Using a Refractometer & Sap Press

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At Thursday’s Chapter meeting at Flamig Farm, Dan Kittredge gave us a brief lesson on using a sap press and refractometer to measure food quality. It was towards the end of the meeting and was past daylight so a little difficult to see the numbers in the refractometer. I thought a review plus some links were in order. I would also like to encourage you to get your children and grandchildren involved in food quality testing. On Friday I had my 8- and almost 3-year old grandkids over and we had great fun brixing. They had helped me pick a large bowl of sugar snap peas in my garden before lunch and then at lunchtime they tested each pea before eating it. Even the little one was totally into it. Of course he’d just crow whatever the last number was that he had heard his 8 year old sister say, but she could read the number scale well enough to be fairly close to the true readings. I had them take note of the taste as they tried each number so they would think about whether they noticed one being sweeter than another. The 8 year old took my press and refractometer home to give their “Papa” a lesson on testing things from his garden. That’s my girl! 🙂

If you do not already own a refractometer and press you can invest in the Bionutrient Food Association with a membership and receive the pair as your Thank You gift, or you can look for them online. The refractometers will run from very affordable to ridiculously expensive. An inexpensive one will do fine for the average person so go with whatever you are comfortable with. The modified vice grip is very hard to find and I only know of 1 source who makes them. Pike Agri Lab in Maine is the only place I know where you can find that specific vice grip whose head is modified to have a little channel that directs the sap to the tip.

First, be sure to clean sand and dirt off the produce you are going to test. The sand could scratch and damage the glass lens of the refractometer. If you rinse your produce be sure it is dry before you press it so as not to water down the plant sap.

You only need 1-2 drops of plant sap so a fingertip sized chunk of any fruit or veg will do for pressing. If you put something much larger in your press you’ll wind up with projectiles shooting out the sides, which can certainly be entertaining but makes quite a mess too. In the case of greens like kale or lettuce just roll up the leaf into a cylinder and then fold it upon itself to make a fingertip size ball. If you find some items are too small to ball up well you can gather them up in a small square of tuile, the material that ballet tutus are made of, and squeeze that which will keep the plant in and let the sap out.

Squeeze the sap from the produce while holding it above the refractometer being careful not to tap the glass lens.

Close the lens cover and hold it up to the light for a good reading. You can adjust the eyepiece to dial it in more clearly.

Be sure to keep a journal or notebook with the readings you take from all sources, so you can track the progress whether it is from a store or a local farm market or your own garden. Add any detail you care to that could affect the brix reading. Things like the time of year/date, time of day, weather – Has it been a dry spell? Has it been rainy? – can affect the brix reading. I believe 2 hours after the sun has begun shining on the crop is an optimal time to brix test. Brix leaves and stems and roots – especially if the crop is a root veg but not necessary for something like a tomato plant.

Consult a Carey Reams Brix Chart to see if your item is poor, average, good or excellent. You will notice that some items are not listed on the chart so you will definitely want to record your own numbers and also check with friends who are testing as well. You can use a member of the same plant family to compare with if the exact item you tested is not listed. For example I think Romaine is the only lettuce listed so you can use those readings to compare any variety of lettuce. Keep in mind that the variety of the fruit or vegetable can affect the brix, for instance you may get slightly different readings from one variety to another when testing multiple kinds of carrots. I think we need to have a “Brixing Party” for one of our chapter meetings, so we can test a variety of sources all at once and compare notes. Anyone up for that?

Here are links for the Reams Chart and other information on brix testing:

Here is a link to Dan Kittredge giving a lesson on using a refractometer:

Happy Brixing!

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