Chemistry Is Hard, But Making Jam Is Not
an off-topic post about science, illustrated with anecdotes about heritage recipes, and my own simple recipe for mulberry jam
There’s been a bit of a buzz in the news this week about the firing of 84-year-old chemistry professor Maitland Jones Jr., allegedly because his course was too difficult. Now it may surprise some readers to learn that noone pays me to watch Turkish TV, that my day job is in science, and that I have a PhD in Organic Chemistry. However, I’m not going to comment specifically on Prof. Jones’ case, because everyone knows its true - chemistry is hard. Here’s one of my language apps, teaching the truth in Turkish:
In my own experience, I coasted through high school chemistry with ease, but hit the speed-bumps pretty quickly at university level. By early 2nd year the difficulty was ramping up so much that I was starting to wonder if I’d made the right choice, but by 3rd semester that year something just clicked. Instead of having to rely on rote memorisation (which got me through highschool) I was starting to understand some general principles; building some mental hooks and nails on which to arrange new bits of information. This is the secret to passing OrgChem: it may be as complicated as the family tree in Dark (Netflix 2017), but it does all make sense.
Old-school blogger “Luysii” explains the importance of this understanding for student doctors:
Cynics might say that docs don’t synthesize things or crystallize the drugs they use. Knowing what’s going on under the hood is just esthetic filigree. Just tell them what ‘best practice’ is, and let them follow it like robots. Who cares if they know the underlying science. People drive cars without really understanding what a carburator or a manifold does (myself included).
It wasn’t until I got about 400 pages into the magnificent textbook of Organic Chemistry by Clayden, Greeves, Warren and Wothers (only 1100 action packed pages to go !) that the real answer became apparent. The stuff is impossible to memorize. Only assimilating principles and applying them to novel situations will get you through — exactly like the practice of medicine.
But I claimed this was important for everyone, didn’t I? Not just doctors. Just as I’m not suited for a career in medicine, there are plenty of people who aren’t suited for chemistry. However, everyone can learn the lesson I’m trying to impart today: The world and everything in it is made of atoms and molecules, and it does all make sense. Stick the pieces up on your crazy-wall and join them up with red string; you’ll start to notice the underlying pattern. Their dance is complicated, but watch the electrons moving along the backbone of a molecule, pairing up here, spinning away from each other there, and you’ll learn the rules of the dance soon enough. No matter what you’re doing (in today’s example, its cooking) there are rules that the atoms and molecules involved have to follow, and you can learn their secrets. In the stories, its the secret True Names of all the things that you must learn, to bring them under your Power. In the real word, you measure Numbers.
Alright let me try to explain it with an example. Its Spring here, and I have mulberries. It’s time for mulberry jam, which I’ve never gotten around to making before.
I was looking for recipes online, when I found this advice on how to know when to stop cooking your jam and put it in the jars:
It's a feeling in the thighs. It is how the paddle moves through the fruit. It's the smell. The way the bubbles move and burst that, after a while, tells you when your jam is ready.
This style of cooking may give you that warm feeling of being connected with your food, but frankly, something very important is missing here. A clue is given in the wordplay of the article title, which is “Preserving Knowledge”, but it’s stated plainly in the introduction (emphasis mine):
[…] To my eternal regret, however, I never paid much attention to the bit between the gathering and the eating. The bit where the jam was actually made.
Now I have children of my own and I want to know that what they eat is free from preservatives and processing. I want to make my own jam. I want to pass that knowledge on to them.
You can’t explain “a feeling in the thighs” to anyone else. You can’t write a smell into a recipe so that someone else will experience it the same way you did, and you can’t pass your knowledge on to your children unless you can write it down, because if you simply show them, they won’t pay attention.
You can, however, measure things. And when you measure something you get a number you can write down. Coincidentally while writing this post1 I read a very appropriate quote from Lord Kelvin:
I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarely, in your thoughts advanced to the stage of science, whatever the matter may be.
Of course there is nothing wrong with cooking-by-the-seat-of-your-pants; I do it myself all the time. If I’m in a hurry I’ll chuck ingredients in in whatever quantity feels good. However, if you do this with something like jam, you have to expect a certain number of failed batches that never set, before you really understand what you’re doing. My point today is that there is another option; other people have figured it out before you, so why do you need to re-invent the wheel? When it comes to your kids, why not skip the part where they waste fruit making multiple jars of liquid “jam” they have to offload somehow, and go straight to the part where they make jam the way you taught them?
Here’s another example. Bread making is one thing often considered more art than science, see for example this quote from Daniel Stevens in his excellent book.
I still have that first bread recipe I attempted – both pages of it. And now, years later, I realize why my first loaf was such a disaster. The basic method is fine, but to make good bread you need to understand the process. Some professional bakers and cookery writers skirt this all too briefly. As I discovered, being told what to do is simply not enough. There is so much to know, and I really believe that the more you know, the better your bread will be. Two pages? Not even the best baker in the world could teach bread in two pages.
My first loaf, cooked as an assignment in high school science, was similarly disastrous, and I didn’t try again for many years. As Daniel says above, the recipes don’t teach understanding. Many use standard phrasing like “let the dough rise until it doubles in size”, which I’ve always hated for its imprecise language. Is that double the diameter, or double the volume? That’s a big difference:2 does it matter? If I chose poorly, does that explain why my loaf was inedible? Or was it because of a hundred other things I had to guess, like what a properly kneaded dough is supposed to look like?
If you are lucky enough to have someone teach you how to bread, then get the ruler out! Measure the dough before and after rising. Then you’ll know “that one time we made bread with Grandma, it rose to 2.5 x the diameter, and it worked fine”.
To be honest, my (still novice) bread-making has improved no end since the advent of Youtube recipes. You can see how sticky the dough should be, and watch how and when to add more flour; watch how long they knead for, and see how the kneaded dough changes; and (particularly for me) appreciate the importance of the way that dough is shaped into loaves, so that you don’t lose all that gluten structure you’ve carefully kneaded into it.
To go back to Turkish TV for a minute, I always get hungry every time I watch someone on screen breaking one of those awesomely soft “bazlama” flatbreads. If you’ve never tried bread-making before, a “no-knead” recipe off Youtube is a pretty good introduction to handling and shaping dough. I’ve made “Ramazan pidesi”3 a couple of times following this Youtube recipe and they work really well, both with strong bread-making flour, or just plain/all-purpose flour (the strong flour does work a little better though, if you happen to have some). For "fast yeast" I use this brand, from supermarkets in Australia. Make sure you put the bowl of water in the bottom of the oven while baking, to keep the crust soft. Give it a try!
My grandmother never taught me to make jam or bread; I don’t think either were her specialty. She did however have a prize-winning Christmas pudding recipe, in the style that’s boiled in a cloth. Those CWA ladies got pretty competitive in these things, and my grandmother knew that you can’t just wing it and expect to win a pudding contest by pure luck, adding ingredients according to a feeling in your thighs. A pudding recipe is something you develop over many years, changing things slightly and seeing what works. You cannot make deliberate slight changes to a recipe unless you are also capable of not changing it at all. In other words, to win a pudding contest you must be able to make the thing exactly the same as you did last time. This requires precise measurement and thorough documentation.
Without access to modern scientific instruments, my grandmother developed her recipe using her own standardised measuring device, “The Pudding Cup”. Analogous to how (until recently) there was only one item in the entire world that weighed by definition exactly one kilogram, there was only one “The Pudding Cup”. This thing (pictured) is the last remaining member of some ancient tea set, battered and chipped, and so stained it looks like a disease risk. But this was how she made her puddings the same way each year; so many Pudding Cups of flour, so many eggs, and so on. Due to its importance, “The Pudding Cup” was never used for any other activity, but stored carefully away for most of the year.
You can see the problems here. Of my grandmother’s four children, only one could inherit “The Pudding Cup”, and with it the pudding recipe.4 Its also absolutely irreplaceable, and at the same time extremely fragile. (Before that chip in the side, how much additional water would it have held?).
The solution, as pictured, is obvious to any chemist. Weigh how much water it will hold. Convert the non-standard unit of Pudding Cups into metric units; grams and hence millilitres. Everyone in the family can own a copy of the recipe. If (God forbid) “The Pudding Cup” is broken, the recipe can still be interpreted.
Of course there are additional problems. How tightly did Nanny pack the flour in before levelling it off with a knife, and can you do it the same way? As all chemists (and many cooks) learn, its best to measure flour by weight instead of volume to account for this. There you go; get her to fill the cup with flour and you can weigh that too. This is incredibly easy to do these days; kitchen scales like this are readily available, cheap, and surprisingly accurate.5 You should also buy one of these really good kitchen thermometers, robust enough that you can stick the thermocouple into the food while it cooks, and measure when its ready without opening the oven door.
With just these two measurements (mass and temperature), you can figure out a surprising amount of detail about whats going on in your food while you’re preparing it. How much salt does Grandma add? She says a teaspoon, but she doesn’t measure it, just pours some in her hand till it looks right. You can weight the salt jar before she starts cooking, and again at the end, and calculate how much she really uses. Grandma’s oven is so old, does it really get to the same temperature that yours does? Measure it! If at all possible, measure the temperature inside the food whenever its being heated. What’s the temperature in the middle of the pudding, when Grandma decides its ready? Weigh a spoonful of cookie dough, then weigh again after cooking. Calculate how much water was boiled off in the oven. Write it all down while you’re watching Grandma, and when you repeat it later, measure yours and see if it behaves the same. (When you try to repeat it, maybe your cookies are too soft, and they never went brown. I bet you they weigh more than they should, too!) Whatever Grandma does in the kitchen, I bet you could think of a way to measure it, get a number, and write it down. I never did this with my grandmother’s pudding recipe, but I really should document my mother’s macadamia biscuits one of these days…
Back to the mulberry jam, now that I’ve set the scene with over 2000 words of background, just like every recipe on the internet these days. From the “Preserving Knowledge” article linked earlier:
The advice of experts is all very well but when I read in The Oxford Companion to Food that the perfectly set jam contains 60-65 per cent sugar, 0.5-1 per cent of pectin and a pH level of 2.8-3.4, I get scared.
There we go, that’s the basic quantities sorted. No need to be scared; the quantities are actually pretty forgiving, which is how people successfully made jam before they understood what pectin was. See, CompoundChem says its 65-69% sugar thats needed, while Wikipedia says >60%. There’s a commonly used rule of thumb that says start with equal weights of sugar and fruit, which is how I did it.
Pectin is part of the natural glue that sticks plant cells to each other. When you heat it up in water it dissolves, much the same as sugar does. Pectin is quite sticky; if there is a lot of water present, it’s quite happy to stick to that. If there is very little water present, the long pectin chains will be forced to stick to each other instead, setting into a 3D network that thickens the jam.
The acidity of the jam (i.e. the low pH) helps the setting process. Pectin has its own carboxylic acids in its chemical structure, and if dissolved in pure water, these acids dissociate, leaving the pectin chains with an electric charge. In this state, they repel each other, and they won’t stick together. Add heaps of acid to the pectin solution though, and the charged carboxylates don’t form. If your fruit is sour enough already you might not need added acid for the jam to set, but its a good idea to add some anyway; acid (in this recipe, its citric acid from lemon juice) is also a pretty good preservative, which stops mould or bacteria6 from growing in the jam.
Now most of the jam recipes on the internet seem to mention the basic quantities above, and many also mention adding acid to help with setting and as a preservative. But few recipes give you a proper understanding of what you’re trying to do when you make jam, so if you can’t get it to set, you won’t know what you did wrong.
Here is the most important bit. The sugar is not just there to make the jam sweet; it also helps the pectin set. This is because the pectin chains themselves are actually built out of modified sugars. We don’t have to remove all the water from the fruit to force the pectin chains to stick to each other, if instead we add so much sugar that the water sticks to that instead. In practice, since every fruit will have different amounts of natural sugar and water, its hard to guess the exact amount of sugar to add to get to the magic gel point. So what you do is, you add an amount of sugar that’s less than what’s required to bind up the all the water, then remove the excess unbound water by boiling it away.
Once you understand this, a lot of things make sense:
Don’t simmer the jam; you’re not trying to cook it, you’re trying to boil off some water. Use your biggest burner and get it to a rolling boil.
Stand there and stir it while its boiling, so it doesn’t stick to the bottom and burn. Use a wooden spoon; a metal one will burn your fingers.
The faster you boil off the water, the less time there is for cooking to happen. Boil it fast, so your jam tastes as much as possible like fresh fruit.
Remember you are boiling your fruit up in acid, which slowly breaks down everything in it. If you destroy too much of the pectin, the jam won’t set. Get the water out quicker by using a big wide pot with lots of surface area for evaporation.
Be careful trying to make “low calorie” jam by reducing the amount of sugar. You need sugar to make it set, and also to act as another preservative (microorganisms need water to live, and if the water is all bound up with sugar, it’s not available for them to use).
Now in order to get properly set jam every time, we need the one thing not mentioned in “Preserving Knowledge”, which is that you don’t need to boil it until you can feel it in your thighs; you can measure when the jam reaches the gel point and get it right first time. In a nod to Lord Kelvin,7 you measure the temperature.
Pure water boils at 100°C.8 If the water is stuck to sugar, it takes extra energy to first boil it away from the sugar before you can boil it away into the air. As a result, once the amount of free (unbound) water gets low, the temperature that the jam boils at will increase. Use a thermometer like the one above that I told you to buy,9 and monitor the jam while you boil and stir it. When the boiling point gets to 105°C,10 its at the gel point, and you can bottle it.
Finally, the damn recipe:
Makes enough mulberry jam for 6 of these 200 mL jars. Most people don’t mind eating the stalks of mulberries when they are fresh off the tree, but stalks in jam are less palatable. Recipes often recommend snipping the stalks off the mulberries, which is labour intensive. Instead here I’ve scooped them off the surface of the jam using a strainer. This gets rid of a lot of the seeds too, so technically you might call this a jelly rather than a jam. The few seeds/stalks that are left are not noticeable in the final product.
Ingredients:
1.5 kg of mulberries (would probably also work with other low-pectin fruits e.g. strawberries). Its ok to use ones that are still a bit sour; these have more pectin in them anyway.
1.5 kg of jam setting sugar (this is a mixture of sugar and pectin, I used this brand with 0.7% pectin)
Juice of 1 small lemon (about 70 mL, but you don’t need to be too precise)
Method:
Put your jars on a tray in the oven with the lids sitting loosely on top. Don’t screw them on tight or they may explode.
Switch on the oven and heat it to 120°C. Don’t put cold jars in a hot oven or they may crack.
Cover the mulberries with water and give them a bit of a stir to let any insects etc. float to the top. Drain the water with a colander and add the mulberries to the biggest pot you own (mine is about 20L).
Add in the other ingredients, and heat the pot over high heat.
Stir constantly as the mixture heats up.
When you can’t feel that gritty feeling under the spoon any more, you’ll know the sugar has dissolved. Stop stirring for now.
Using a stick blender, mulch up the mulberries. Try to target every last one as they float on the top, but I’ve done this twice now and I always miss two or three that hide somehow.
Continue heating and stirring. Once you notice some foamy scum on the surface containing a lot of seeds, start scooping off this foam with a fine strainer. Let the liquid drain back in, and discard the mass of seeds and stems (see picture).
Bring the mixture to a rolling boil, and continue stirring while monitoring the temperature. Keep the tip of the thermocouple away from the bottom of the pot, which will be hotter, and away from the surface, which will be cooled by evaporation. The temperature of the mixture will fluctuate up and down a degree or two as you stir, but once it averages 105°C for 20 seconds or so, you can switch off the heat.
Take the tray of jars out of the oven (ideally they were held at 120°C for 20 minutes) and put it on a nice stable surface, like a wooden chopping board. Leave the lids sitting loosely on top to stop germs settling out of the air.
Working quickly, fill jars one by one using a ladle. I added around 250 mL to each 200 mL jar, which fills them right to the neck (the jam does shrink back a little on cooling). Its important to add the hot jam to hot jars to get a good seal and hopefully keep everything sterile. Adding hot jam to cold jars may crack them.
After filling each jar, hold it still with a clean cloth and wipe off any drips from the screw thread. Screw on the lid, finger-tight plus a little extra. (The metal lids will shrink on cooling; if you screw them on too tightly you may find it difficult to open the jars).
Watch the jars as they start to cool and the metal lids will “pop” into place. This will happen quickly if you filled them nice and full. If any jars are lagging behind and not sealing, tighten the lid a little.
Any jars that never seal properly on cooling will have a shortened shelf-life, and should be refrigerated. The sealed jars can be stored in a cool place.
Hat tip Ethan Siegel, who I’ve quoted on this blog before, and undoubtedly will quote again.
Double the diameter = 8 times the volume, at least for spherical loaves.
"Ramazan” is the Turkish word for the Islamic month of “Ramadan”. The word “pide”, along with the Italian word “pizza”, share an origin in the Greek flatbread called “pita”.
It happened to be my mother, and I think her puddings are actually pretty close to the original.
Just remember, if you get water or anything else inside the thing, it will stop working. Don’t use the plastic dust-covers as weighing boats; keep them clean instead. Don’t add any ingredient to a tared container while it’s sitting on the scales because you are guaranteed to spill some; instead put the container on the bench while you fill it, then back on the scales to weigh.
Probably the worst thing you could possibly have growing in your jam is Clostridium botulinum, which can kill people. Unfortunately, boiling the jam isnt enough to kill this nasty bug, but an acidic pH (<4.6) will stop it.
Lord Kelvin gave his name to the Kelvin temperature scale.
Yeah yeah, I know it depends on air pressure as well, and hence on altitude and the like. Don’t @ me.
No I don’t get affiliate points, but maybe I should…
There is some wiggle room here, but not a lot. This site for example says between 104-105.5°C for jams and marmalades. If you get to 106°C, thats too far: its the first stage of candy making.