Refractometers

Refractometers have been used for over 150 years and were originally used in the wine industry to measure sugar and dissolved mineral levels in grapes prior to harvesting. The concept was then adopted for use in other crop production systems. Most plant sugar levels increase with age and then decrease after maturity and have higher levels in the afternoon of a sunny day than in the morning.  As a general guide a minimum leaf cell sap Brix of 12 is required (refer to the table below crop specific guidelines.)

How to use a refractometer

Prior to use place 2 drops of distilled water on the glass of the refractometer and make sure the reading is set at zero. Most refractometers have a zero-ing screw on the top. Adjust the eyepiece in or out until the scale is clearly readable.

Take a sample of the crop to be tested and roll it in the palm of your hands until the sample is well crushed  then place into a garlic crusher.

Press the garlic crusher gently until a drop of juice is seen forming at the base of the garlic crusher (it is usually easier if you hold the garlic crusher on an angle so all juice droplets form at the same place on the crusher).

Lift up the transparent cover on the refractometer and place 1-2 drops of juice on the glass surface of the refractometer, then lower the cover and look through the eyepiece with instrument aimed towards the light to get a reading.

The division between the blue and white areas on the scale is the reading to take.

If the line is sharply demarcated, calcium is deficient in the sap.  If the line is fuzzy and indistinct, calcium is more available. 

If it is difficult to obtain a reading, hold the cover against the glass with two fingers and rotate the instrument so the cover is facing the ground. This will sharpen the division between blue and white areas.

Cleaning

Spray glass surface and cover with distilled or clean water or use a damp cloth or tissue paper to wipe the refractometer glass clean.

Guidelines to Brix Readings

FRUITS

POOR

AVERAGE

GOOD

EXCELLENT

Apple

6

10

14

16

Avocado

4

8

16

22

Banana

8

10

12

16

Blueberry

8

10

12

18

Cantaloope

8

12

14

18

Casaba

6

8

14

16

Cherry

8

8

14

16

Coconut

4

12

14

16

Grape

8

12

18

22

Grapefruit

8

10

14

18

Honeydew

8

10

14

16

Kumquat

4

6

10

12

Lemon

4

6

10

14

Lime

4

6

10

12

Mango

4

6

10

16

Orange

6

10

16

20

Papaya

6

12

18

24

Peach

8

10

16

20

Pear

8

10

14

16

Pineapple

12

14

20

22

Raisins

65

75

78

85

Raspberry

6

8

12

14

Strawberry

8

12

16

18

Tomato

4

6

10

14

Watermelon

8

12

16

18

 

VEGETABLE

POOR

AVERAGE

GOOD

EXCELLENT

Asparagus

4

6

8

10

Beet

6

8

12

14

Bell Pepper

4

6

8

12

Broccoli

6

8

10

12

Cabbage

6

10

12

14

Carrot

4

8

14

18

Cauliflower

4

8

8

10

Celery

4

6

10

12

Corn Stalk

4

10

18

22

Corn Young

8

10

18

24

Cow peas

4

8

12

14

Endive

4

6

10

12

Escarole

4

6

10

12

English Peas

8

10

12

14

Field Peas

4

6

10

12

Green beans

4

8

10

12

Hot Pepper

4

6

8

10

Kohlrabi

6

8

10

12

Lettuce

4

6

8

10

Onion

4

8

10

12

Parsley

4

8

8

10

Peanut

4

6

8

10

Potato Irish

8

6

7

10

Potato red

8

6

7

10

Potato Sweet

6

8

12

14

Romaine

4

8

10

12

Rutabaga

4

8

10

12

Squash

8

10

14

16

Sweetcorn

8

10

18

24

Turnip

4

6

8

10

 

GRASSES

POOR

AVERAGE

GOOD

EXCELLENT

Alfalfa

4

8

18

22

Grains

6

10

14

18

Sorgum

8

10

22

30

BRIX TESTING IS INCREDIBLY SIMPLE AND THE RESULT IS INSTANTANEOUS!