Monday, September 30, 2013

Home-Based Kanban Card Logistics System - Oatmeal and Eggs

Come home to an Oatmeal Sign?

 Can Can Can You Do the Kanban?

Perhaps you work in manufacturing, but most likely you don't. Even if you don't, you've probably heard a lot about "lean" manufacturing, or "just in time" production. Kanban, literally signboard or bill board, is a system where materials are "pulled" to a line instead of "pushed". We'll review this as applied to breakfast.

Both my wife and I nearly always eat hardboiled eggs in the morning. I'll eat two eggs at home, she'll take one to work for a mid morning snack. I almost always eat oatmeal, and she occasionally does. The vast majority of the time I cook these the night before since there just isn't time in the morning. Preparing oatmeal takes me about 20 minutes whereas eggs are 10 minutes of heating plus 15 minutes with the heat off (and lid) of cooking. We'll use eggs for the rest of our example since they are easier to measure.

If we had a push based system, the egg and oatmeal maker would forecast demand and then produce to that demand. Based on demand, I eat 2 eggs per day and my wife has one, meaning 3 eggs per day. So every 2 days the egg maker cooks 6 eggs, or every 3 days you cook 9 and so on. The disadvantage of this is if I wakeup late for work, aren't hungry or if for whatever reason my wife doesn't take an egg to work (say there's a special company brunch or some such thing) then I may cook eggs anyways. This can lead to too many cooked eggs sitting in the fridge, leading to too much inventory and a potential for spoilage. If for whatever reason she decides to eat two eggs, then I won't have anticipated this and we risk running out.

Alternatively, in a pull based system, production occurs as needed. As cooked egg inventory drops low, there is a call for more cooked eggs. One way of communicating the demand signal from the consumer to the producer is by passing a Kanban card which indicates more production is needed.

Home-Based Kanban Cards

On the fridge, you can see two white cards, one has "Oatmeal" and the other "Eggs" written on it. If there is a sufficient inventory of cooked eggs and cooked oatmeal then the cards stay on the fridge. When taking eggs or oatmeal out of the fridge, if you consume enough that the inventory level is too low to support tomorrow's typical requirements (in our case, 3 eggs and 1 serving of oatmeal), then you put the card on the kitchen counter (see previous photo). By having the card in a conspicous place in front of main entrance, when I come home it's immediately obvious that I need to produce more cooked eggs or oatmeal. Once I've cooked more eggs or oatmeal, the card is put back on the fridge.

This simple system is ideal when you have something that is consumed by multiple people and produced by one, especially if the producer is not around to witness the consumption and so doesn't know that more production is needed.

You could apply to anything that is prepared in advance, particularly something you produce multiple of in advance and that has variable consumption. While we don't do it, I've often thought lunches could work well this way.

So why not try a home based Kanban card system, and help improve communication at home between producers and consumers!


  1. Oatmeal taking 20 minutes? You should invest in a water boiler (the Asian style ones)...having boiling water on hand at all times will cut down production times of oatmeal, coffee, tea by at least 75%...sometimes up to 90%. We got one a few years ago and never looked back. Re: Kanban - cool I see it in software development too...would be good to use for keeping track of what's needed from grocery run too.

    1. The Oatmeal I buy seems to take about 20 minutes to cook, this is normal for a steel cut, non-instant type of oatmeal. The 20 minutes does not include the time for the water to boil, which is closer to 2-3 minutes. I agree a water boiler would speed things up, but given our kettle gets used on average less than once a day we probably don't need to keep hot water onhand at all times. I make oatmeal every 4-5 days, don't drink tea, and my wife has tea 2-3 times per week.

      Tracking grocery needs with this is a great idea. Perhaps people don't know, but having a grocery list on the side of the fridge that multiple people add to as items are consumed is something of a Kanban card approach. The only issue with this is if you consume an item and record it on the grocery list, you aren't presenting the list to the grocery buyer. The list can sit on the side of the fridge without the buyer knowing purchases need to be made. This notification is what's missing from the traditional list approach.

      Where have you seen this is software development? I'd be curious to hear the mechanics of how notifications are done, etc.