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When is custard done? (for ice cream)

I love making homemade ice cream, but I can't seem to get the custard right! Is the rule of thumb: thick enough to coat back of a spoon or once mixture reaches a particular temperature?

Lately I have made several ice creams that reach 170-175 F but are not quite thick enough to coat the back of a wooden spoon (when I run my finger down the back of the spoon, most of the trail stays, but the liquid rejoins a bit at the rim). Is the custard done or do I need to keep cooking at that point?

Thoughts?

Thanks!

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  1. I'm sure someone else will come along with a more knowledgeable answer...but I'd say it's done (especially if you've heated it to the temperature your recipe suggests). It will also thicken a bit as it cools.

    Of course, I'm also very impatient and I've frozen custards that weren't close to coating the back of a spoon. I don't know if the eggs were cooked thoroughly, but the ice creams came out fine.

    1. I75 F is the maximum temp that you can cook a custard to with out it breaking. Assuming that it done not have any starches added to it. If you have brought it to that temp it is well cooked. as an aside making Ice cream with eggs that have not been cooked enough to kill the bacteria harbored in them can be quite dangerous.
      Whether or not it will hold a line on the back of a spoon depends not only on the temp. but the strength of the custard (yolks:liquid).

      6 Replies
      1. re: chefj

        "Whether or not it will hold a line on the back of a spoon depends not only on the temp. but the strength of the custard (yolks:liquid)."

        In a nutshell.

        1. re: chefj

          "1 in 10,000 eggs may be contaminated with Salmonella inside the egg shell." That's really low. If you go through a dozen eggs a week, on average, it would take you about 17 years to consume that many eggs.

          You're more likely to contaminate your food during prep. Bringing the food above 140°F will likely kill most bacteria, and freezing will slow their growth significantly.

          In Britain, they don't even put their eggs in the fridge. And eggs are hardly cooked at all in pasta carbonara, in which the eggs are only cooked by the heat from the recently cooked pasta.

          1. re: faddyarbuckle

            Regardless of the statistical rarity and including the possibility that you could contaminate them, it is never a good idea to use uncooked eggs in a preparation that will be stored for a period of time.Especially when the idea is to cook them anyway.
            I stated the "maximum Temp you can bring the custard to is 175 with out it curdling.
            Even at low temps some bacteria can still reproduce some a couple rather rapidly.
            In Pasta Carbonnara and Avogomelo and many other things the food is consumed right away, leaving little time for large scale bacterial growth.
            There are many place where food is handled improperly and many places where food can make you sick.

            1. re: chefj

              Fair enough. But not much, if anything, will grow when frozen. Plus, at what temp do you consider the custard cooked? I did say above 140, to kill most bacteria. And personally, I've never had an issue eating pasta carbonara the next day. To each his own.

              1. re: faddyarbuckle

                Agreed.
                I never use a thermometer. I was taught to use the spoon or the bottom of the pan method. But I could see how this could be more difficult for a home cook.
                160 F seems to be the excepted temp with no starch present in the mixture and 212 F with starch.
                I too leave paella out on the counter over night and eat it the next day, but I would never advise someone else to do the same.

                1. re: chefj

                  I've read that 160-165 kills all bacteria, but I've never used a thermometer either. So I figure if the custard is warm enough, and creamy enough, it's good enough. I would never advise someone else feed others day-old carbonara, or paella, but I figure you're pretty safe using a spoon for custard then freezing, assuming you keep your kitchen clean. I guess someone unfamiliar with custard could use a thermometer to be safe, but I prefer to learn the hard way (ie, broken custard, yuck).

        2. My general test is whether the custard holds a line on the back of a wooden spoon. Of course, the texture desired is at least to some degree a matter of preference.

          As others have alluded to, I would try to up your yolks:cream ratio if you're having trouble with this.

          1. Thank you for the good advice. I have lately been making "lighter" ice creams with fewer yolks... sounds like that could be why my mixture is reaching temperature but not getting thick.

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