Green Tea & Possible Gluten Contamination

Green Tea & Possible Gluten Contamination

Many of you may have heard about an FDA study published in June entitled, “Survey of Tea for the Presence of Gluten.” Scientists at the Food and Drug Administration conducted this study. What follows is a brief summary of the situation.

Background: A health care professional recently sent out a mass email with a link to the aforementioned study abstract on PubMed. The email suggested (in my opinion) that gluten contamination found in the study was coming from the tea bags themselves. Colleagues who received this email reached out to me for comment.

I read the entire study (point of note—absolutely no one who knows better should comment on a study based on reading the abstract alone unless they explicitly state that this is all they have done) and then contacted the lead author, Eric Garber. Just to be clear, tea leaves were assessed for gluten NOT the teabags or steeped tea.

What was assessed in the study: Twenty packages of tea (including bags and loose tea) namely 14 green teas, 3 white teas, 2 green and white teas (mix), and 1 peppermint tea were tested for the presence of undeclared wheat using 4 different ELISA assays:

  1. Ridascreen gliadin ELISA (R5)—the assay protocol for foods containing polyphenols and tannins (green tea contains polyphenols) was followed. This means that nonfat dry milk was added to the extraction protocol.
  1. Morinaga gluten (wheat protein) ELISA—there is no special protocol for assessing foods containing polyphenols and tannins.
  1. AgraQuant ELISA Gluten G12—the assay protocol for foods containing polyphenols and tannins was followed. This means that fish gelatin was added to the extraction protocol.
  1. Aller-Tek Skerritt—no special protocol was followed.

Note: FDA has stated that they will use the R5 ELISA and the Morinaga ELISA as part of gluten-free rule enforcement. For Agency regulatory purposes, the FDA stipulates the concurrence between results of two independent assays to improve reliability of results. Manufacturers labeling food gluten-free are not required to test for gluten or use specific tests.

Results of the study:

Morinaga: ALL 20 teas tested below the limit of detection (LOD) for gluten

R5: 12 teas tested below the LOD; the rest tested from 4 to 96 ppm (with 5 testing at/above 20 ppm)

G12: 12 teas tested below the LOD (the same 12 teas that tested below the LOD using the R5); the rest tested from 3 to 95 ppm (with 5 testing at/above 20 ppm)

Skerritt: 11 teas tested below the LOD (peppermint tea tested at 7 ppm using the Skerritt and below LOD using the R5 and G12); the rest of the teas tested from 7 to 175 ppm (with 7 testing at/above 20 ppm)

Further Testing conducted as part of this study (and this gets confusing): The 8 teas testing positive for gluten using the R5 were tested again using the Morinaga and R5 ELISAs and the extraction protocols for each assay. In other words, the R5 was extracted using both the R5 and the Morinaga extraction protocols and the Morinaga was extracted using both the R5 and Morinaga protocols. Samples extracted using the Morinaga extraction solution and tested with the Morinaga and R5 yielded no measurable responses for gluten. Samples extracted using the R5 extraction solution plus skim milk powder and tested with the Morinaga and R5 ELISAs yielded positive responses for gluten.

Western Blot Testing conducted as part of this study: Six tea samples were also analyzed via Western Blot. Blots using the R5 extraction protocol had results proportional to the R5 and Morinaga that also were extracted using the R5 protocol. Blots using the Morinaga extraction protocol were also visible but as mentioned, the R5 and Morinaga that were extracted with the Morinaga extraction solution were negative for gluten.

Question: Why is the Morinaga extraction solution not detecting gluten? FDA states, “the question remains whether wheat, rye, or barley were present in the tea samples or whether the positive responses observed with the ELISAs and immunoblots were actually cross-reactive proteins.” In other words, the FDA is raising the possibility that the results of testing using the R5, G12, Skerritt, and Western Blot are false positives and the results using the Morinaga are accurate.

My concerns:

  1. The R5 has a special extraction protocol for foods that contain polyphenols and tannins; the Morinaga does not.
  2. According to a statement from Tetley tea that was provided to a blogger a few years ago, there was a known widespread contamination of green tea from China. FDA purchased the tea tested in the study in 2013. Please see and
  3. The Chicago Rabbinical Council tested 15 samples of green tea and found small traces of gluten. Please see
  4. FDA does not appear to have run a spike recovery when testing tea for gluten using the Morinaga assay (in a spike recovery a known amount of gluten is added to the product–this helps determine whether the assay is able to assess the gluten content of the particular food matrix).
  5. This study leaves open the question of whether the green tea tested in this study is contaminated with gluten or if something in the green tea is causing false positive results.

What we are doing at GFWD: To help determine the gluten-free status of green tea available today, we have purchased nine different brands, including eight of the brands tested by FDA (FDA’s testing involved eleven different brands). Beginning next week, the tea will be tested using the R5 ELISA and cocktail extraction plus skim milk powder (as recommended by R-biopharm). If there are any positive findings we also may test brewed tea. We also may confirm test results via LC/MS. In the meantime, please do not panic. Even if there is gluten contamination in the tea leaves the amount of gluten in brewed tea will be far less than what may be found in the leaves.


Update September 8, 2015: Test Results Summary

We’ve completed our testing on green tea.

What we tested: The contents of seven brands of tea bags containing 100% green tea.

Brands tested: Bigelow, Salada, Lipton, Tazo, Twinings, Tetley, and Mighty Leaf.

Methodology: Dry tea leaves were removed from individual tea bags and tested in duplicate using the R5 ELISA (R7001) assay and the cocktail extraction solution. Because tea contains polyphenols, a milk additive was added to the extraction procedure per the recommendation of the assay manufacturer R-Biopharm.

Results: Four brands tested below the limit of quantification of 5 ppm gluten; two brands tested at or above 20 ppm gluten; one brand tested between 10 and 20 ppm gluten.

The two brands of tea with tea leaves testing at or above 20 ppm gluten were also tested steeped (e.g., tea brewed using teabags). The steeped tea contained less than 5 ppm gluten.

Bottom line: Gluten contamination was found in some varieties of dry tea leaves (removed from the tea bag). The Gluten level was below the lower limit of quantification in brewed tea when the tea bags were steeped.

Note: When tea leaves are tested for gluten, any fragment of wheat or barley grain will be ground along with the tea leaves for testing. When tea is steeped, the tea leaves and grain remain in the bag (the liquid beverage is tested). Gluten is not all that soluble in water.

Detailed test results are available to subscribers to Gluten Free Watchdog



Share this post

Comments (15)

  • Dick L. Reply

    It would be interesting to know how the brewed tea tests come out, if done. After all, I don’t eat tea leaves– I drink brewed tea, so that’s what I’m really interested in as a celiac.

    July 10, 2015 at 8:36 pm
    • Tricia Thompson Reply

      Hi Dick, This is likely how we will proceed for any dry tea testing at or above 20 ppm gluten.

      July 10, 2015 at 8:46 pm
  • jean Reply

    I wonder why black tea was not tested (only green, white, and peppermint)?
    What is really disturbing is the Kosher certification company’s investigation article of gluten tainted tea. It did not come up with the answer but thought if tea is picked by small stakeholders and harvest grain at the same time then transported by the same means contamination of tea will take place. Doubt if the tea companies will limit their suppliers to only tea growers and nothing else.

    July 10, 2015 at 9:19 pm
  • Mary R. Reply

    I also am curious about black tea as well. I drink decaf Twining’s English breakfast and decaf lady grey teas almost everyday. I drink them using tea bags and Keurig k-cups.

    July 21, 2015 at 12:38 pm
    • Tricia Thompson Reply

      Hi Mary, We have tested other teas, including black (look under food not labeled gluten-free as well as beverages). Once we finish testing green tea, black tea can be assessed. But please keep in mind that the high results are from testing the dry tea leaves. Results are very different when testing steeped tea from tea bags.

      July 21, 2015 at 12:46 pm
      • Mary R. Reply

        Tricia – Thanks! I see PG Tips was tested. I wonder what the green tea companies’ responses will be on where the contamination with gluten came from, if they provide that information. I am not sure I would be comfortable handling these tea bags if the contents are not truly gluten free. Once in a while maybe, but not on a regular basis.

        July 21, 2015 at 1:05 pm
  • Bonnie Reply

    Tricia, thank you for your reminder contained in the “Note” paragraph above regarding: “Manufacturers labeling food gluten-free are not required to test for gluten or use specific tests.” Is it correct to say that this same protocol is true for ALL IMPORTED FOODS labeled gluten-free?

    July 23, 2015 at 10:30 pm
    • Tricia Thompson Reply

      Hi Bonnie, All imported foods labeled gluten-free sold in the US must comply with the US gluten-free labeling rule. That said, other countries have different standards and some may have different rules around testing and the accepted method of testing.

      July 24, 2015 at 12:38 am
  • Lee Reply

    Thank you for this report! I’m curious as to how steeped tea changes the test results?

    September 8, 2015 at 1:45 pm
    • Tricia Thompson Reply

      You are welcome, Lee. If the tea leaves are contaminated with a “piece” of wheat or barley the grain will be ground up with the tea leaves for testing. When tea is steeped, the tea and any grain remain in the bag. Gluten is not all that soluble in water.

      September 8, 2015 at 2:06 pm
  • Andrea Grant Reply

    I wonder if matcha tea has been tested? I’ve participated in some Japanese Tea Ceremonies, where the powder red tea leaves are consumed as part of the drink.

    October 28, 2016 at 12:18 pm
  • mary Reply

    Hi, just wondering about updated tea tests. Just had Trader Joe’s herbal peppermint tea at work, hoping it’s OK, and have a pantry full of Bigelow teas….Mary

    October 25, 2018 at 4:29 pm

Leave a Reply

Your email address will not be published. Required fields are marked *