ARTICLES · VILNIUS · 3 PIECES, WRITTEN OUT IN FULL
Three long answers to the questions that stall a first batch.
These are the three things I end up explaining most often, so they are written out properly rather than trailed: what the hydrometer is telling you, why cleaning is most of the work, and the five ways a first fruit wine goes wrong. Every example is a batch out of my own log, including the two that died in the first fortnight.
The three articles
What the hydrometer is actually telling you
Specific gravity, a reading you can trust, the ABV arithmetic worked through batch №33, and the two matching readings that mean fermentation has stopped.
MENISCUS · TEMPERATURE · 131.25
Clean first, then sanitise
Why the order matters, what a no-rinse sanitiser does and does not do, and the five places an infection is actually living.
TEN MINUTES PER BATCH
Five ways a first fruit wine goes wrong
Starting blind, feeding it nothing, the wrong yeast for the strength, bottling a stall, and opening it a year before it was ready.
SUGAR · NUTRIENTS · YEAST · TIME
The hydrometer is the only thing that knows.
Fermentation is invisible. A bubbling airlock tells you the vessel is not perfectly sealed and very little else. Two readings, taken properly, tell you the rest.
What the number actually is
Specific gravity is a comparison, not a measurement of sugar. Water at the calibration temperature is 1.000. Dissolve sugar into it and the liquid gets denser, so a heavy fruit must reads about 1.090 — batch №33, nine kilos of pineapple in twenty-five litres — and a thin one reads 1.016, which is where the red seedless grapes of №28 started. Ferment that sugar and two things happen at once: the sugar leaves, and ethanol takes its place — and ethanol is lighter than water, about 0.79. The liquid gets thinner. The number falls.
A hydrometer floats in that liquid and sinks to the depth the density allows. That is the whole of the instrument. It cannot tell sugar from alcohol, which is why one reading on its own is nearly useless and two are worth everything. The drop between them is the fermentation.
Taking a reading you can trust
- Sanitise the trial jar, the thief and the hydrometer. A gravity check is one of the most common ways people infect a batch, because it is the one moment the vessel is open and something is going into it.
- Draw a sample into the jar rather than dropping the hydrometer into the fermenter. Fishing it back out costs you more than the sample did.
- Spin the hydrometer as you let go of it. Carbon dioxide clings to the stem and bubbles lift it — a fizzing sample can read high by 0.002 or more.
- Read at eye level, at the bottom of the meniscus. The liquid climbs the stem and forms a ridge; the number you want is where the flat surface crosses, not the ridge. Reading the top is a consistent error of roughly 0.002, which is a quarter of a percent of alcohol you never made.
- Note the temperature. Most hydrometers are calibrated at 20°C. A warmer sample reads low and a colder one reads high, by something like 0.001 for every 6°C out. In a cellar at 14°C that is a point, and a point is the difference between finished and nearly.
- Do not pour the sample back unless you are certain of everything it touched. I drink it instead. It is the only honest preview you get.
The arithmetic
Alcohol by volume is the drop multiplied by a constant:
ABV = (OG − FG) × 131.25. Batch №33, the
most recent thing in the archive, started at
1.090 and read 0.998
ninety-eight days later. The drop is 0.092; multiplied
out, that is 12.1%ABV, which is
what the log says.
The 131.25 is a rule of thumb built around beer-strength worts, and it drifts once you go above about 1.100 — which is the top of my archive exactly, batch №17, and anything heavier than that will read a little optimistic. Below it, the error is smaller than the error in how you read the meniscus, so it is not worth agonising over. The ABV calculator on this site uses the same constant and says so on the page.
What a finish looks like depends entirely on what you started with, and the spread across the log is wider than people expect:
| BATCH | OG → FG | ABV |
|---|---|---|
| WINE №33 · PINEAPPLE | 1.090 → 0.998 | 12.1% |
| MEAD №29 · BANANA | 1.092 → 1.000 | 12.1% |
| WINE №24 · MANGO | 1.050 → 1.000 | 6.6% |
| CIDER №14 · STRAWBERRY | 1.020 → 0.998 | 2.9% |
| WINE №28 · RED GRAPE | 1.016 → 1.010 | 0.8% |
LOGGED HYDROMETER READINGS FROM THE PUBLISHED BATCH ARCHIVE
Two of those pairs are not the last line in the log. №14 read 0.998 on day 27 and 1.000 on day 94, because the second half of the strawberries went in after the first fermentation was over — sugar back into a jar that had already made its alcohol. №29 read 1.000 on day 30 and 1.010 at day 102, and my note for it says only that it did not clear all the way. A gravity that comes back up is always something going in. It is never fermentation running backwards.
Two readings that match
A still airlock is not an ending. Airlocks stop for all sorts of reasons: the room cooled, the seal is imperfect, the ferment stalled. From the outside a stall looks exactly like a finish, and it will keep looking like one until the bottle is on its side under the stairs.
The test is boring and it is the only one that works. Take a reading, wait three days, take another. If the two match, nothing is eating any more. Then ask the second question, which is why they match. A dry wine that has settled at 0.998 has finished. A jar sitting at 1.090 has not finished — it has quit. Batch №4 read 1.064 on the day it was filled and 1.090 fourteen days later: the number went the wrong way, and there is no ABV printed against it because it never made any. A batch that quit can start again in a sealed bottle when the room warms up. That is the fourth mistake below, and it is the one that makes noise.
Sanitation is most of brewing.
You are not really making wine. You are running a race between organisms and rigging it so the one you chose gets there first.
Clean is not sanitised
These are two jobs and they happen in that order. Cleaning removes the soil — the sugar film, the fruit pulp, the dried ring of krausen around the shoulder. Sanitising kills what is left. A sanitiser cannot work through a layer of dried fruit sugar; it sits on top of it, and underneath, in a crumb of last month’s batch, something is perfectly comfortable.
So: wash first, in hot water with an unscented oxygen cleaner — sodium percarbonate, which is the same compound in the brewing shop’s bag and the supermarket’s, at two different prices. Rinse. Then sanitise. And never take an abrasive scourer to plastic. Every scratch you put in a bucket is somewhere a sanitiser cannot reach, and it is permanent.
What a no-rinse sanitiser does
An acid sanitiser — Star San and its relatives, phosphoric acid with a surfactant — is the standard for good reasons. Mix at about 1.5ml/L, wet every surface, wait 30s, pour it out. You do not rinse it off, because rinsing with untreated tap water undoes the job you just did.
It foams enormously and the foam is not a fault. Made up with distilled or soft water it keeps in a sealed spray bottle for weeks; made with hard water it goes cloudy early and loses strength as the pH climbs. Vilnius water is hard, so mine is made with distilled — a two-litre bottle from any supermarket, and it lasts a month of brewing. Iodophor is the alternative, around 12.5ppm with a minute of contact, and it will stain every plastic thing you own the colour of weak tea.
None of this sterilises anything, and it does not need to. Sanitising knocks the population down by several orders of magnitude, which is all your yeast requires: a large, healthy, well-fed pitch arrives first and takes the sugar before anything else can organise itself. That is the entire strategy.
Where infections actually live
Almost never in the fermenter, which is the thing everyone scrubs. They live in the parts that are awkward to look at:
| WHERE | WHAT I DO ABOUT IT |
|---|---|
| SCRATCHED PLASTIC | Retire it. A bucket with a scored inside is a permanent reservoir, and a new bucket costs less than the batch it will ruin. |
| SIPHON TUBING | Replace it every season. You cannot scrub the inside of a hose and you cannot see it. It is the cheapest insurance on this list. |
| AIRLOCK & BUNG | Blow-off dries into the threads and the trap. Take the airlock apart every single time instead of rinsing the outside. |
| BOTTLING TAP | Dismantle it. Sugar sits in the thread and behind the seat, and it is the last thing every bottle passes through. |
| HANDS & BENCH | Spray bottle. Whatever you set a sanitised lid down on has just become part of the equipment. |
Fruit is not sterile either, and there is nothing sensible to be done about that — you cannot pasteurise a plum without cooking the flavour out of it. What you can do is pitch enough healthy yeast to outrun whatever arrived with the fruit. Batch №2 lost that race in my first week. It went into the jar at 1.010, which is barely above water, so there was almost nothing in it for a yeast to take. Sugar went in afterwards. Fourteen days later it read 1.020 and my note, in full, is: extra sugar added, real vinegar, or more precisely just not tasty, super dry, just not nice. I still do not know what got in. I know the yeast never got out in front of it.
Ten minutes, every time
The routine costs ten minutes and never changes. Fill a bucket with sanitiser. Everything that will touch the must goes into it — spoon, funnel, thief, trial jar, hydrometer, airlock, bung, tubing. Work out of that bucket. Keep a spray bottle for your hands, the bench, and the outside of anything you are about to open. Do not put a sanitised thing down on an unsanitised surface, which is the rule people break most often and notice least.
Ten minutes a batch, against three weeks of waiting to find out. It is the least interesting part of this hobby and it is most of it.
Five ways a first fruit wine goes wrong.
All five are mine, and four of them happened on one afternoon. On 6 August 2022 I filled four jars from the same bananas and treated each one differently. Two of the four are still ageing. Two were terminated inside a fortnight.
One. Starting blind
Batch №2 went into its jar at 1.010. That is ten points above water: there was almost nothing in it to ferment. I took the reading and did not think about what it meant, so sugar went in afterwards to fix a thing I could not yet taste. Fourteen days later it read 1.020 and, in my own words at the time, it was real vinegar — super dry, just not nice. There is no ABV for №2, because it never made any alcohol at all.
The disciplined version of the same move is №28, three years later: the sugar went in as a step feed, two extra feeds of 1.5L of 1:1 syrup each, after the ferment was already running and I could measure what each one did. The sugar calculator will tell you what a target strength actually costs. Guessing at the start and correcting later is not a plan, it is a hope.
Two. Feeding it nothing
A fruit wine is mostly water. №33 is nine kilos of pineapple in 25L; №29 is ten kilos of bananas in 27L. Whatever nitrogen the fruit brought with it is diluted along with everything else, and yeast asked to build a colony out of thin sugar water throws fusel alcohols — the hot solvent edge in a bad homemade wine — and hydrogen sulphide, which is the struck-match smell in week two. Then it gives up.
Use a real nutrient — Fermaid-O, or DAP if that is all the shop has — and split the dose. Something at the pitch, something at 24h, something at 48h, and the last of it by the time the gravity has fallen about a third of the way. All of it at once is worse than half of it staggered, because yeast cannot store nitrogen and most of a single large dose is simply wasted.
Three. The wrong yeast for the strength
Beer yeast is bred for beer, and beer finishes somewhere around 5%. Ask it to carry a wine must and it will work hard, get to the edge of what it can tolerate, and stop — and it will stop before the sugar does. From the outside that looks like a finish. On the hydrometer it looks like this:
Batch №4, 6 August 2022: two kilos of bananas in 2.5L, pitched with beer yeast. It read 1.064 on the day it was filled and 1.090 fourteen days later — the number climbed. My note: looks like the beer yeast could not take the alcohol concentration and that was the end of it; right now it is like syrup with a bit of acid, not much, really not much. It ends with a question to myself — maybe it would be worth trying this one without the added sugar. There is no ABV for №4, because it never made any.
The curve is the whole story, and it is the wrong shape. A fermentation falls. This one climbed, because sugar kept going in and nothing was eating it. Nothing about the outside of that jar looked different from the one standing next to it — №3, the same bananas on the same afternoon, which came down from 1.042 to 1.020 and is still ageing. My note for that one: not bad on the whole, yeast with a good profile, slow, but the closest of the four to a serious wine.
Four. Bottling a stall
A falling gravity means live yeast and unfermented sugar, and a sealed bottle is a pressure vessel. The rule from the first article applies here and it is not negotiable: two readings, three days apart, that match. If they match at 0.998 you have finished — that is where №33 ended. If they match at 1.020 you have to ask why. №3 was sitting at 1.020 on day 14 and my note says plainly that it still had to keep fermenting, because there was no strength in it yet. That is a jar you leave alone, not one you bottle.
Fruit wine also clears slowly, and it leaves a great deal behind. Rack it off the lees and give it time in a vessel where you can watch it: №24 and №27 both gave me about half of what went in once the sediment was left in the demijohn, which is worth knowing before you buy bottles. If you intend to back-sweeten, stabilise first — potassium sorbate and a sulphite, together, and then the sugar. Sorbate on its own, with live yeast still in there, is how you get a geranium smell that never leaves.
Five. Drinking it too young
A young fruit wine is thin, hot and faintly yeasty. That is not a failed batch, that is a young one, and it is the single most common reason a first-time brewer decides this is not for them. Additions need the time even more than the wine does. №13.1 got about 50g of American oak and, tasted early, the oak was overpowering everything else — my note is we will see how it ages, not much so far. Its twin №13.2, the same must, got 400g of frozen blueberries instead: better than the oak one, still carrying the bitterness blueberries bring, and sweetened it should be fine in a year or two.
So keep two bottles back from every batch and write the batch number on them. The best argument for logging everything is opening one of those a year later and knowing exactly what you did to it.
Stop doing this arithmetic in your head.
The calculators use the same constants as the articles above, and the yeast guide answers the question those articles keep raising: which strain will actually survive your room, at your temperature, at the strength you are aiming for. Most of my own log cannot answer it, because I did not write the packet down.
ABV · SUGAR TO TARGET · POTENTIAL · 24 LOGGED BATCHES BEHIND THESE NUMBERS