I recently went to the 2018 Spring ACS meeting in New Orleans (#ACSNOLA). It’s a big chemistry conference and not only was I going in order to see some cool chemistry, but I was also asked to give a couple of talks: of course, neither of them about chemistry (not directly at least). On the Sunday morning I gave a brief five-minute intro to using Twitter and then helped facilitate a Twitter roundtable with Matt Hartings as part of a workshop covering a range of social-media platforms (including some that I am officially too old to have ever heard of).
On the Monday afternoon I talked in a session organized by the ACS Younger Chemists Committee (with some help from the folks at @cenmag, I think) entitled ‘Tales of Chemistry and Cocktails’. I assume I was invited to speak in this session because the organisers confused someone who posts lots of pictures of different gins on Twitter with someone who actually knows something about gin. Nevertheless, I was delighted and honoured to be asked to speak in this mini-symposium, chaired by Lauren Wolf, alongside two friends (and heroes) of mine – Matt Hartings and Raychelle Burks.
I figured I would post a copy of my slides (full pdf version here), but I realised that the talk doesn’t really make that much sense as a standalone file, so below are the individual slides and some notes for each one. (Apologies for those of you on sub-optimal internet connections; I realise this post may take a while to load).
1. Pretty much every sloe-based pun has been used, this is all I’ve got.
2. It all started with a walk through the countryside one afternoon when my wife and I came across some berries that looked like those in the picture below. I had no idea what they were, but my wife was fairly sure they were sloes… well, I’d heard of sloe gin but had never really given any thought to what it actually was, but now I was intrigued.
3. Sloes are the fruit of the blackthorn bush – you can find these all over the place in the UK. They can often be found at the edges of farm fields; they form dense and thorny hedges and do a good job of keeping livestock in fields and people out of them. Sloes are not something you would ever want to eat; they are highly astringent. But… someone, at some point in the distant past, decided to soak them in gin and discovered that it results in a very tasty beverage. I applaud their curiosity.
4. For something that has very few ingredients, there are strong opinions about how to make sloe gin. My recipe can be found here, but if you are going to give it a go, just use it as a rough guide – change the proportions to get the taste you like. Don’t want it quite so sweet? Use less sugar (you can always add more later). Patience is essential though; soaking the fruit for longer (I typically go for 12 months) gives better results (IMHO). There’s an asterisk by the almond extract because this is an optional ingredient.
5. No, you don’t need to wait until after the first frost to pick the sloes – just pick them when ripe. No, you don’t need to prick the sloes with a silver pin or with a thorn from the bush you picked the sloes from; this is chemistry, not witchcraft (even if the former sometimes feels like the latter when you’re in the middle of doing a PhD in it). Use a knife, or simply put the sloes in the freezer overnight – that’s a good way to split them. Don’t use too much sugar – easy to add more later, harder to get it back out if you’ve added too much. Don’t use a fancy, delicate or complex gin – you’re about to throw a lot of fruit and sugar in to it. And, as I already mentioned, leave the sloes in the gin for at least 6 months; a year is better.
6. There is even some scientific literature about sloes – prepare for SCIENCE! Sloes are about 60% water and, once that is gone, almost 90% of what’s left is a mixture of carbohydrates. The remaining 10% includes a lot of interesting organic chemistry.
7. Sloes contain vitamins – a precursor to vitamin A as well as vitamins C (about 30% of what you typically get in an orange) and E (in its various different forms).
8. And there are minerals too! The levels of the bad ones (such as lead and cadmium) are quite low and, after a bit of Googling, seem to be nothing out of the ordinary for wild fruit.
9. I love the fact that this paper didn’t just analyse the chemical composition, but also looked at the physical properties of sloes. I have absolutely no idea why anyone would ever need to know what the terminal velocity of a sloe is – but should this ever come up in a quiz, you’re good to go!
10. The antioxidant and antimicrobial activity of sloes stems from the phenolic compounds, including phenolic acids and flavonoids. One sub-class of flavonoids – anthocyanins – are responsible for the dark purple-ish colour of the sloe berries.
11. Here are the structures of the phenol compounds identified in one particular study.
12. There are claims that the antioxidant properties of sloes may be useful in the food and pharmaceutical industries. But, while they do have antioxidant properties in test tubes, once in the body they are apparently metabolised rapidly and any significant antioxidant properties are lost.
13. There is a whole paper dedicated to studying how the chemical composition of alcoholic solutions of various fruits change over time, at different temperatures and in the presence or absence of sugar – imagine writing the grant proposal to get this funded! The pictures shown on the slide are my own ‘samples’ of sloe gin. After 1.5 years the red colour persists, but 2 years later, the sloe gin is now more of an amber colour – RIP anthocyanins.
14. A lot of data… – a lot of compounds stick around, but the anthocyanins readily decompose it seems. Lower temperatures and the addition of sugar do seem to slow down the decomposition, however.
15. Basically, there is a lot of chemistry going on. Lots of functional groups in the organic compounds from the sloes, not to mention a huge excess of ethanol and some dissolved oxygen probably comes in to the equation too. Likely some photochemistry happening as well… it’s basically a fruity alcoholic mess and it’s not surprising that the chemical composition changes over time, with one of the products ultimately being a brown-ish (presumably polymeric) precipitate.
16. Bear in mind that in the study shown in the previous two slides, the fruit was soaked in 65%-by-volume ethanol for 21 days before being filtered, at which point the liquid was split into portions and either sugar or water was added before the samples were stored at either 15 °C or 30 °C. Making sloe gin is not quite so clinical. First of all, it’s *gin*, not just ethanol; hence the organic menagerie shown below (and that’s just a small selection of the flavour compounds in gin – and the exact profile depends on which gin you use). Also, you’re soaking the fruit for 6 months to a year, so all kinds of chemical chaos may ensue. Tasty chaos, of course.
17. And are you sure that what you are picking are sloes? When wandering through the English countryside, there are all manner of small purple-ish fruits, ranging from sloes, through to bullace (of which there are different varieties), through to damsons (of which there are also a bunch of different varieties that come in different sizes *and* shapes – some are more oval, some are quite spherical…).
18. When I first picked the berries pictured below, I thought the ones on the left were sloes and the ones on the right were bullace. I’m now fairly sure that they are all just sloes, but they were slightly bigger on one bush than on another – and there are good reasons why sloes might come in different sizes too…
19. Here’s a selection of small purple-ish berries foraged from around our village… there’s no reason why a bullace plant might not have crossed with a sloe plant at some point to make a hybrid that produces fruit slightly larger than a typical sloe, but smaller than a bullace. There are also things called cherry plums too (not actual cherries, but plums) which may well have got in on the act at some point, cross-fertilizing with other small members of the plum family to produce another hybrid. And damsons may well have formed directly from the sloe, perhaps via the bullace and maybe the cherry plum got involved at some point too, but it’s all debatable apparently. There’s more questionable parentage flying around than on your average episode of the Jeremy Kyle show.
20. If you want to make sure you are making damson gin (rather than some other random-purple-ish-plum-sorta-thing gin), buy your own damson tree. If you need help picking damsons, small children come in handy (although those are harder to buy – this is one we grew ourselves). These damsons are the Shropshire Prune variety.
21. And just like with sloes, you can make damson gin (and damson whisky and damson brandy). Damsons are typically sweeter than sloes (some of them are not unpleasant to eat – and you will see damson jam, damson cheese* and other damson products). As a typical recipe for damson gin/whisky/brandy, take roughly 750-850 g of damsons, 150-200 g of sugar and 900-1,000 mL of alcohol. The protocol is pretty much the same as for the sloe gin recipe: wash the damsons, slit them with a knife, put sugar, fruit and alcohol in a 2 litre Kilner jar and then leave for 6 months (that’s enough for larger fruit; no need to leave for a year). Filter, bottle and enjoy – again, it will mature once bottled and will get better with age. [*note: not actually cheese, but good with cheese].
22. We did finally find bullace in the hedgerows of Cambridgeshire – these are white bullace, also know as golden bullace (even though they are neither white nor golden; was ‘green’ too much of a stretch?!). They ripen much later than damsons – in fact damsons have usually all fallen off the trees by the time bullace are ripe in October/November. The proportions for bullace gin (or brandy) are 900 g bullace, 250 g sugar and 1 L alcohol. Leave for 6 months, then filter.
23. One summer we noticed a lot of green plums in the hedgerows around the village (they were larger than damsons and so we figured they were small plums) and we just assumed they weren’t ripe yet… until we tried one. They were very sweet and turned out to be greengages. Before our daughter could devour them all, I rescued some for a little gin bath. Greengage gin: 800 g greengages, 100 g sugar, 1 L gin. Leave for 6 months, then filter.
24. These are cherry plums. You can find these growing in country parks and along hedgerows. They’re fairly sweet and you can make jam with them. Of course, you can also make infused gins too…
25. Cherry plum gin and cherry plum vodka (yes, you can use vodka!). 600 g of cherry plums (red, yellow, purple, whatever), 150 g of sugar and 600 mL of gin or vodka. Leave soaking for 6 months or so before filtering.
26. If you are lucky enough to find wild cherries (and if you aren’t, you can always get some from a supermarket), then you can make your own cherry brandy (or cherry gin). Here’s the general recipe I use: 400 g cherries, 500 mL gin or brandy, 125 g sugar. You can filter these after 3-6 months. Once you’ve got the cherry liqueur, don’t throw the cherries away! Remove the stones from them and then coat in chocolate. If you take them in to work, you will gain many friends…
27. One day we stumbled across a quince tree and because I’ll pretty much soak any fruit in alcohol, we figured we’d give it a go. The best way to prepare the quince is to peel them, cut out the incredibly hard cores, and then grate them up in a food processor. The quince will start to go brown before your eyes (real-time chemistry – oxidation – in action), so have everything else ready to go; put the quince into the gin with the sugar in it, seal the Kilner jar and wait 6 months. Filter and you have something that is delicious (I often think of a quince as a bit of a cross between an apple and a pear). 450 g quince, 200 g sugar, 850 mL gin.
28. After getting a copy of this book (probably as a Christmas present from my lovely wife), the one concoction I was eager to try was blackberry whisky. You can’t really go five yards in the English countryside in the late summer without finding a bramble bush covered with blackberries. Why anyone would spend a small fortune on them in a supermarket is beyond me. The recipe is quite simple – fill any container 2/3 full with blackberries (it helps if they are dry), then pour in sugar so it fills the gaps halfway up the pile of blackberries (this only works if the fruit is dry, otherwise just guess). Then, simply top-up the container with whisky – nothing fancy, just something blended and relatively cheap; the author of the Booze book (link above) has fairly harsh words to say about anyone who would use something expensive for this. Leave this for 6 months and then filter. Here, though, time really is key. The stuff will taste OK initially; might still be quite a harsh whisky edge to it though. Leave this for a year (two is better) and then something magical happens*. You’ll have a deep, smooth port-like liqueur that doesn’t taste of whisky or blackberries. It’s amazing. It might be my favourite of all these potions. [*note: not actually magic, simply chemistry…].
29. Instead of using whisky, you can also use gin or brandy with blackberries too. The whisky version is my favourite, but the other two are pretty good as well!
30. Note what the late, great Terry Pratchett said (or wrote – I’m not sure). Make sure that what you are picking is what you think it is and that it isn’t something deadly instead. If you have any doubts, do NOT eat what you’ve picked and certainly don’t soak it in gin and drink it (or indeed give it to your friends). For example, deadly nightshade gin wouldn’t be a good idea – the clue is kinda in the name.
31. If you’re a bit wary of foraging (especially after that last slide), then you can simply buy fruit from a supermarket or from a fruit farm and the chances are that it won’t kill you. In a similar fashion to the quince gin recipe above, you can also make apple gin – there are lots of different varieties of apples you can try and just vary the amount of sugar to taste (the recipe for the one below is as follows: 800 g grated apple (no idea what type they are – they’re from a tree at my wife’s parents’ house), 200 g sugar, 1 L gin and filter after 6 months). The one below on the right is a French drink called ’44’. You take an orange, make 44 incisions with a sharp knife and insert 44 coffee beans, put this in a jar with 44 sugar cubes and a litre of vodka (not gin!). Leave it for, you might have guessed it, 44 days, and then filter. As such, this one is quite quick and you end up with a sort of coffee-augmented cointreau type drink. This recipe was given to us by friends in France – here’s the original to prove it!
32. You can also make interesting drinks with raspberries (that’s raspberry gin below – 475 g raspberries, 100 g sugar, 1 L of gin and filter after just 2 months). If you can find wild raspberries, then great – we never have, but the local fruit farm sells ‘seconds’, which are a bit mushy, but are great for this.
33. All of this is not difficult; just experiment. Do small batches first just in case what you make ends up being revolting (we haven’t made anything truly awful yet, although we don’t speak about the cherry vodka that went wrong…). You’ll notice some variation year-on-year in terms of foraged fruit – some years the sloes are more widespread than others and damsons seem a bit fickle too. And some damsons make great infused gin and some just end up making OK liqueurs. The basic procedure for all of these recipes follows the sloe gin protocol in this post, it’s just the fruit/sugar/alcohol type and ratios that change!