Week 6: Getting March's surplus to August

Week 6 — the storage balance between a harvest curve and a consumption curve, and why one tested recipe is the only safety guidance this course will give

12 April 2027

Open slides — week 6

The question#

Your garden does not produce evenly. It produces a glut, and then it produces very little. The household eats at a constant rate all year.

How much of the peak must you move into the trough, what does that take in space and energy, and at what point does preserving cost more than it saves?

Note what this week is not. Fermentation creates no calories. It moves them through time, and it loses some in transit.

The method: harvest curve against consumption curve#

From week 2 you have a monthly yield curve. Draw the household’s consumption as a flat line across it. The area where harvest exceeds consumption is your surplus; the area where it falls short is your deficit. Storage capacity is sized on the smaller of those two areas, because preserving more than the trough can absorb is just a slower way of composting it.

Three losses to carry: trimming and preparation waste, fermentation mass loss, and the fraction that fails or is not eaten. This course asks you to state each as an assumption rather than supplying a number, because they depend on what you grow.

Safety: one recipe, its own conditions, and nothing beyond that#

This is the only place in the course where a number could hurt somebody, so it is the one place the course refuses to generalise.

The National Center for Home Food Preservation sauerkraut method, adapted from USDA Agriculture Information Bulletin 539:

• 25 lb of cabbage to ¾ cup of canning salt — about 2.25 % salt by weight
• Ferment at 70–75 °F (21–24 °C), “fully fermented in about 3 to 4 weeks”
• At 60–65 °F it takes 5 to 6 weeks; below 60 °F it may not ferment; above 75 °F it may go soft

Four things that method does not say, all of which are routinely attributed to it:

1. It states no pH figure at all. The pH 4.6 threshold comes from US food law, where it is the boundary below which Clostridium botulinum spores will not germinate in a sealed, shelf-stable product. It is not a general pathogen boundary: E. coli O157:H7, Salmonella and Listeria are unaffected by it.
2. The numbers do not transfer to other vegetables. Salt percentage, the vegetable’s own sugars and its buffering capacity were validated together, for cabbage. A different vegetable is a different system.
3. Do not reduce the salt. The source is explicit: “Do not attempt to make sauerkraut or fermented pickles by cutting back on the salt required.”
4. It is US extension guidance. There is no equivalent Australian home-fermentation standard.

A separate university extension source gives 2–2.5 % salt but a different schedule, 68–72 °F for 7–14 days. Both are tested; mixing them is not. An earlier draft of this course did exactly that, which is why you are reading this paragraph.

You will design preservation capacity. You will not make or eat anything for this course.

Worked example: Adelaide#

Adelaide is the mildest site in the set — annual mean 17.0 °C, no frost days, and a long dry autumn. Its fermentation space needs no heating and no cooling in any month, so its counted energy load for this subsystem is zero, and its bench sits at ambient inside the stated 21–24 °C band for most of the useful season.

Its harvest curve is also the most concentrated: winter rain against summer demand gives Adelaide the lowest water closure of the five sites, which pushes its production into the months when rain and warmth briefly coincide. More surplus arriving at once, and a longer trough to cross.

That combination — a sharp glut and a free bench — is why Adelaide leads this week, having led week 5 as the site where seasonal species switching hurts.

Bokashi and silage: the arrow into week 10#

The same microbiology does a second job. Bokashi pre-treatment and silage both acidify organic material before it reaches the compost bay or the digester, lowering odour and stabilising nitrogen that would otherwise volatilise.

That arrow belongs in your week 10 mass balance. Draw it now.

Five sites#

What this week hands you#

A preservation capacity figure in kilograms and litres, its floor area, and — for Darwin and Alice Springs — a temperature-control load that goes straight into week 12’s energy budget at its upper estimate.

This is the last week before the handover, so it is where the six weeks of unknowns become one document: every module so far has left a list of things nobody has measured about this house, and Assignment 1 turns that list into a programme with instruments, positions, frequencies and a cost.

Back to week 6 overview