngest mature leaf
Onion Roots (washed with water and hand dried)

2. Avoid moisture loss from the tissue samples by keeping them in plastic bags on ice until you are ready for the test. Samples can be stored on ice for 6-8 hours without significantly affecting sugar concentration.

3. Extract the sap from the selected plant part using a garlic press or plant press. Use the same amount of pressure to extract the sap from each sample. For best results and getting a reliable result, you should have 5 to 20 samples of each plant you are testing. Mix all sap samples of each plant in a clean container and allow the sap to come to room temperature before analyzing. Method of extraction must not include grinding and breaking the plant cells.

4. Samples may need to be diluted with distilled water.

Selecting Sugar Maple for High Sap Sugar Concentration

For years maple producers have observed that sap flow and sap sugar concentration vary from year to year, from tree to tree, and from one sugarbush to another. When collecting sap from buckets, maple producers have noticed trees with buckets that overflow during each collection period. Or they may notice trees whose sap requires less boiling time.

These observations can make an important contribution to the Cornell Sugar Maple Tree Improvement Program. The goal of this program is to identify healthy sugar maple trees with higher than average sap sugar content. Trees with these characteristics are currently being propagated on an experimental basis at the Cornell Uihlein Sugar Maple Field Station in Lake Placid, NY. Eventually, the best trees will become part of a larger-scale breeding program, through which landowners will be able to purchase improved sugar maple seedlings for planting in their sugarbush or on abandoned agricultural land.

Maple producers can become part of the Cornell Sugar Maple Tree Improvement Program by identifying and testing trees for high sap sugar content. Trees that express sap sugar concentration at a level well above that of adjacent trees may be selected for the tree improvement program. Twigs will be collected from the superior trees and used to propagate them.

School classrooms, 4-H, and other youth groups that have access to a sugarbush may also want to participate in the effort to identify new, high sugar trees. They may do this in their own sugarbush or in cooperation with a maple producer or other landowner. Even if youth groups are not able to carry out the entire procedure outlined below for testing trees, they can measure sugar content of sap in several trees as an educational experience.

It will be easier to participate in the program if you are tapping with buckets, because this allows you to become familiar with the characteristics of individual trees. However, if you remember outstanding trees from before you switched to tubing, or just want to test the sugar content of individual trees by temporarily removing the tubing, you can also participate in the effort to identify healthy, high sap sugar maple trees.

Trees that produce large volumes of sap may not necessarily have high sap sugar concentration. Also, sap sugar concentration of any one tree varies during the sap flow season and from one year to the next. However, an individual tree with higher sugar content than neighboring trees one year will have higher sugar content than neighboring trees in following years. Therefore, a tree with sap sugar concentration higher than that of nearby trees is of interest to the Cornell Sugar Maple Tree Improvement Program as a potentially, genetically superior tree. Along with increased sap sugar concentration, a tree selected for the program should be of good form and free of defects, evidence of damage from insects and disease, and other factors that could influence sap sugar concentration.

The Tree Comparison Method

The Comparison Tree Method (also referred to as the Five-Tree Tester Method) is used to identify trees with higher than average sap content. Follow the steps below to use the Comparison Method to identify high sap sugar trees.

  1. Select as many trees as possible to test for sugar content.
    The larger the number of trees that can be tested per location, the higher the potential for identifying candidate trees. We have found that out of 100 trees, we might be able to identify two candidate trees.
  2. Keep as many factors constant as possible.
    Factors such as slope, aspect, contour, and microsite are possible sources of variation and should be kept constant.
  3. Keep tapholes uniform.
    Drill tapholes at the same relative location (height and compass orientation) on all trees. If you are going to test immediately after drilling, drill all tapholes within a one or two hour time period. Drill tapholes as close to the beginning of the spring sap flow as possible. If trees are tapped too late, early sap flows may be missed; if they are tapped too early, the taphole may “dry out” before the season ends. If the tree is tapped when it is frozen, it may be seriously damaged because the bark is more likely to split when the spout, or spile, is installed.
  4. Sample all trees within the same time period.
    Sampling and testing of all trees should occur within a relatively short time period (one hour if possible). This way you control for changes in sap content that may be caused by weather or different times during the sap season.
  5. Sample during the spring sap season.
    Early to mid-season is when sap sugar concentration is likely to be at its maximal level. Sampling during this period offers the best opportunity for detecting differences in sap sugar concentration between trees. Because maple sap may flow in late fall when weather conditions are right, some producers have attempted fall sap collection. However, tapholes drilled in the fall produce only about half as much sap as in the spring. Also, sugar concentrations from fall tapping are about two-thirds below that expected from a spring tapping. Fall tapping for sugar production is therefore not recommended.
  6. Test healthy trees.
    To be selected for the Sugar Maple Tree Improvement Program, a tree must be of good form and free of defects, evidence of harmful insects and disease, and other factors that could influence sap sugar concentration.
  7. Test trees that are capable of flower and seed production.
    Trees selected for the Sugar Maple Tree Improvement Program should be capable of flower and seed production. This way twigs taken from the tree and cloned will produce individuals capable of immediate seed production. Sugar maples acquire flowering and seed production potential at about 30 years of age, which generally coincides with the minimum commercial tapping diameter. Although sap sugar concentration can be measured on small diameter, immature trees, only trees that meet minimum commercial tapping diameter (10 inches diameter at breast height) should be tested as potential candidates for the Sugar Maple Tree Improvement Program.
  8. Tap trees with crowns close to the ground.
    Candidate trees should have well-developed crowns within 30 feet of the ground. This allows the use of pole pruners for cutting twigs from the tree crown. These twigs are used to clone the trees by rooting of cuttings or grafting.
  9. Determine the sap content of the tree using a hydrometer or refractometer.
    Follow the instructions on the hydrometer and refractometer sections of the web page.
  10. If you identify a tree with higher than normal sugar content, test the neighboring trees.
    When a tree is suspected of having sap with above average sugar content, test the sap content of the five nearest trees. Record the results on the Sugar Maple Testing Form. Make sure to mark the tree with higher sap content and the neighboring trees with plastic flagging or in some other way. If possible, measure the selected tree and candidate tree several times during the sap season. The sap sugar content of the candidate tree must be at least 30% sweeter than the average of five surrounding trees (standards) and must exceed the sweetest standard tree by a minimum of 0.5 percent.
  11. If you have a tree you think qualifies for the Sugar Maple Tree Improvement Program, contact your Cooperative Extension agent or the Cornell Uihlein Maple Program.
    Extension agents in many counties are familiar with the Sugar Maple Tree Improvement Program and should be able to help you to determine if you have a candidate tree. If your county Extension agent is unfamiliar with the Sugar Maple Tree Improvement Program, have him or her contact the Cornell Uihlein Maple Program in the Cornell Department of Natural Resources.

Spiles have three important functions. First, spiles allow for the flow of sap into the sap collection system. Second, they support the sap collection system whether it’s a bucket or plastic tubing. Third, they provide a seal against the spread of microorganisms into the tree while sap is being collected.

The plastic spile has replaced the metal spile in large-scale, commercial maple syrup operations. The plastic spile is used because it makes a tighter seal with the plastic tubing that is currently used in most maple operations. Plastic spiles are not intended for use with metal buckets

Measuring Sugar Content in Sap and Syrup



Using a refractometer






Using a hydrometer

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to study the sugar level in plant sap at different plants and different conditions.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

The type of plant and the hours of the day are two independent variable that may affect the amount of sugar in plant sap.

The amount of sugar in plant sap is the dependent variable.

Note: Other conditions such as season, temperature, water and the amount of carbon dioxide in the air may also affect the amount of sugar in plant sap, but we will not study those variables in this project because they require much more time.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

My hypothesis is that plants that grow faster and need more water, will also have more sugar in their sap.

Since the sugar is produced by photosynthesis, immediately after the sunset plant sap will have the highest level of sugar.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”


There are some preparation steps that needs to be completed before your actual experiment. These steps are as follows:

Step 1: Identify the plants that you have access to and can extract their sap. Decide about the method that you want to use to extract the sap and do some preliminary tests to make sure that you can do that with no problem.

Step 2: Identify the method that you want to use to measure the amount of sugar. You may need to purchase necessary tools or build them yourself. Using refractometer is my preferred method because it needs less sap sample.

Step 3: Collect or extract sap samples and store them in plastic or glass containers. The amount of sample depends on the test method that you choose. Seal and label all samples with the date, time, type of plant and it’s location (if you get the sap from a tree). When all your samples are ready you can go to the next step and perform your experiment.


Use the test method that you have selected to measure the amount of sugar in the sap.


  1. Visually inspect your sap sample. If it is not clear, use a filter paper to filter it and get filtered sap.
  2. If the viscosity of the sap that you have collected or extracted is too high, you may want to dilute it with distilled water. If you do this make note of the amount of water and the amount of sap that you mix and calculate the concentration of the sap. For example if you dilute 20 grams sap with 80 grams water, the solution will have 20% sap. After completion of sugar test, you will use this ratio to calculate the amount of sugar in pure sap.
  3. Calibrate your devices with known sugar solutions. Whether you use the hydrometer or refractometer, you will need to do some calibration. Using samples of distilled water, a 10% sugar solution and a 20% sugar solution you calibrate your devices. So for example you will know what is the density of 10% sugar or what is the refraction index of 10% sugar.
  4. Use your devices to do the measurement for each sample and record the results in a table like this:
    SUGAR RATE Morning After noon
    Plant 1
    Plant 2
    Plant 3

If you don’t have a refractometer, you can build one. Following are the instructions.

How to build a refractometer?

In this project you will make a high precession laser beam refractometer that can show the concentration of sugar with accuracy of 1%. This refractometer consists of a laser pointer producing a beam of light that passes trough a prism and hits a screen or wall about 5 to 10 feet away. The prism that you will use is a special hollow prism that you can fill it up with different liquids to measure their refraction rate. Here are the details:

Make a clear glass or Plexiglas container in the form of a triangular prism. You may use silicon glue to connect all the pieces together.

1 mm tick sheet of clear Plexiglas can easily be cut to small pieces. To do that you will first use a sharp object like a utility knife to create grove lines. Then it can easily break from the grove lines with some pressure. Cut 3 pieces of 2″ x 1.5″ to make the walls and one piece of 3″ x 3″ to make the base.



You can then use silicon glue to connect them together. Silicon glue needs about a day to dry and you must be careful with that and read and follow the safety instruction on the glue container. Silicon glue can be used both for glass and plastic. When your container is ready, test it with clean water to make sure that it does not leak. Now is the time to place the laser pointer and the prism in a way that the horizontal beam of laser pointer hit the prism about 1/3rd of inch above the base.


Ready made hollow prisms may also be used for this project. The picture on the right shows a glass hollow prism available at:

  • MiniScience.com,
  • klk.com
  • ScienceKitStore.com
  • ScienceProjectStore.com


Laser pointer can be mounted on a box, but if possible, secure it with more stable tools such as wood, clamps, metal rods, pipes or any thing else that you have access to. In the picture below, the laser pointer is mounted on a laboratory stand.

You will also need to make a fixture for the base of your prism, so it does not move around. To do that you can tape or glue a few extra pieces of Plexiglas to the table or box, around the base of the prism. In this way if you need to remove the prism, wash it and put it back, it will sit at exact place that it was before.

When your setup is ready, add some water to the prism so the laser light goes trough the water. Make necessary adjustments so the light will hit the screen. Mark the screen with a dot where the light spot is and write 0% sugar above that. Remove the water and replace it with a 10% sugar solution. (90 grams water + 10 grams sugar can make it.). With sugar solution, the dot will appear in a different spot. Mark this new spot as well and write 10% sugar next to that. Repeat the above procedure with 20% and 30% sugar as well. Now you should have 4 dots on your screen. You can divide the distance between each two dots by 10 identical spaces and mark them with vertical lines. In this way each line shows 1% difference on sugar concentration.

In one experiment I managed to adjust the distance between the prism and screen in a way that each 10% variation in sugar concentration displaced the light exactly 10 centimeter. In this way every 1 cm was an indication of 1% sugar

Now you are ready to test unknown solutions for their sugar contents.

How to build a hydrometer?

Hydrometers usually are made of glass tubes, however in many cases a home made plastic hydrometer will work as well. As shown in this picture we have inserted a small screw in one end of a straw and applied some glue to secure it. When we insert this hydrometer in fresh water, it floats and only one inch of it will stay out of water. If we place it in a 20% sugar solution, about 2 inches of that stays out of water.

We can graduate this hydrometer using solutions with known density or known concentration of sugar. We will then be able to use it to test the density of unknown solutions.

Materials and Equipment:

List of material depends on your test method.

An inexpensive laser pointer costs about $2.00. It is sold along with many other general merchandizes.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


For each sample you will need to use the density or refraction rate to calculate the rate of sugar in sap.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


List of References