Hi-I don't have an answer for you but I thought maybe you might want to repost your question on the vegetable forum. That one has more people on it. This one is such a small subgroup that you may not get an answer for a while.

Good luck! Jude

Composted kitchen waste is better than fresh but in time even that will contribute necessary nutrients. Since these are organic (once living) sources of nutrients, they require activity of soil organisms to convert them into plant accessible nutrients, essentially soluble ions. And soluble ions move through the soil and sometimes are lost to the atmosphere with cultivation - they do not stay in place permanently. You have to keep replacing organic matter to maintain optimum nutrient levels.

From your post I assume your desired pH correction is to acidify the soil. Sulfur is the recommended method - is there a reason you do not wish to use this? Vinegar can also be used but care must be taken with quantity and concentration and any existing plants that may be present. It also takes quite a lot of vinegar to make any appreciable change. Pine needles (or other conifer needles), coffee grounds, fish or most other organic material will have no measurable change on soil pH. The exceptions are peat moss and cottonseed meal but again you would need those in quantity. You really need a permanent mineral component to accomplish this change efficiently and even that is not a one-time fix.

You may find it helpful and informative to visit the Soil, Compost and Mulch forum. There are many excellent discussions on composting and building great soils.

The more organic matter in the soil the better. Vinegar may harm the soil beneficial insects and may not be the best. Organic matter such as compost, manure, kitchen scraps (directly buried in the soil) will all be helpful in restoring pH to slightly acidic.
Here is some more information related to improving the soil in the most natural way. Alkaline soil issues are also addressed here as well as how to compost kitchen scraps.

http://www.elpasotwigs.com/garden/chemical_free.html

http://www.elpasotwigs.com/garden/garden.html

Here is a link that might be useful: El Paso Twigs