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

Perhaps I should just let this thread die, but I always concerned about how people assess the information they find on the internet. desertmarcy, I am curious as to why you believe that Dr. Metcalf is a "qualified" individual? Because he is a professor of microbiology? I can assure you, that is NOT sufficient qualification. And the reason I can assure you of that is that I am also a professor of microbiology and I certainly do NOT know as much about food safety as many of the contributors to this forum, including Linda Lou and Carol. There are many areas of microbiology, food safety is a very specialized field. I was curious, so I went to the Cal State Sacramento web page and looked up Dr. Metcalf. His page describes his research with solar cooking. Wondering where he received his degree and what his previous research has been, I attempted to view his curriculum vitae - it was an inactive link. I then did a literature search to see if he has published his findings. He has only one peer reviewed publication on solar water purification and that was from 1999 - considered quite a long time ago in scientific research. On his web page, he states that most of the world believes that water must be boiled for 20 minutes to be safe, but that it can be pasteurized by heating to 65C (149°F). There is an important point here and that is the word pasteurization. It is very different than sterilization. Pasteurization only removes some of the microbes that are present, those that are thought to be most likely to cause illness. It certainly will not remove all microbes. His research appears to be mostly directed toward finding ways that people in developing countries can make their food safer. It is probably a powerful tool in those situations, people don't have money or resources to cook and prepare food the way we do here. Being able to pasteurize water is a huge accomplishment in those situations. However, appying those principles in countries that do have the ability to prepare food with more care seems unwise in my opinion. It is a proven fact that water must be boiled for 20 minutes to inactivate bacterial endospores, including those of Clostridium botulinum which causes botulism. The USDA has carried out extensive studies to determine safe methods for home canning of foods. While they may err on the side of excessive safety (I'm not saying they do, only that they may), they have used scientific experiments to support their findings. I understand the concern for diminishing energy resources, but compromising the safety of one's food seems a very high risk to take in order to conserve. This is, of course, only my opinion and, as stated above everyone has to decide what level of risk is acceptable. I did however wish to point out that one must evaluate information from the internet very carefully and know what the qualifications are of the person providing the information. Perhaps you know more about Dr. Metcalf than I could find. Sorry this is so long.

The OP inquired about the Ball Complete Book of Home Preserving Pizza Sauce. In that recipe 1/2 cup of bottled lemon juice is called for. Since the recipe doesn't mention vinegar as an acceptable substitute, it shouldn't be used even if quadrupled (which clearly would be unworkable for other reasons, taste and consistency among them). Since vinegar is mentioned as an acceptable (though not optimal) substitute in various plain canned tomato products, it can be used for those recipes. The problem is that some may conclude that the ratio of vinegar to lemon juice in those tested recipes (4:1) holds true for all other products containing bottled lemon juice, and that's not the case. That's why the NCHFP says not to switch vinegar for lemon juice [barring those recipes where vinegar has been specified]. In an ideal world the USDA/NCHFP would have communicated more clearly the rationale, but they're over-stressed and under-funded and sometimes they aren't as clear as they'd wish to be. The Chunky Basil Pasta Sauce was developed and tested by Ellie Topp using red wine vinegar and red wine (which is also an acid). A scientist with a PhD in experimental foods, she has the skills and resources to develop new approaches to canning. Canning rests on science and verification, not assumptions. It is an evidence-based discipline. It can be very risky to conclude without proof that one can transpose a method or ingredients from one recipe to another. Perhaps red wine vinegar in some unspecified amount could be used in other recipes in lieu of lemon juice, but only lab testing would confirm that fact. There's no sense in arguing a hypothetical. I think this discussion has begun to get ugly, which is not a good thing for Harvest. I hope we can all just let it go. Carol

Grilled Tomato Sauce From Steven Raichlen Like soup, tomato sauce is one of the dishes you're least likely to think of grilling. But there is a powerful reason to try this sauce. Beyond the mere novelty factor, grilling imparts a gutsy smoke flavor to the sauce and heightens the natural sweetness of the vegetables. Don't take just my word for it. For thousands of years, Mexicans have grilled tomatoes, onions and peppers to make rich-tasting salsas. I have adapted the technique to make an exceptionally flavorful tomato sauce. Serve the sauce over grilled polenta, with any simple grilled fish, or with just about any cooked pasta. Makes about 3 1/2 cups. 5 lucious, ripe red tomatoes 2 - 2 1/4 pounds total, cut in half crosswise, and stem ends removed 1 medium size white onion, peeled and cut into quarters 1 rib celery 4 cloves garlic, peeled and skewered on a wooden toothpick or small bamboo skewer 3 Tbs. extra virgin olive oil 1 tsp. oregano 1/2 tsp. hot pepper flakes 1 bay leaf 6 fresh basil leaves coarse salt (Kosher or Sea salt) freshly ground black pepper 1/4 to 3/4 cup chicken stock, vegetable stock or water Cook the tomatoes, onions, celery and garlic in greased and preheated grill (George Foreman grill) until nicely browned. You may need to cook the vegetables in more than one batch. Transfer the grilled vegetables and let cool. Finely chop the onions, celery and garlic by hand or in a food processor. If using a food processor, run machine in spurts. Heat olive oil in large non-reactive sauce pan over medium heat. Add the chopped onion, celery and garlic, oregano, hot pepper flakes and bay leaf and cook until lightly browned, about 5 minutes. Coarsely puree tomatoes and juices with the basil in a food processor. Add the tomato mixture to the sauce pan, with the vegetables. Bring to a simmer over medium heat, then let sauce simmer gently until thick and richly flavored 8-10 minutes. Season with salt and black pepper to taste. The sauce should be thick but pourable. If it is too thick, add a little stock or water. Remove and discard the bay leaf. The sauce can be refrigerated, covered up to 4 days. Or frozen for up to 2 months. Let the sauce come to room temperature then reheat it in a non-reactive sauce pan over medium heat, stirring often.