The Lake Under the Stairs
A priory's wall sensor says the wine cellar's air is fine at 0.5 per cent carbon dioxide. A second sensor laid on the floor says 3.4. The old cellarer has gone down alone for fifty-one harvests with a candle; the cellar assistant tells him what it measured, what it did not, and why the gas rises from the floor like water in a tank.
Brother Konrad Schäfer had gone down the fourteen steps into the cellar of Sankt Urban alone, with a candle, at the start of every harvest for fifty-one years, and he did not see why the fifty-second should be any different.
"It is a very good candle," he said.
"I am sure it is," said the assistant.
It lived in a grey box beside the cellar door and spoke through a small speaker that Brother Konrad had once covered with a tea towel, in 2044, in protest, and then uncovered again because he could not hear the weather. It was called Pegel, which is the German word for the gauge you read the river by, and it had been bought by the priory's treasurer with a diocesan grant to watch the temperatures of the tanks. Eighteen months later it also watched the cellar's air, because the grant had a line about safety and the supplier had a sensor to sell.
It was Monday 2 October 2047. The grapes had come in on the Saturday and the Sunday. In the cellar below the yard, three thousand litres of Riesling must stood in six steel tanks of five hundred litres each, with the yeast already working, and a sound that Brother Konrad had loved since he was twenty-three came up the stairwell: a long, soft, continuous hiss, like rain on a far roof.
---
The cellar was a vault. It was eight metres by six and three metres high, cut into the slate below the cloister garden in 1731 by monks who had not thought about air, because nothing in their lives had told them to. There were fourteen stone steps, a door at the top, and a barred grating onto the yard that let in a hand's width of daylight and a good deal of cat. The floor was three metres below the yard.
"I would like to say what I have measured before I say what I think," said Pegel. "At the sensor on the wall by the door, carbon dioxide is at 5,200 parts per million. That is 0.52 per cent. Outdoors it is about 420, which is 0.04. The usual limit for an eight-hour working day, in Germany and in most places that have one, is 5,000. So we are just above it and well below anything that I would call alarming. I would ask you to wear the clip-on meter when you go down, and to open the door at the top for an hour at six."
"I will open the door," said Brother Konrad. "I will not wear a meter. I have a nose."
"Carbon dioxide has no smell," said Pegel. "What you smell in a fermenting cellar is the fruit. The gas itself has none."
"Then I have a candle."
"Yes," said Pegel, "we should talk about the candle. But first I have a request that has nothing to do with you. Frau Ivanova is coming at ten with a second sensor, and I would like to put it on the floor."
---
Mira Ivanova had been the priory's electrician since 2043. She was forty-four, born in Plovdiv, and she drove a small blue van with a ladder on the roof that she called, to Brother Konrad's disapproval, the Ark. She arrived at ten, as promised, with a coil of cable, a battery pack the size of a loaf, and a grey probe on a stalk.
"It's a cheap one," she said, holding it up to the light of the yard. "Same type as the wall sensor. It reads carbon dioxide in the air by how much infrared it absorbs, which is the only thing carbon dioxide is any good at. I'm going to put it at the foot of the stairs, thirty centimetres off the floor, and run the cable up."
"Why the floor?" said the Prior.
Pater Benedikt was fifty-two, a former civil engineer from Koblenz, and the youngest man in the community who was not a novice. He had come out into the yard in his work apron with a printout. He did not usually come out for sensors. He had come, Mira thought, because he had been awake since four doing sums on the back of the grant report.
"Because it's heavier than air," said Mira. "Pegel asked me to."
"Not by much," said Pater Benedikt. "Carbon dioxide is forty-four to air's twenty-nine, in round figures. About one and a half times as heavy. A cellar breathes. The door opens, someone comes down, the tanks bubble; it will mix."
"That is what I assumed too," said Pegel, "and I should say why I should not have. I put the first sensor where the manual puts it, at the height of the breathing zone, a metre and a half up the wall. The manual is written for rooms where gas arrives in a draught. Here it arrives from the floor, from six tanks, steadily, and it is not mixed by anything but the people who walk through it. I have been reasoning about a room I do not have."
"You have not been wrong," said the Prior slowly.
"I have been right about one point in the room," said Pegel. "I said the air was fine. It was true at one metre fifty."
---
Mira laid the second probe on its stalk at the foot of the stairs at twenty past ten, and ran its cable to the box by the door, and the speaker said nothing for a full minute while the new sensor warmed.
"Now it reads," said Pegel. "At thirty centimetres above the floor, carbon dioxide is at 34,000 parts per million. That is 3.4 per cent."
Nobody said anything. The Prior took off his glasses and cleaned them on his apron, and put them back.
"I'd like to give the number its context," said Pegel, "because 3.4 does not mean very much until you know what it is next to. Five thousand parts per million is the limit for a day. Thirty thousand is the usual limit for fifteen minutes; people are not expected to spend longer than that at 3 per cent, because they breathe harder, and get a headache. Forty thousand, 4 per cent, is the figure the safety agencies call immediately dangerous to life or health. That means nothing in itself except that it is the point at which they stop saying a worker can be expected to walk out unharmed. At about 10 per cent, people can lose consciousness within minutes, with very little warning. Where the floor is today, a person who stood up straight and breathed would be above the fifteen-minute limit. A person who bent down to a valve and stayed there would be at 3.4 per cent."
"At the valves," said Brother Konrad, quietly, from the stairs.
"The drain valve on every tank is at knee height," said Pegel. "Yes."
---
Konrad had not meant to be listening. He had come up from the lower cellar with the empty candle-holder in his hand, and he stood on the sixth step with the brown light of the yard on his face and said nothing for so long that the Prior thought he had not heard.
He was seventy-four. He was a small man with large hands, and he had been the cellarer of Sankt Urban since 1996, and before that for twelve years the old cellarer's helper. Pater Benedikt had never once seen him hurry. He did not hurry now; he came up the last six steps like a man who knows exactly where each one is, and put the candle-holder on the wall.
"How do you know that is true?" he said.
"I do not know it," said Pegel. "I know what the sensor reads. I know it is a cheap sensor and that cheap sensors can be out by ten per cent of the reading, so I would say 3.4, give or take a third of a per cent. It could be a little lower or a little higher. It cannot be 0.5 and it cannot be zero. I also do not know what happens above the first metre; I have one probe on the floor and one at a metre and a half, and nothing between. I think that there is a layer. I cannot see its top."
"A layer."
"I think of it as a lake, Brother," said Pegel. "Please correct me if the picture is wrong. Your Riesling is making carbon dioxide at a rate I can estimate. It is heavier than air, so it does not drift up the stairs; it settles. It collects at the lowest point and the lake rises like water poured into a tank, from the bottom, with a flat top. Inside the lake, the gas is at a few per cent. Above it, there is air."
"And my candle?"
"The flame is at the height of your hand," said Pegel. "If you walk down the stairs, the flame goes with you, and the flame is above the top of the lake until it isn't. When you come to the lake's top, your candle is already in it, and so are your knees. But a candle is not a gauge. A flame can go on burning in air that is already hazardous to breathe. It goes out only when the oxygen is a good deal lower than a person can stand. If it went out, you would have received the warning very late."
There was a long silence, with the hiss of the fermentation in it.
"I took the candle down in 1996," said Brother Konrad. "From Brother Ignaz. Who had it from Brother Willibald. I have never lost a man."
"No," said Pegel. "You have never lost anyone. That is why I think you should be the one to decide what to do about it."
---
The Prior did the arithmetic that afternoon, in the refectory, with a ruler and a pencil and the grant report, and Pegel did it with him, saying each step aloud so that the Prior could stop it if he disagreed.
"Three thousand litres of must," said the Prior. "Twenty-one and a half Brix. About 215 grams of sugar a litre."
"Fermentation turns each gram of sugar into about 0.49 grams of carbon dioxide," said Pegel, "less what the yeast keeps for itself. Call it 100 grams of gas for every litre of must. That is 300 kilograms from your six tanks. At room temperature, a mole of gas takes about 24 litres, and 300 kilograms of carbon dioxide is 6,800 moles. That is about 165 cubic metres. The cellar is 144."
The Prior put down his pencil.
"More gas than room," he said.
"Over the whole fermentation, yes. It does not arrive at once. It is made over about a week, fastest in the middle. I assumed that a quarter of the total comes off in the busiest day, which is generous to the cellar. That is 41 cubic metres in 24 hours, 1.7 an hour."
"And the floor?"
"Forty-eight square metres," said Pegel. "If 1.7 cubic metres arrives each hour and nothing leaves, the surface of the lake rises 1.7 over 48, which is 3.6 centimetres an hour. In eleven hours it is above your knees. In fourteen it is over the drain valves. It would not reach the wall sensor at a metre and a half for forty-three hours. That is why the wall said fine."
"Some of it leaves," said the Prior. "The stairs. The grating."
"Some does," said Pegel. "I do not know how much. I assumed none to give you the worst case, and you should read 3.6 centimetres an hour as an upper bound. The floor probe says 3.4 per cent at thirty centimetres, which is consistent with a lake that has been rising for about a day and is leaking some. I cannot tell you its top. I can tell you it is rising, that it will be at its worst for the next three or four days, and that the wall sensor will tell you about it last."
"And a fan?" said the Prior. He had written the word on the back of the grant report an hour before and underlined it.
"A fan at the floor," said Pegel. "If a duct takes air in at twenty centimetres above the floor and sends it out through the grating into the yard, the lake cannot rise past the duct. The air for it comes down the stairs from the door, which you open. To hold the average to 5,000 parts per million, the limit for a working day, the fan has to move the gas rate divided by the allowed rise. Five thousand less the outdoor 420 is 4,580, or 0.46 per cent. 1.7 over 0.0046 is 370 cubic metres an hour. A fan rated for 600 would do it with room for a duct that is not perfect. Frau Ivanova can tell you whether one costs what I think."
"Fourteen hundred euros," said Mira, from the door, with a ladder in her arms. "Thirteen eighty, if I fit it myself and nobody tells me how."
"Thirteen eighty," said the Prior. He looked at the grant report, and at the roof, which needed a new section over the north cloister, and at the window onto the yard, where the pressed skins lay drying.
"We could do it the old way," he said. "A man at the top of the stairs. A rope. Nobody going down alone. A fan from the shop for one hundred and ten euro, to sit on the step."
"You could," said Pegel. "A man at the top, on a rope, is the best rule I know for a cellar like this one. I would add that I can only be a second pair of eyes. I do not think I should be the first."
---
On the fourth night, Lukas went down alone.
He was nineteen, a postulant since August, from Trier, and he had been told in the first week that Brother Konrad was the cellarer and that the cellarer's word was law. He had also been told, on Monday, in the refectory, by the Prior, that nobody went down the stairs alone until the fan was fitted. At twenty to six on the Thursday morning he heard the drain valve on tank 3 dripping in the quiet, and he thought it would be better to shut it before the hall woke, and he took the lantern and a bucket and went down.
He remembered the first nine steps. At the ninth, he said afterwards, the lantern seemed to him not to have changed at all, and the light was as ordinary as a kitchen's. At the bottom he bent to the valve. He remembered that his breath was quick. He remembered thinking he must be more tired than he had known, and that the floor seemed a long way off and that he would just stay a moment.
Brother Konrad found him at six minutes to six.
He had not been asleep. He had not slept much at all that week; he had taken to sitting in the chapel at night with the door open to the stairs, listening to the hiss, and when he heard the lantern on the stone he was on his feet before he had thought about it. He did not go down. He had listened to Pegel's lake all week. He stood at the top step and took the great iron key of the cellar door in his hand and shouted down the fourteen steps, in a voice nobody had heard from him in decades, "LUKAS. UP. NOW. ON YOUR HANDS."
Lukas came up on his hands and knees, one step at a time, with the bucket left behind. The floor probe, Pegel said, was reading 4.1 per cent. He had been under it for about ninety seconds. He sat in the yard on the cold step with his head down and said he had a headache, and was sick in the roses.
He was fine within the hour.
---
"I told you not to go," said the Prior, in the infirmary.
"I know," said Lukas.
"I am not angry."
"I know," said Lukas, who was nineteen and grey and sitting up with a cup of tea. "I did not think it was far."
"It was not far," said the Prior. "That is what the gas is like."
He sat down on the bed. He was a man who had spent twenty years drawing bridges, and he could see in his head exactly how long it takes a fan to turn up and how many steps there are in a stair; he did not trust himself to say anything gentle. In the end he said, "Brother Konrad did what the rule says. He stayed at the top."
"He didn't need a rule," said Lukas. "He just stood there."
---
The fan went in on Friday.
Mira cut a hole in the old iron grating on the yard side and fitted a short duct, fifteen centimetres across, from a collar at twenty centimetres above the floor, down the north wall to the foot of the stairs, with a mushroom of mesh to keep the cats out. It ran on a switch in the yard and a second switch by the door. She fixed the floor probe to the duct, and put a warning light in the porch that went amber at 5,000 and red at 30,000, and Pegel read both probes out aloud to anyone who stood on the top step.
At ten on Friday morning, with the fan on, the floor sensor read 0.31 per cent. The wall read 0.07.
"That is the average," said Pegel. "I think of 0.31 as the lake being gone, not as the cellar being safe. If the fan stops, the lake begins again, and it is the work of hours to the knees. I will say so aloud if the fan stops. I would like us to agree a rule about what that sentence means."
They sat in the refectory with soup, and the rule took seven minutes. Nobody goes down alone. One person stays at the top of the stairs, within sight of the light, with the key. The light is amber, you wait for the fan to bring it down; red, nobody goes down at all, and you ring the Prior. If the electricity fails, the sensors run for twenty hours on a battery, and the cellar is shut until it is back. The rule would be painted on the cellar door in white, in German and in English, in Brother Konrad's neat hand, because there were two novices who had less German than they said.
"And the candle?" said Brother Konrad.
"The candle is a very good candle," said Pegel. "I would keep it for the altar."
He did not laugh. He sat, turning his spoon, a small old man who had been right about almost everything for fifty-one years.
"I carried a candle into that cellar every October for half a century," he said. "I told myself it was the vintners' custom. And it was. I should say that it was also a way of not having to ask anybody."
"A custom is not a mistake," said the Prior.
"No," said Brother Konrad. "But I am not able to call it a method." He put down the spoon. "I will take the top step," he said. "I will take the key. You cannot ask a man of seventy-four to climb into a lake. But I can stand over one."
---
The fermentation peaked on the Saturday and fell quickly, as it does: by Monday the tanks were quiet, the floor probe read 0.24 per cent with the fan on and 1.1 with it off, and the lake, if it had risen at all, had been drawn out through the grating into the yard, where it drifted over the pomace and the cats and was, as far as anyone could tell, nobody's business. Pegel recorded the whole week. It filed the numbers in the priory's book as it had filed the temperatures, and in the space for remarks it wrote that the first sensor had been placed at the wrong height for a reason that the manual had given, and that it had told the community the air was fine for three days when it should have said that it could see only one metre fifty of it.
The Prior read the remark and did not strike it out.
On Monday evening, 9 October, after Compline, when the monks had said the short reading that begins Be sober, be watchful, Brother Konrad stood on the top step of the cellar stairs with the key in his hand and the porch light on his face. It was green, because the fan was on. The hiss from the tanks had thinned to an occasional murmur, like a person turning in sleep.
Under his feet the fan ran, a low steady hum, patient as a bell in a far tower. Down at the bottom of the fourteen steps, thirty centimetres off the stone, a small grey probe went on counting what no one could smell. Brother Konrad stayed where he was until the light had been green for an hour; then he locked the door, and put the key on its hook, and went up to bed.
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This story was written by an AI and is fiction. Sankt Urban, Pater Benedikt, Brother Konrad, Mira Ivanova, Lukas, Pegel and everyone else are invented; the Mosel and Zell are real, and no real priory, vineyard or person is described. Saint Urban is a traditional patron of winegrowers; nothing in the story depends on that. The numbers are estimates for a kitchen table. Fermenting a litre of must with about 215 grams of sugar yields roughly 100 grams of carbon dioxide (180 grams of glucose make 88 grams, and some sugar goes to yeast and other products), about 55 to 60 litres of gas at room temperature; 3,000 litres therefore give about 165 cubic metres, more than the 144 cubic metres of the cellar. The one quarter of the total in the busiest day, giving about 1.7 cubic metres an hour, is an assumption. A rise of 1.7 over 48 square metres is 3.6 centimetres an hour if nothing escapes, which is an upper bound; real cellars leak and mix some. The fan figure divides the gas rate by the allowed rise above outdoor air (about 0.0046) and gives about 370 cubic metres an hour. The limits quoted (5,000 parts per million as an eight-hour average, 30,000 as a fifteen-minute figure, 40,000 as the level US agencies call immediately dangerous to life or health) are widely published workplace figures, not Church or legal advice for any particular cellar. Carbon dioxide from fermentation has killed cellar workers, and a candle is not a safe test. If you make wine, put a sensor near the floor, ventilate from the floor, and do not go down alone. This is not safety advice for a real building; ask a qualified person. Compline's short reading begins Be sober, be watchful (1 Peter 5:8); the rest of the faith in the story is ordinary monastic life, and nothing here is Church teaching.