You are correct that no dairy or eggs should be used in any home canning. If this were a thickened sauce, a commerically available product like Clear Jel could be used instead. It may be that the curd had bubbles, even if they were very small. Once under pressure and heat, the product would literally boil and expand, and push its contents out of the jars which are usually under less pressure until the canner reaches its internal pressure. Curds like mayonaise are made by injecting nitrogen into the product while its being canned, also, food preservatives are used, so that can explain why plastic jars are now used for most mayo jars. BTW, mayo jars are now being sold with just 30 ounces instead of the usual full quart amount. The book you got the recipe from may have been a very old recipe, which, under todays standards is not safe to home can.

There is an approved recipe but it uses bottled lemon juice so i'm not sure it would taste great. Here's the link for you.

Here is a link that might be useful: http://www.uga.edu/nchfp/publications/nchfp/factsheets/lemoncurd.html

If you are canning lemon curd, use the recipe provided by Melly. You use bottled lemon juice because it must meet a requirement of acidity in order to be sold, unlike fresh lemons.
If you read the warning on the recipe, it MUST be used within a few months. We still recommend you freeze lemon curd. If it turns brown and you are told to discard it after a short period of time, personally, I would just freeze it. That tells me that there may be a problem with it.

Oh, I thought she posted the recipe here :
Canned Lemon Curd
21/2 cups superfine sugar*
1/2 cup lemon zest (freshly zested), optional
1 cup bottled lemon juice**
3/4 cup unsalted butter, chilled, cut into approximately " pieces
7 large egg yolks
4 large whole eggs
Special Equipment Needed: lemon zester, balloon whisk, 1½ quart double boiler*** (the top double boiler pan should be at least 1½-quart volume), strainer, kitchen thermometer measuring at least up to 180°F, glass or stainless steel medium mixing bowl, silicone spatula or cooking spoon, and equipment for boiling water canning.
Yield: About 3 to 4 half-pint jars

Procedure:

1. Wash 4 half-pint canning jars with warm, soapy water. Rinse well; keep hot until ready to fill. Prepare canning lids according to manufacturer's directions.

2. Fill boiling water canner with enough water to cover the filled jars by 1 to 2 inches. Use a thermometer to preheat the water to 180°F by the time filled jars are ready to be added.

Caution: Do not heat the water in the canner to more than 180°F before jars are added. If the water in the canner is too hot when jars are added, the process time will not be long enough. The time it takes for the canner to reach boiling after the jars are added is expected to be 25 to 30 minutes for this product. Process time starts after the water in the canner comes to a full boil over the tops of the jars.

3. Combine the sugar and lemon zest in a small bowl, stir to mix, and set aside about 30 minutes. Pre-measure the lemon juice and prepare the chilled butter pieces.

4. Heat water in the bottom pan of the double boiler until it boils gently. The water should not boil vigorously or touch the bottom of the top double boiler pan or bowl in which the curd is to be cooked. Steam produced will be sufficient for the cooking process to occur.

5. In the top of the double boiler, on the counter top or table, whisk the egg yolks and whole eggs together until thoroughly mixed. Slowly whisk in the sugar and zest, blending until well mixed and smooth. Blend in the lemon juice and then add the butter pieces to the mixture.

6. Place the top of the double boiler over boiling water in the bottom pan. Stir gently but continuously with a silicone spatula or cooking spoon, to prevent the mixture from sticking to the bottom of the pan. Continue cooking until the mixture reaches a temperature of 170°F. Use a food thermometer to monitor the temperature.

7. Remove the double boiler pan from the stove and place on a protected surface, such as a dish cloth or towel on the counter top. Continue to stir gently until the curd thickens (about 5 minutes). Strain curd through a mesh strainer into a glass or stainless steel bowl; discard collected zest.

8. Fill hot strained curd into the clean, hot half-pint jars, leaving 1/2-inch headspace. Remove air bubbles and adjust headspace if needed. Wipe rims of jars with a dampened, clean paper towel; apply two-piece metal canning lids.

9. Process in the prepared boiling water canner according to the recommendations in Table 1. Let cool, undisturbed, for 12 to 24 hours and check for seals.
   Process only in half pint jars for 15 min. in a boiling water bath.
   Shelf Life: For best quality, store in a cool, dark place (away from light). Plan to use canned lemon curd within 3 to 4 months. Browning and/or separation may occur with longer storage; discard any time these changes are observed.

Prepared lemon curd can also be frozen instead of canned for up to 1 year without quality changes when thawed. Package in freezer containers after straining and cooling to room temperature. To thaw, place container in a refrigerator at 40°F or lower for 24 hours before intended use. After thawing, consume within 4 weeks. (See Freezer Lemon Curd, http://www.uga.edu/nchfp/publications/nchfp/factsheets/freezer_lemoncurd.pdf)

Preparation Notes:

* If superfine sugar is not available, run granulated sugar through a grinder or food processor for 1 minute, let settle, and use in place of superfine sugar. Do not use powdered sugar.

** Bottled lemon juice is used to standardize acidity. Fresh lemon juice can vary in acidity and is not recommended.

*** If a double boiler is not available, a substitute can be made with a large bowl or saucepan that can fit partway down into a saucepan of a smaller diameter. If the bottom pan has a larger diameter, the top bowl or pan should have a handle(s) that can rest on the rim of the lower pan.

For more detailed information on boiling water canning, see "Using Boiling Water Canners" at http://www.uga.edu/nchfp/publications/uga/using_bw_canners.html

Variation:

For Lime Curd, use the same recipe but substitute 1 cup bottled lime juice and 1/4 cup fresh lime zest for the lemon juice and zest.

Other citrus or fruit curds are not recommended for canning at this time.

I put all the lemon curd I made the other night in the fridge so I think it will be fine to eat (soon!) and I really appreciate your feedback. I'm frustrated that this relatively recent and well-reviewed book steered me in the wrong direction.

I still have some Meyer lemons so will try the safe recipe you posted. Thank you again -- I really appreciate all the help!

I would not can lemon curd and I would not make the safe recipe either because bottled lemon juice in a curd sounds really unappealing to me. (Just my personal preference.) It's hard to imagine a delicate curd wouldn't suffer from the heat of processing.

I emailed Linda Amendt about her curd recipe. She said it wasn't tested by any outside agency and that she no longer cans her own lemon curd.

Since lemon curd will keep a good 3 weeks refrigerated and 3 months frozen, I just do that.

Carol

Thanks again for all the help. You all are a wonderful font of canning knowledge! I've repacked the curd into sterilized jars and put them in the freezer.

Tonight I used the pressure canner again and this time made spaghetti sauce. I am delighted to report there were NO problems. Whew!

Some recipe book publications are reprints and compilations of older recipes. If the recipe was from a book that features many recipes for all kinds of non canned foods, its a sure bet that its probably never been tested under todays standards. Usually, the only recipe books that are written about home canning are ones that were published within the last 10-15 years, and feature mostly home canning recipes.

I have her book, and when I got it, read the front of the book. She said something about having a person who was a MFP or someone who understood food safety help her with the recipes. I was still just sitting there, thinking, that was not what I was taught.
Still, even with the extension site recipe, I had run that by the former food safety expert here and was told, no, it was not safe to can. That was before it was on that site, but was told by someone from CalDavis that it was in their files and approved for canning. That was when I asked the food safety expert about it, and was told it must be frozen.
Again, I feel that with a warning to eat it that quickly, I would rather not take a chance.(Plan to use canned lemon curd within 3 to 4 months. Browning and/or separation may occur with longer storage; discard any time these changes are observed. )
It sends up a warning flag to me.
Ken, the book is fairly new, I don't have my copy real handy, but I haven't owned the book too long. Maybe a couple years.
I did try to access her site recently, and found it not online.

Maybe her site was down for maintenance, Linda Lou. I did find it tonight. For those interested, she has posted an errata page with corrections to two of her pickle recipes.

The publication date for the book is 2001, so it is quite recent. I do love the book and will continue to use it. Amendt offers some wonderful recipes for jams and syrups, for example. But I am careful about which recipes I use. Most of hers are quite safe, but as with the curd it's important to double-check with other sources.

Linda Amendt's background is as a fair competitor and judge, not a food scientist. I give her credit that when I emailed she responded very promptly, but her answer referred to USDA standards, and the USDA Guide to Home Canning doesn't mention eggs or butter at all (unless I missed something).

According to a commercial preserver, lemon curd does have a low pH and low water activity, but because of the eggs and butter the heat tends to break the curd unless you change the proportion of ingredients, so for me canning is a moot issue. It's quality, if for no other reason.

Carol

I've never used pressure cooking but I do can lemon curd every year, lots of it (20-40 jars). Ten years ago I checked with UC Davis extension and they gave me a ph number that had to be met to safely can curds. I have access to a microbiologist lab so any time I want to can a new recipe (say Mango/passion fruit curd) I send a sample into the lab for testing. So far I have used Eureka lemons, Meyer lemons, Beears limes, passion fruit with lemon or lime, mango/passion fruit and blood orange. I've been doing it for a long time, so far no horrible deaths. This is good. I have used it for up to two years, it starts getting weird around there, but wasn't bad.

Gwen

I know this is an old post, but gwen_d I would love to hear your recipe and canning directions for passion fruit curd.

I've tried without success, always get an awful texture and overflowing jars, no matter how much headspace I leave.

I don't mind telling people to keep it refrigerated, but it would be nice if I could find a way to keep it safe for mailing.

There is an approved recipe for lemon curd now.

I'm happy to have come across this page. I have a tree full of Meyer lemons, and naturally want to preserve the sunshine. Logic told me I should use a pressure canner because of the eggs, but apparently, not so. I have found several recipes using BWB. But most of the lemon curd recipes advise freezing, to keep it fresh for a year. I think I will freeze it in jars, because I don't see the point in using bottles lemon juice, if I have piles of beautiful lemons.