Alkaline foods with a pH higher than 8

Lutefisk!

https://en.wikipedia.org/wiki/Lutefisk

Microbiota of lutefisk, a Nordic traditional cod dish with a high pH

Most foods have either a neutral or a slightly acidic pH, whereas only a limited number of products have a pH above 8. The Nordic traditional fish dish lutefisk is an exception, with a pH around 12 during production and a ready for consumption pH above 10. Lutefisk is prepared from dried Atlantic cod (Gadus morhua), soaked in water and thereafter treated in a lye solution.

That lutefisk looks pretty good to me! And it is as alkaline a food as you will find, I think.

What, you can't find lutefisk in the supermarket in your part of the world? Well, you must be in the wrong part of the world to find lutefisk.

Tortillas, made by traditional processes, can have a pH above 8 (see table 1 in link). Though commercially processed ones have their pH reduced by addition of acid to prevent spoilage, so they are normally around pH 5-6.

The range of pH varies quite a bit in the (scientific) literature for traditionally produced, with ranges from about 6-8, so this isn't something that is certain, but as you can get tortillas fairly easily in the USA, I thought it would be a useful addition.

Edited to add - the process that makes the tortilla basic is the use of Nixtamal (pronounced with the x as a sh sound), which involves cooking and soaking corn in an alkaline mixture of metal carbonates, traditionally derived from wood ash, but these days usually using limewater (calcium hydroxide). As a result of the nixtamalization, the hull of the corn can be removed and the interior made into a soft dough, which retains some of the alkaline properties of the nixtamalization process.

Another food that is commonly cured in lye is olives, especially those processed in Spain (and, apparently, California?). Most commercial methods will then follow this with a salt brine and a final neutralisation step with vinegar or similar acids, but I've had "sweet" (non-brined) olives that were clearly basic. I can't find a reference in English but some in Italian mention a pH of 8-9.

Almost all food is slightly acidic, but as Harold McGee points out in 'On Food and Cooking', there are two exceptions found in most kitchens: baking powder and egg-whites.

Baking powder doesn't quite qualify as 'food', but egg whites surely do!

Fresh egg whites have a pH of about 7.6, but it increases with age. (source:the incredible egg