Everything You Need To Know About Grapes & FODMAPs

Lab testing by both Monash University and FODMAP Friendly have shown us that grapes can vary from containing no FODMAPs at all, to having high FODMAP content. Our article, Are Grapes low FODMAP? is a brief explanation about how that is possible, and how you can approach grapes while follow the low FODMAP diet. This article gets into the science in a very granular way, for those who like to know the how and why.

A Primer on FODMAP Lab Testing

Monash University and FODMAP Friendly are the two entities that are lab testing foods for FODMAPs and providing the public with the resulting information. We have several articles that explain how each of their lab testing procedures are conducted, how you should interpret them, and how to use the smartphone apps where the information is presented.

Please read these articles. You will notice that one article is about how and why lab tests can differ. This is an extremely important article. Once you have read these articles the rest of this post will be much easier to understand.

• Monash University Lab Testing Explained
• FODMAP Friendly Lab Testing Explained
• How To Use The Monash University Smart Phone App
• How To Use The FODMAP Friendly Smart Phone App
• When Low Fodmap Lab Test Results Differ
• FODMAP Content in Food Is Variable

A Grape Is Not Just A Grape

There are over 10,000 varieties of grapes divided into wine grapes and “table” grapes. Table grapes are the ones we eat and are our focus. (Wine grapes are sweeter, which encourages the fermentation process). Australian government documents and the Australian Table Grape Association Inc. list more than 40 table grape varieties available. Ninety-nine percent of the commercially grown table grapes in the United States are grown in California, and there are over 80 varieties available to the public; about 20 of those are considered major varieties, readily found in markets. Then, of course, there are grapes grown in other regions, like the Mediterranean, Italy, China, and Chile, and many are exported.

The point is that a grape is not just a grape. As described in the articles we hope you have read, when lab testing occurs, a food, in this case grapes, is collected from a variety of sources and combined for the actual test. But they are all gathered at roughly the same time. The tests are not combining early season grapes with later season grapes; the only varieties available at the time will be the only ones for sale. Then, of course, we have no information on how those grapes were harvested, handled, stored, etc. And it is literally impossible for the grapes you just bought, or will buy next month, to be the same as these grapes.

Sugar & FODMAP Content of Grapes

Unlike many fresh fruits, grapes are harvested fully ripe. After they are picked, they do not become sweeter, so timing is everything. Every grape variety has a sugar (sweetness) level at which it is perfectly ripe. It is vital that grape growers know when that perfect moment is for harvest. Enter the degrees Brix (°Bx) level.

Learn About Brix

Brix is a level of sugar content found in fruits and vegetables. Named after Adolf Brix, it is the measurement of sugar crystals in the water content in fruit measured with a refractometer. It is used within the grape industry (and the food and beverage industry in general).

Brix (°Bx) is simply how many grams of sucrose are present per 100 grams of liquid solution measured on a scale of 1 to 100. Sucrose is a disaccharide composed of one unit of glucose and one of fructose. When it comes to FODMAPs, we are only concerned when fructose is in excess of glucose.

Grape experts explain that if grapes are harvested when ripe, glucose and fructose are typically present in equal amounts. Fructose is not in excess of glucose; therefore, these grapes are low, or even “no”, FODMAP. This is how it was possible to have a no FODMAP lab test result of grapes.

In addition, Brix levels can vary by more than 100% from grape to grape:

• Table grapes typically have an average Brix of around 13 to 22.
• A Brix of 22 means that approximately 22% of that grape is sucrose.
• For Australian varieties alone, the 2023 government requirements for minimum sugar content per variety range from a Brix of 15 to 19.5. 
• A three-year mean assembled by University Display Gardens, West Madison Agricultural Research Station in Wisconsin showed a range of Brix 16 to 22.
• Some black table grapes are as high as Brix 27.

Why Brix Is Important In Regard to FODMAPs

Here’s why it is interesting to learn about Brix. We have seen via lab testing that grapes can be or become come high FODMAP, perhaps due to the variety, or through poor harvesting procedures, cold storage, or otherwise. If the fructose eventually becomes in excess of the glucose, then the result would be a higher FODMAP grape.

And since we have seen that grapes can vary by as much as 100% in their Brix level, this is one aspect of grape growing, harvesting and distribution that helps us understand why the FODMAP level of grapes can be all over the place.

How & Why FODMAPs Vary In Grapes 

Here are details, at-a-glance, that will help you understand why grapes can range hugely in terms of sugar content, and therefore FODMAPs (and this applies to produce in general, as well):

• If grapes are harvested when ripe, glucose and fructose are usually present in equal amounts. If fructose is not in excess of glucose, then a food is low, or even “no”, FODMAP. This is how it was possible to have a no FODMAP lab test result of grapes.
• Different grape varieties have their own optimum Brix level.
• Sugar content in grapes depends on ripeness at harvest.
• Sugar content in grapes, from the same vine (even the same bunch) can vary when tested in the morning, and again later in the day.
• The side of a bunch of grapes that was exposed to more sun can vary in sugar content from the more shaded grapes of the same bunch.
• Microclimate and terroir (soil, air, wind, precipitation, temperature, humidity, etc.) affect sugar content in grapes.
• Even elevation can affect sugar content. A study in Lebanon determined that Black Pearl and Crimson Seedless had a decreasing sugar content when grown at higher altitudes, whereas Superior Seedless and Red Globe had an increasing sugar content with higher altitudes.
• Sugars tested at harvest will differ in the same grapes tested after storage.
• Cold temperatures (and dehydration, when making raisins), for instance, can encourage the development of fructans, even when none were present before.

IMPORTANT: We do not know these factors in relation to any of the grapes lab tested for FODMAPs, which is why the information in the Monash University and FODMAP Friendly apps should just be used as a guide, and not absolutes.

Grapes: Harvest To Purchase

Let’s look at the life of a grape, from when it is ripe, to when it is ready to be consumed by you. A lot happens in-between, and the process can affect FODMAP content. What we describe here is the optimal situation.

Grapes, unlike many other fruits (like bananas, peaches, and kiwis, to name a few) are harvested when fully ripe; they do not continue to ripen after being picked, making the timing of the harvest crucial.

The process of determining grape ripeness is highly scientific, with standards set and monitored by both the U.S. Department of Agriculture and the California Department of Food and Agriculture (in the U.S.). Factors such as sugar content (the Brix for that variety), color, and the size and uniformity of the bunches and individual grapes are all evaluated before harvesting begins. 

Once harvested, fresh grapes are vulnerable to damage from rough handling, warm temperatures, excessive moisture, and decay-causing organisms. As a result, grape bunches are carefully inspected and packed by hand, often directly in the field.

After picking and packing, the grapes are quickly cooled in cold storage facilities, where the temperature is maintained between 30°F and 32°F (-1.1°C to 0°C), and with a target of 90-95 percent relative humidity. From this point until they reach markets around the world, the grapes are kept in a carefully controlled environment to ensure they remain as fresh as when they were first picked.

Grape specialist and harvest engineers spend time working with the farmers who pick and pack table grapes to make sure they are handled appropriately. Ideal conditions are the goal, but we hope you are starting to see how there are many steps along the way which can affect the final outcome of FODMAP content. 

The variety of grape you buy today or next month might be a high or lower sugar grape; might not be the same as those lab tested; and might not have been harvested/handled/stored correctly.

The Takeaway

1. No need to panic about lab test results for grapes being highly variable.
2. If you have always tolerated grapes, there’s no need to change your approach. 
3. If grapes have given you digestive upset, consider taking a break from them for a while and then experiment with different varieties, starting with small amounts.
4. The most important thing to note is the knowledge that all lab testing is accurate. Lab testing has shown us that grapes can contain no FODMAPs, and be high FODMAP; both are true. Tests reflect just what was tested at the time.
5. The grapes that you buy today or next week literally cannot be the same as any of those lab tested.
6. Use the Monash University and FODMAP Friendly smartphone apps as guides, not absolutes.

Resources

1. Biosecurity and Agricultural Management, Agriculture Standards Regulations, Australia. (2013). Minimum standards of maturity for table grapes. https://www.agric.wa.gov.au/sites/gateway/files/Minimum%20standards%20of%20maturity%20for%20table%20grapes%20in%20Western%20Australia%202020-21.pdf
2. Bogdanovi, J., Mojovi, M., Milosavi, N., Mitrovic, A., Vucinic, and Spasojevic, I. (2008, January 23). Role of fructose in the adaptation of plants to cold-induced oxidative stress. European Biophysics Journal. https://link.springer.com/article/10.1007/s00249-008-0260-9
3. Brasil, I. M., & Siddiqui, M. W. (2018). Preharvest modulation of postharvest fruit and vegetable quality. In Postharvest quality of fruits and vegetables: An overview. https://www.sciencedirect.com/science/article/abs/pii/B9780128098073000019?via%3Dihub
4. (n.d.-b). Crop profile for grapes (table) in California. https://ipmdata.ipmcenters.org/documents/cropprofiles/CAgrapes-table.pdf
5. Dami, I. (2014, January 22). Determining grape maturity and fruit sampling. Ohio State University Extension. https://ohioline.osu.edu/factsheet/HYG-1436
6. Department of Environment, Food and Rural Affairs. (2010). Table grapes. https://unece.org/DAM/trade/agr/promotion/2010_CapeTown/TechnicalSessions/Table%20grapes/tableGrapes_PresentationOfTheStandard.pdf
7. Dharmadhikari, M. (2021). Composition of grapes. Iowa State. https://www.extension.iastate.edu/wine/wp-content/uploads/2021/09/compositionofgrapes.pdf
8. Food and Agriculture Organization of the United Nations. (2005). Grape: Post-harvest operations.https://www.fao.org/fileadmin/user_upload/inpho/docs/Post_Harvest_Compendium_-_Grape.pdf
9. FreshPoint. (2022, May 6). Understanding brix: Is a higher number always better? https://www.freshpoint.com/news/understanding-brix-is-a-higher-number-always-better/
10. Government of Western Australia, Agriculture and Food. (2023). Minimum standards of maturity for table grapes in Western Australia. https://www.agric.wa.gov.au/table-grapes/minimum-standards-maturity-table-grapes-western-australia
11. Guntars. (2024, April 13). How to measure brix in grapes and why it matters. AgNote. https://agnote.com/how-to-measure-brix-in-grapes-and-why-it-matters/
12. Hamie, N. (2023). Maturity assessment of different table grape cultivars grown at six different altitudes in Lebanon. PMC. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10536932/
13. Hazel Technologies, Inc. (2023). The state of Western Table grapes: United States and Mexico season forecast. https://www.hazeltechnologies.com/blog/the-state-of-western-table-grapes-united-states-and-mexico-season-forecast
14. International Fruit Genetics. (2023). Table grape catalog. https://www.ifg.world/licensees/images/downloads/IFG%202023%20Grape%20Variety%20Catalog%20v7-0823.pdf
15. Team, M. F. (2022, December 2). Retested foods – why FODMAP content might change. Monash FODMAP. https://monashfodmap.com/blog/retested-foods-why-fodmap-content-might-change/
16. Tyagi, K., & Maoz, I. (2020). Linalool. Postharvest Biology and Technology. In Linalool – an overview. ScienceDirect Topics. https://www.sciencedirect.com/science/article/abs/pii/S0925521419303813
17. United States Department of Agriculture. (2016). The commercial storage of fruits, vegetables, and florist and nursery stocks. https://www.ars.usda.gov/is/np/CommercialStorage/CommercialStorage.pdf
18. United States Department of Agriculture. (2020). Technical procedures manual – agricultural marketing service. https://www.ams.usda.gov/sites/default/files/media/TechnicalProceduresManual.pdf
19. University Display Gardens. (2014). Table grape fact sheet.https://universitydisplaygardens.wordpress.com/wp-content/uploads/2015/03/tabegrape_factsheet2014.pdf
20. UNL Food. (2022, March 2). Fruits that continue to ripen after picking. https://food.unl.edu/article/fruits-continue-ripen-after-picking
21. Urbina, L. (2023, December 19). The quality of table grapes: The secret of what makes each bite so special. Divine Flavor. https://divineflavor.com/2020/06/05/the-quality-of-table-grapes-the-secret-of-what-makes-each-bite-so-special/
22. Valluru, R., & Van den Ende, W. (2008, July 4). Plant fructans in stress environments: Emerging concepts and future prospects. OUP Academic. Journal of Experimental Botany. https://academic.oup.com/jxb/article/59/11/2905/608172
23. Wiberley-Bradford, A. E., Busse, J. S., Jiang, J., & Bethke, P. C. (2014, November 16). Sugar metabolism, chip color, invertase activity, and gene expression during long-term cold storage of potato (solanum tuberosum) tubers from wild-type and vacuolar invertase silencing lines of Katahdin. BMC Research Notes, BioMed Central. https://bmcresnotes.biomedcentral.com/articles/10.1186/1756-0500-7-801