I don't get it even after a couple of reads. It sounds like an apples to oranges comparison forgive the pun.

She is talking about "percent" rather than pH I think but the figures she gives are in the 6.0 and higher range for lemons vs. 4.5 for bottled juice.

How does one determine the acid "percent" of lemon juice in the juice from one lemon? And what is the pH of that percentage?

Dave

Thanks melly, that was very informative. I am glad that she stressed the importance of using regular lemons versus meyer lemons. IMO that's probably the reason behind the USDA guidelines to use bottled lemon juice; a lot of people wouldn't have known the difference, or wouldn't know what kind of lemons they have. When in doubt, use the USDA guidelines. But for those of us in the know, it's a relief to know we can safely proceed with our Eurekas and Lisbons.

Dave,
Like you, I would have found it simpler if the article had been written in terms of PH rather than acid percentages. She mentions that ReaLemon is measuring acid percentage by weight...presumably, that's how she tested the acid percentage of her lemons.

I 'get it' but I was a chemistry major when I first started university. Not too many people will go the trouble of learning to titrate but she explains it well in a link at the top of her article. They are testing at a quantitative level, not a qualitative level, so is given as the percentage of 'acid' in its pure form in relation to the quantity of contents tested. Undiluted, the pH of pure citric acid is a constant. So if you know the percentage of it in a specific volume of fluids, and compare it to the bottled version, if the percentage is at equivalent or more, then the pH is lower and it's more acidic.

I wonder how my neighbor's ponderosa lemons would compare. My understanding is that they are cross of lemon and citron. They are absolutely huge - some were bigger than grapefruit - and quite tart. I'm pretty sure they would be fine. I've been using my frozen juice cubes for jam making.

calliope - I get that 6% citric acid by weight is more acidic than 4.5% or 4.9%, but is acetic acid higher pH than citric acid? Just wondering why we're told to use 5% acidity vinegar but the FDA approves 4.5% acidity lemon juice (and I thought lemon juice was more acidic than vinegar) - only thing I can figure is that citric acid is more acidic than acetic.

All I'm finding in a Google search is that acetic acid pKa (not the same as pH) is 4.75, and citric acid is 3.06?

I'm sure you could do the calculations, high school chemistry is too long ago for me, but pH of lemon juice (bottled) is around 2.something, Linda Z is saying fresh lemon is not much different, I certainly would substitute fresh lemon juice (or lime) for a recipe that called for vinegar, but what *is* the pH of 5% vinegar?

The complexities of chemistry are beyond me, and many I hazard to guess, so it boils down to a she says (I know her credentials) vs. they say or her word vs. NCHFP word, right?

Dave

What she is saying is that fresh lemon juice has more acid than bottled lemon juice (expressed as grams of citric acid per 100 grams of juice). If true, then she is correct that using fresh lemon juice in your recipes would yield an equal or lower pH than an equivalent volume of bottled lemon juice.

I imagine the FDA chose a minimum of 4.5% (as citric acid) because it represents the bottom of the range found in fresh lemon juice. Setting rules based on the minimum allowed acidity is always safer.

Personally, I use pure crystalline citric acid, which is consistent in acidity and has less of an effect on taste.

TomNJ

TomNJ (or Dave, or anybody) - is there any way to convert a recipe from vinegar or lemon juice to citric acid instead? Annie's Salsa tastes great with lime juice subbed for the vinegar (1 for 1), but I'd like to try Ellie Topp's Chunky Tomato Basil sauce with citric acid (could try lemon juice) instead of the red wine vinegar (we like the red wine, but just looking to cut the vinegar taste).

Nancy - FWIW, under NCHFP's tomato acidification instructions 4 Tbsp vinegar = 2 Tbsp lemon juice = 1/2 tsp citric acid. So I'm wondering if I can sub somewhere between 3/4 tsp to 1.5 tsp of citric acid for the 1/3C vinegar in the Chunky Tomato Basil Sauce?

wcthomas - How much citric acid is equal to how much lemon juice?

Nancy

Yes I would follow the NCHFP's substitution guidelines above. 1/3 Cup of vinegar = 5.3 TBS vinegar = 2/3 tsp citric acid.

TomNJ

4 Tbsp vinegar = 2 Tbsp lemon juice = 1/2 tsp citric acid

Exactly. That is the conversion rate for quarts. Half those for pints of course.

Dave

Here is a link that might be useful: Acidification Instructions

One thing to keep in mind if you merely substitute citric acid crystals for large amounts of vinegar or lemon juice is that you'll also be altering the density of the product.

Carol

Sorry - I completely hijacked this thread. FWIW, for 8C of tomatoes and 2/3C wine, do you think subbing 2/3 tsp citric acid for the 1/3C vinegar would change density too much, should I sub 1/6C (or let's say 1/4C to make it easy to measure) lemon juice instead? Or even just 1/3C lemon juice instead of 1/3C vinegar?

I would dissolve the citric acid in 1/3 c. water.

Personally I wouldn't be concerned in the slightest over such a small change in the density, but if you are, dissolve the citric acid in water as pixie lou suggested.

TomNJ